Earthing systems, EV charging connection options and open PEN detection devices.

00:38:39
https://www.youtube.com/watch?v=gZVx7GbAwlg

概要

TLDRThe video focuses on the installation and safety measures surrounding electric vehicle charging according to UK’s BS7671 Amendment 1. It emphasizes the need to understand different earthing systems such as TT, TNCS, and TNS, addressing the risks associated with PME (Protective Multiple Earthing) supplies when applied to outdoor charging. The speaker provides a detailed exploration of the complex interactions between different earthing configurations and their influence on safety during EV charging, outlining the regulations and highlighting the best practices necessary to mitigate electrical hazards. Several options for maintaining safe operations in various earthing scenarios are presented, although most involve considerable compromises or impractical solutions.

収穫

  • ⚡️ Understanding BS7671 is essential for EV installations.
  • 🚗 Section 722 focuses specifically on electric vehicle charging.
  • 🔌 Different earthing systems like TT, TN-CS, and TN-S each have unique risks.
  • 🔍 PME supplies can shift to TN-CS, increasing safety concerns.
  • ✋ Existing installations may not meet modern safety standards.
  • ⚠️ Electric vehicle charges need proper earthing for safety.
  • 📉 TT systems can mitigate some issues but are challenging to implement.
  • 💡 Using multiple grounding electrodes can lower risk significantly.
  • 🤖 Voltage monitoring devices provide some level of safety, but aren't foolproof.
  • 🏗️ New builds can incorporate integrated grounding systems for better safety.

タイムライン

  • 00:00:00 - 00:05:00

    JW begins by discussing BS7671, focusing on Amendment 1, which pertains to electric vehicle charging installations. He emphasizes the challenges of installations with PME supplies, particularly TNCS systems.

  • 00:05:00 - 00:10:00

    He outlines the three types of earthing systems in the UK: TT, TNCS, and TNS, explaining that TT is the easiest to deal with as it relies on a ground rod, while TNCS is the most common yet fraught with issues due to interlinked neutral and earth connections.

  • 00:10:00 - 00:15:00

    Additional details about TNS installations are provided, highlighting the separation of conductors and how external damage can potentially reclassify a system as TNCS if repairs introduce linkages between neutral and earth.

  • 00:15:00 - 00:20:00

    JW illustrates how external circuitry might be upgraded or replaced with TNCS components, leading unsuspecting property owners to believe they still have a TNS supply, though they may actually be dealing with the hazards of a TNCS.

  • 00:20:00 - 00:25:00

    Transitioning to TT systems, JW outlines the drawbacks, including difficulties in electrode installation near buried services and maintaining safety distances from other underground infrastructure.

  • 00:25:00 - 00:30:00

    A scenario involving shared charging points between two houses illustrates the perilous voltage disparity that can arise when one side makes a TT conversion, while the other remains with a TNCS connection, posing shock hazards.

  • 00:30:00 - 00:38:39

    In conclusion, JW summarizes that TT installations pose fewer risks if already established, while newer TNCS installations might not be as safe as assumed, emphasizing the importance of adhering to regulations and considering practical safety measures when installing EV chargers.

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ビデオQ&A

  • What is BS7671 Amendment 1 about?

    It covers regulations for electric vehicle charging installations, particularly concerning earthing methods.

  • What are the three types of earthing systems discussed?

    The three types are TT, TN-CS, and TN-S.

  • Why are PME supplies problematic for EV charging?

    Due to potential voltage risks if the PEN conductor is damaged, creating dangerous conditions.

  • Can you convert a TN-CS supply to a TT supply?

    It's complicated due to various underground service factors and potential safety issues.

  • What are the five options to ensure safety when using PME for EV charging?

    The options include using specific devices that monitor voltage and earth resistance, among other methods.

  • Is a TT earthing system preferable?

    A TT system can be safer if properly implemented, but comes with its own set of challenges.

  • How can the dangers of high voltage be mitigated?

    By using additional ground electrodes and ensuring low resistance connections.

  • What is the significance of the 70 volts regulation?

    It aims to prevent dangerous voltage surges in the event of a fault.

  • Are there any devices that ensure safety for outdoor charging points?

    Some devices monitor and disconnect in the case of voltage detection, but are not foolproof.

  • What is the ideal solution for EV charging installations?

    A proper TT system with low resistance electrodes or three-phase monitoring devices.

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オートスクロール:
  • 00:00:04
    hello i'm jw
  • 00:00:05
    today we'll be looking at bs7671 but
  • 00:00:08
    it's not actually in this book here it's
  • 00:00:09
    on that amendment one which came out a
  • 00:00:11
    while ago and then there was those
  • 00:00:12
    corrections that came up with it as well
  • 00:00:13
    and all of that bother now
  • 00:00:15
    section 722 which is what amendment 1
  • 00:00:17
    actually covers is
  • 00:00:18
    referring to electric vehicle charging
  • 00:00:20
    installations only
  • 00:00:22
    and what we're going to look at is how
  • 00:00:24
    you're going to install something
  • 00:00:26
    when you've got a pme supply normally
  • 00:00:29
    called
  • 00:00:30
    a tn cs when you actually get to the
  • 00:00:32
    property itself
  • 00:00:33
    and there's five things you can pick
  • 00:00:35
    from some of which may or may not be
  • 00:00:37
    useful and others
  • 00:00:38
    are basically downright impractical and
  • 00:00:41
    before you thought about just going oh
  • 00:00:42
    it doesn't matter we've got a tns supply
  • 00:00:44
    here
  • 00:00:44
    well think again because most tns
  • 00:00:46
    supplies in the uk
  • 00:00:48
    might not be tns anymore they could
  • 00:00:50
    actually be tmcs
  • 00:00:52
    in disguise so let's just have a look at
  • 00:00:54
    that as well and
  • 00:00:55
    how that actually works out and the
  • 00:00:57
    third option of course is to make it tt
  • 00:01:00
    but just a minute because that might not
  • 00:01:01
    be any good either because there's a
  • 00:01:02
    whole pile of problems involved with
  • 00:01:04
    that
  • 00:01:04
    as well now in the uk there's three
  • 00:01:07
    types of earthing
  • 00:01:08
    system that are available and these are
  • 00:01:11
    pretty much what you're going to be
  • 00:01:12
    given there's not really a whole lot of
  • 00:01:13
    choice in what you're going to get
  • 00:01:15
    so the first one and it's actually the
  • 00:01:17
    easiest one is a
  • 00:01:18
    tt arrangement this is where you don't
  • 00:01:21
    have
  • 00:01:21
    any kind of connection provided by the
  • 00:01:23
    electricity company
  • 00:01:25
    it's just a question of a rod or other
  • 00:01:27
    electrode in the ground
  • 00:01:28
    and that is it all you get from the
  • 00:01:31
    supplier are the two conductors
  • 00:01:33
    line and neutral so if you get a
  • 00:01:36
    property that's already got
  • 00:01:37
    a tt installation then that's basically
  • 00:01:39
    going to be using there's no choice and
  • 00:01:41
    this is actually by far the easiest
  • 00:01:43
    option
  • 00:01:43
    and so if you get one of those then
  • 00:01:45
    character of lucky because
  • 00:01:47
    that's your only option and you don't
  • 00:01:49
    necessarily need any special equipment
  • 00:01:50
    or whatever
  • 00:01:51
    certainly in the question of those five
  • 00:01:53
    items which only apply to
  • 00:01:55
    pme supplies next type of supply which
  • 00:01:58
    is by far the most common is a
  • 00:02:00
    tn cs
  • 00:02:03
    and this is typically found on newer
  • 00:02:05
    properties and newer meaning anything in
  • 00:02:06
    the last
  • 00:02:07
    25 or 30 years or so and also any which
  • 00:02:10
    have had
  • 00:02:10
    new services things put in since then
  • 00:02:14
    and with that one you do get the three
  • 00:02:15
    conductors so you're getting a line
  • 00:02:18
    neutral and the earth connection
  • 00:02:21
    crucially on this one at the actual
  • 00:02:23
    cutout position where it comes into the
  • 00:02:25
    property
  • 00:02:26
    the neutral and earth are linked
  • 00:02:27
    together
  • 00:02:29
    and then outside of the property there's
  • 00:02:31
    actually only two wires which will be
  • 00:02:33
    the l there
  • 00:02:34
    and then the combined neutral and earth
  • 00:02:36
    conductor
  • 00:02:37
    also called a pin conductor protective
  • 00:02:41
    earth and neutral
  • 00:02:42
    and the problems around this one and why
  • 00:02:45
    you can't just go shoving any old stuff
  • 00:02:46
    on the thing particularly outside
  • 00:02:48
    all the rises where this conductor here
  • 00:02:50
    is the one that gets broken
  • 00:02:52
    due to some kind of fault and then what
  • 00:02:54
    you end up with there's no neutral ore
  • 00:02:56
    earth connected at the installation and
  • 00:02:58
    all of this part becomes live because
  • 00:03:00
    then when you have your load connected
  • 00:03:03
    let's put a light or something in there
  • 00:03:06
    it's connected back here but these are
  • 00:03:07
    linked together so if this connection
  • 00:03:09
    goes away
  • 00:03:11
    this is live here so is this and then so
  • 00:03:13
    is all of the stuff within the
  • 00:03:14
    installation
  • 00:03:15
    and this conductor and then is obviously
  • 00:03:16
    what's being broken and damaged but
  • 00:03:18
    as long as that's intact not a problem
  • 00:03:23
    and that's what those five things in the
  • 00:03:24
    legs actually apply with so
  • 00:03:26
    look at those shortly now the third type
  • 00:03:29
    of installation
  • 00:03:30
    is a tns
  • 00:03:34
    very similar to what we had there but
  • 00:03:35
    the difference being
  • 00:03:38
    that you've got your line neutral on
  • 00:03:41
    earth
  • 00:03:42
    inside the property when this goes
  • 00:03:45
    outside the property it's actually still
  • 00:03:48
    three separate conductors like that
  • 00:03:51
    so if one of these gets broken obviously
  • 00:03:54
    thinking's not gonna work
  • 00:03:55
    but there's no link here between the
  • 00:03:56
    neutral and earth conductors so
  • 00:03:58
    problems to get with a t and cs supply
  • 00:04:00
    don't exist because that conductor that
  • 00:04:02
    could be broken
  • 00:04:03
    doesn't exist either and even if both of
  • 00:04:05
    these got busted
  • 00:04:06
    it doesn't matter because again the
  • 00:04:08
    neutron earth are not linked together
  • 00:04:10
    at the installation the only place these
  • 00:04:13
    are linked is way back at the
  • 00:04:14
    transformer
  • 00:04:15
    where the cable off seat comes from now
  • 00:04:18
    that's all very well so you might be
  • 00:04:19
    tempted to think well if you've got a
  • 00:04:20
    tns supply well that's fine
  • 00:04:21
    none of those things in the regulations
  • 00:04:23
    apply so obviously it's tns it's not a
  • 00:04:25
    tncs but
  • 00:04:26
    the problem is that do tns supplies
  • 00:04:29
    really exist anymore
  • 00:04:31
    and the answer is probably no they do
  • 00:04:33
    not
  • 00:04:34
    because even if you've got something at
  • 00:04:35
    your house which it claims to be tns an
  • 00:04:37
    older piece of stuff or whatever
  • 00:04:39
    there's a very good chance elsewhere in
  • 00:04:41
    the network outside your house where you
  • 00:04:42
    can't see
  • 00:04:43
    bits of that network may have been
  • 00:04:45
    upgraded or replaced or repaired
  • 00:04:47
    with pieces of cable or usually used on
  • 00:04:50
    the tncs
  • 00:04:51
    installation so let's just have a look
  • 00:04:53
    at how that could occur
  • 00:04:55
    and why tns may not be
  • 00:04:58
    what you think it is now this is what a
  • 00:05:00
    tns supply would look like
  • 00:05:02
    if you could see under the road outside
  • 00:05:04
    here's your house with the
  • 00:05:06
    three connections inside so line neutral
  • 00:05:08
    and earth there
  • 00:05:10
    and then the cable itself has three
  • 00:05:12
    separate conductors which go all the way
  • 00:05:14
    back to the transformer
  • 00:05:15
    now it could be nearby or it could be uh
  • 00:05:17
    half a mile down the street
  • 00:05:19
    so the point here is you've got three
  • 00:05:20
    entirely separate conductors there
  • 00:05:22
    the only connection between neutral
  • 00:05:26
    and earth here is back at the
  • 00:05:28
    transformer so if this gets damaged or
  • 00:05:29
    broken at any point
  • 00:05:31
    even if it's just one two or all three
  • 00:05:32
    conductors it doesn't actually matter
  • 00:05:34
    because at no point
  • 00:05:36
    are the neutral and earth conductors
  • 00:05:38
    combined or
  • 00:05:39
    linked together in any way and that's
  • 00:05:41
    pretty much how it's been for a very
  • 00:05:42
    long time
  • 00:05:43
    so uh that's absolutely fine there but
  • 00:05:46
    of course the problem occurs when
  • 00:05:48
    something in the road is damaged so
  • 00:05:49
    someone comes and digs up the road to
  • 00:05:51
    install something
  • 00:05:52
    and they accidentally slice through a
  • 00:05:54
    load of the cabling
  • 00:05:56
    i might expect that they're just going
  • 00:05:57
    to come along and put another piece of
  • 00:05:58
    this cable in but
  • 00:05:59
    unfortunately it doesn't happen most of
  • 00:06:00
    the time because this old lead covered
  • 00:06:03
    type cable
  • 00:06:03
    pretty much isn't used anymore and all
  • 00:06:06
    the sort of joining equipment they have
  • 00:06:08
    and things
  • 00:06:08
    pretty much isn't up to the standard of
  • 00:06:09
    doing it so if this cable got damaged
  • 00:06:12
    here
  • 00:06:13
    and this could be outside your house or
  • 00:06:15
    banging on it could be a quarter mile
  • 00:06:16
    down the road or in the next street
  • 00:06:17
    where you wouldn't even notice
  • 00:06:19
    then they're gonna have to put in some
  • 00:06:20
    kind of splice here and quite often
  • 00:06:22
    what actually goes in is a piece of
  • 00:06:24
    modern cable and some kind of joint box
  • 00:06:26
    so
  • 00:06:28
    this gets linked through here and then
  • 00:06:30
    the other two
  • 00:06:31
    rather than having a separate cable you
  • 00:06:33
    actually have a single conductor in here
  • 00:06:35
    and it joins onto both of these at both
  • 00:06:38
    ends
  • 00:06:40
    if this is going to be a pme supply
  • 00:06:42
    which is going to be
  • 00:06:43
    there's going to be maybe a
  • 00:06:45
    supplementary electrode installed and
  • 00:06:48
    that goes into the ground between this
  • 00:06:49
    is all very underground anyhow
  • 00:06:52
    and then these parts here are put in
  • 00:06:54
    some sort of enclosure
  • 00:06:57
    resin filled most likely and all is well
  • 00:07:00
    so at your house it still shows up as
  • 00:07:03
    what's tns so the three separate
  • 00:07:04
    conductors
  • 00:07:05
    and for a certain distance outside it
  • 00:07:08
    still is
  • 00:07:09
    but then we've got this repaired section
  • 00:07:10
    here with a new piece of two core cable
  • 00:07:12
    in it
  • 00:07:13
    possibly got a supplemental electrode
  • 00:07:14
    installed as well or maybe not all
  • 00:07:16
    depends on
  • 00:07:17
    who did it and what the individual area
  • 00:07:18
    procedures are
  • 00:07:20
    so even though it's tns here
  • 00:07:24
    it's not because you've now got this
  • 00:07:26
    joined piece here so if something gets
  • 00:07:28
    broken
  • 00:07:28
    along this section you've got exactly
  • 00:07:31
    the same problem as you have on a tn
  • 00:07:32
    cs supply in that if this piece here is
  • 00:07:35
    damaged
  • 00:07:37
    and beyond this could be a few meters
  • 00:07:39
    long or it could be hundreds of meters
  • 00:07:40
    long depending on where it was
  • 00:07:42
    it's just the same as having the link
  • 00:07:44
    there it's just that the link is a bit
  • 00:07:45
    further away but they're still linked
  • 00:07:46
    together
  • 00:07:47
    so line coming in the only earth you've
  • 00:07:51
    got is basically the neutral now
  • 00:07:53
    and all of this part here has a rather
  • 00:07:56
    dangerous voltage on it
  • 00:07:58
    because of course there's no connection
  • 00:07:59
    there anymore just as you'd have if the
  • 00:08:02
    pen conductor or cne conductor on a tncs
  • 00:08:06
    supply it was damaged
  • 00:08:07
    and of course you wouldn't know that
  • 00:08:08
    this had occurred unless you called up
  • 00:08:10
    the uh
  • 00:08:11
    network operator and asked them so what
  • 00:08:14
    might be
  • 00:08:15
    in your house looks like tns quite
  • 00:08:17
    probably isn't
  • 00:08:19
    and this diagram here only shows a
  • 00:08:21
    single repaired piece fairly short
  • 00:08:23
    but if this cable was say 300 meters
  • 00:08:25
    long and a whole section has been
  • 00:08:27
    replaced for some reason
  • 00:08:28
    then of course there could be multiple
  • 00:08:29
    pieces like this or in fact the bulk of
  • 00:08:31
    it could have been replaced with that uh
  • 00:08:33
    two core type cable and you might end up
  • 00:08:36
    with only a little tiny bit
  • 00:08:37
    to your house having the three
  • 00:08:38
    conductors
  • 00:08:40
    the other thing which tends to happen is
  • 00:08:41
    that these old cables get rotten or
  • 00:08:43
    damaged or the connections
  • 00:08:44
    where the joint boxes are rust away and
  • 00:08:47
    rather than
  • 00:08:48
    dig up the whole street to repair those
  • 00:08:49
    things what you'll actually get
  • 00:08:51
    happening
  • 00:08:52
    is that a link will be put in here
  • 00:08:55
    where it's in your house this is then
  • 00:08:58
    tn cs bit to the network might be
  • 00:09:01
    this twin cable or some of it might be
  • 00:09:03
    these so there you get tncs at your
  • 00:09:06
    house
  • 00:09:06
    but by the time they've done that it's
  • 00:09:07
    highly likely that bits of the cabling
  • 00:09:09
    in the street would have been replaced
  • 00:09:10
    with things like this
  • 00:09:12
    this is basically where your pme comes
  • 00:09:15
    from protective multiple earthing
  • 00:09:16
    this being one of them there'll be
  • 00:09:18
    another one back at the transformer and
  • 00:09:19
    possibly others along the network itself
  • 00:09:23
    now another thing to consider is that if
  • 00:09:24
    you've already got a tn
  • 00:09:26
    cs supply which is by far the most
  • 00:09:28
    common now so just two conductors coming
  • 00:09:31
    in
  • 00:09:31
    and the earth is just connected to the
  • 00:09:33
    neutral at the point it comes into the
  • 00:09:35
    property
  • 00:09:36
    nothing else uh obviously there for the
  • 00:09:37
    earth conductor
  • 00:09:39
    you might be tempted to think well we
  • 00:09:40
    could just uh instead of using that
  • 00:09:42
    we'll just convert it to a tt
  • 00:09:43
    system and not use that thing for the
  • 00:09:47
    car charging equipment but there's a
  • 00:09:49
    whole pile of problems here
  • 00:09:50
    as well in the simplest form all you
  • 00:09:52
    would need to do for your charging
  • 00:09:54
    equipment
  • 00:09:55
    is simply not connect it to the earth
  • 00:09:57
    terminal that we have here you would
  • 00:09:59
    just connect the line and neutral
  • 00:10:00
    through
  • 00:10:00
    and then the earth terminal for the
  • 00:10:01
    equipment would be an alert electrode
  • 00:10:04
    poked into the ground now let's say this
  • 00:10:07
    house here wanted to do that
  • 00:10:09
    and i'm going to put our charging piece
  • 00:10:11
    over here on the outside
  • 00:10:13
    so here's our electric vehicle charger
  • 00:10:16
    now of course the charger needs some
  • 00:10:17
    connections to it so you would have the
  • 00:10:18
    wires coming out from the property
  • 00:10:21
    i'm not going to show the protected
  • 00:10:22
    devices here but of course there'll be a
  • 00:10:24
    fuse box and all the other stuff in
  • 00:10:25
    there
  • 00:10:26
    so your neutral come out to that one
  • 00:10:29
    crucially though you wouldn't connect
  • 00:10:31
    the earth terminal here to the earth
  • 00:10:33
    channel in the charging equipment
  • 00:10:35
    you would install your own earth
  • 00:10:37
    electrode in the ground
  • 00:10:40
    and then you would connect the earth
  • 00:10:42
    tone of the charging equipment
  • 00:10:44
    to that and i think well that's fine
  • 00:10:46
    because now
  • 00:10:48
    even if this conductor here gets damaged
  • 00:10:51
    this and the car plugged into it is not
  • 00:10:53
    connected to this
  • 00:10:54
    shared conductor or at least not on the
  • 00:10:56
    actual metal work
  • 00:10:58
    so not gonna be a problem however the
  • 00:11:00
    problem is
  • 00:11:01
    this electrode here where you're
  • 00:11:04
    actually going to put this
  • 00:11:05
    into the ground now a lot of places have
  • 00:11:07
    nice driveways which made of concrete or
  • 00:11:09
    paving or something else so
  • 00:11:11
    in many cases just putting electrode in
  • 00:11:13
    could be a major problem because there
  • 00:11:14
    might not be anywhere obvious to put it
  • 00:11:16
    and once you can dig holes in people's
  • 00:11:17
    driveways and then dig out stuff
  • 00:11:19
    underneath and drive electrodes down
  • 00:11:20
    underneath and attempt to make some kind
  • 00:11:21
    of repair
  • 00:11:22
    not really the best choice there but
  • 00:11:25
    rather more importantly
  • 00:11:26
    where you're going to put your electrode
  • 00:11:28
    it has to be a decent distance away
  • 00:11:31
    from anything else that's buried
  • 00:11:32
    underground and things that are buried
  • 00:11:35
    underground
  • 00:11:35
    there's a whole pile of stuff such as
  • 00:11:38
    cables
  • 00:11:40
    most importantly the cables that come
  • 00:11:41
    into the house and supply it with
  • 00:11:42
    electricity
  • 00:11:44
    and everything else such as gas pipes
  • 00:11:47
    water pipes
  • 00:11:48
    and in fact anything else that's
  • 00:11:50
    underground now apart from the risk of
  • 00:11:51
    just driving a stake right through these
  • 00:11:53
    and causing them to be damaged and then
  • 00:11:54
    you've got gas leaks and fires and who
  • 00:11:56
    knows what
  • 00:11:58
    you can't put an electrode near
  • 00:12:01
    to any of these items now how far away
  • 00:12:03
    it can be from underground cables those
  • 00:12:05
    supplying the electricity to your house
  • 00:12:06
    does vary
  • 00:12:07
    but in many cases you're looking at the
  • 00:12:09
    distances of around five meters
  • 00:12:12
    and in many cases considerably more than
  • 00:12:14
    that and if you think about the width of
  • 00:12:15
    an average house
  • 00:12:16
    that could either be the width of your
  • 00:12:18
    typical certainly a terraced house or a
  • 00:12:19
    semi-detached
  • 00:12:21
    so getting the electrode five meters
  • 00:12:22
    away from the incoming supply cable
  • 00:12:25
    may be entirely impossible the other
  • 00:12:27
    thing to consider is that you can't put
  • 00:12:28
    it near any metallic pipes on the ground
  • 00:12:30
    because
  • 00:12:31
    if you had some gas pipes underground
  • 00:12:34
    let's draw those in here they would go
  • 00:12:35
    into the property
  • 00:12:37
    and they're going to go into the next
  • 00:12:38
    property and of course they're going to
  • 00:12:40
    go all the way along the street
  • 00:12:42
    to the next property and so on within
  • 00:12:45
    the properties here
  • 00:12:46
    all these gas pipes are going to have a
  • 00:12:48
    bond that goes over to the earthing
  • 00:12:50
    terminal
  • 00:12:50
    and it's going to be the same in this
  • 00:12:52
    house over here and obviously all the
  • 00:12:54
    ones down the street
  • 00:12:55
    if you put your electrode in the ground
  • 00:12:57
    and it happens to be nearby
  • 00:12:58
    one of these gas pipes or water pipes or
  • 00:13:01
    whatever else
  • 00:13:02
    when a fault occurs and this conductor
  • 00:13:04
    has broken
  • 00:13:06
    this blue one here is the one that has a
  • 00:13:09
    dangerous voltage on it but of course
  • 00:13:10
    it's also connected to the main earth
  • 00:13:11
    terminal
  • 00:13:12
    and it's also connected to this gas or
  • 00:13:14
    water pipe that's on the ground so if
  • 00:13:16
    your electrode is there
  • 00:13:17
    then it's even within a few meters of
  • 00:13:19
    the underground gas pipe
  • 00:13:21
    that voltage would transfer onto this
  • 00:13:23
    electrode
  • 00:13:24
    and then you've got the exact same
  • 00:13:25
    problem you would have had before it's
  • 00:13:27
    slightly better because it's not in
  • 00:13:28
    direct contact
  • 00:13:30
    but there's still that high likelihood
  • 00:13:31
    of a dangerous voltage appearing on this
  • 00:13:33
    appearing on the outside of the charging
  • 00:13:35
    thing if it's metal and definitely
  • 00:13:36
    appearing on the
  • 00:13:37
    external metal work of your car that's
  • 00:13:39
    plugged into this
  • 00:13:41
    so if you're going to convert it to a tt
  • 00:13:43
    this has to be many meters away
  • 00:13:46
    from anything under the ground gas water
  • 00:13:49
    any kind of other metallic pipes and
  • 00:13:50
    things that are connected to the
  • 00:13:51
    earthing terminal
  • 00:13:52
    and in most cases that's going to be
  • 00:13:54
    next to impossible to achieve
  • 00:13:57
    now here's another scenario two houses
  • 00:14:00
    each have an electric car charging point
  • 00:14:02
    and it's a shared space in the middle so
  • 00:14:03
    it's divided up into the two halves but
  • 00:14:05
    it's pretty much the same open area
  • 00:14:07
    just happens to be the width of a couple
  • 00:14:09
    of vehicles plus a bit of space
  • 00:14:10
    and there might be sort of a thin line
  • 00:14:12
    of vent or something down the middle
  • 00:14:13
    so charging box and electric vehicle
  • 00:14:15
    charging box and another electric
  • 00:14:17
    vehicle
  • 00:14:18
    now if one of these houses had converted
  • 00:14:19
    itself to be a tt installation
  • 00:14:22
    i'd say it was the end one because it
  • 00:14:23
    had a big field over to the side there
  • 00:14:25
    so
  • 00:14:25
    it could actually put the electrode in
  • 00:14:26
    out of sight way over here
  • 00:14:29
    so it was a considerable distance away
  • 00:14:30
    from anything else and then of course
  • 00:14:32
    that was linked in
  • 00:14:33
    and went over to the charging point and
  • 00:14:35
    i didn't use the other one for that
  • 00:14:37
    then tt installation here if this one
  • 00:14:40
    over here
  • 00:14:41
    is not they just decided to have it be
  • 00:14:43
    done on the cheap and they had a
  • 00:14:45
    tn cs connection there and somebody just
  • 00:14:47
    didn't bother with it or they put just a
  • 00:14:49
    uh
  • 00:14:49
    a 13 amp plug on the outside wall and
  • 00:14:52
    plugged it into that thinking that was a
  • 00:14:53
    good idea
  • 00:14:54
    when the fault occurs and this conductor
  • 00:14:56
    here gets busted
  • 00:14:58
    all of the blue here becomes a dangerous
  • 00:14:59
    voltage that means that this
  • 00:15:02
    particular vehicle here will have a
  • 00:15:04
    dangerous voltage on it
  • 00:15:05
    relative to the earth itself and even
  • 00:15:08
    worse than this
  • 00:15:09
    the voltage between these two parked
  • 00:15:12
    cars will now be considerable because
  • 00:15:14
    this one is connected to the earth from
  • 00:15:16
    the
  • 00:15:16
    tncs service and this one is connected
  • 00:15:19
    directly into the earth itself with an
  • 00:15:21
    electrode far away from these so
  • 00:15:23
    guaranteed to be a much lower voltage
  • 00:15:24
    than this one and of course these cars
  • 00:15:26
    close together
  • 00:15:27
    they can be touched at the same time
  • 00:15:29
    you've got a couple of hundred volts
  • 00:15:31
    between them
  • 00:15:32
    people are going to get shocked and
  • 00:15:33
    injured and this can even happen with a
  • 00:15:36
    single house so if you had your car
  • 00:15:38
    charging away on the driveway there with
  • 00:15:40
    its two wheels
  • 00:15:42
    and the charging box was here if your
  • 00:15:44
    charging box is connected to an earth
  • 00:15:46
    electrode so it's put in the ground and
  • 00:15:48
    we managed to get it away from the other
  • 00:15:49
    pipes and all the other problems
  • 00:15:52
    if you've got say an outside light on
  • 00:15:53
    your house
  • 00:15:56
    like that and that light happens to be
  • 00:15:58
    connected through to the
  • 00:16:01
    supply provided there from the ts supply
  • 00:16:03
    when this fault occurs where you've got
  • 00:16:05
    this break in the
  • 00:16:06
    conductor there all of the blue becomes
  • 00:16:09
    at a dangerous voltage 200 volts or
  • 00:16:10
    something like that
  • 00:16:12
    but of course the vehicle isn't because
  • 00:16:14
    it's connected via the
  • 00:16:15
    system here so then between the vehicle
  • 00:16:17
    and the outside light
  • 00:16:19
    there's your dangerous voltage so if
  • 00:16:22
    you're going to make it tt
  • 00:16:24
    you can't have any other items on the
  • 00:16:25
    outside of the building here
  • 00:16:27
    that are connected to the earth provided
  • 00:16:29
    by the supplier
  • 00:16:30
    because otherwise when the fault occurs
  • 00:16:32
    you're getting that dangerous voltage
  • 00:16:34
    between those objects
  • 00:16:36
    and it might not even have to be a light
  • 00:16:38
    fixture
  • 00:16:39
    it could be something as simple as an
  • 00:16:41
    outside tap
  • 00:16:42
    because if you've got an outside tap
  • 00:16:44
    because it's going to come from the
  • 00:16:45
    water pipe here
  • 00:16:47
    just draw it in there and imagine that's
  • 00:16:49
    a tap it's connected to the water supply
  • 00:16:52
    which again goes through the street and
  • 00:16:53
    of course within the house
  • 00:16:56
    that supply is going to be bonded to the
  • 00:16:58
    incoming
  • 00:16:59
    earth terminal so just as before
  • 00:17:03
    your car is sitting there connected to
  • 00:17:05
    the charging point
  • 00:17:06
    and then between your outside tap and
  • 00:17:08
    the charging unit
  • 00:17:09
    you've got a dangerous voltage straight
  • 00:17:11
    away and there's even one manufacturer
  • 00:17:13
    that makes
  • 00:17:14
    an outside charging point where you can
  • 00:17:15
    have a outside tap put in the bottom of
  • 00:17:17
    it as well
  • 00:17:18
    so ridiculous so again a really
  • 00:17:21
    ridiculous situation
  • 00:17:22
    so changing any kind of existing station
  • 00:17:24
    to
  • 00:17:25
    tt is a pile of problems and not really
  • 00:17:29
    something you want to be doing
  • 00:17:30
    as yes the car itself might be safe in
  • 00:17:33
    isolation
  • 00:17:34
    but combined all the other stuff that's
  • 00:17:35
    around there it most definitely isn't
  • 00:17:38
    and the final point with changing order
  • 00:17:39
    t2 you might be considering or tempted
  • 00:17:41
    to instead of doing
  • 00:17:42
    all that bother with the different
  • 00:17:43
    exposed parts and different voltages and
  • 00:17:45
    all that hassle
  • 00:17:46
    i think well why don't we just not
  • 00:17:47
    bother with this tncs supply whatsoever
  • 00:17:50
    just throw it all away and why don't we
  • 00:17:51
    just convert the whole house to a tt
  • 00:17:53
    supply instead because
  • 00:17:55
    again that is an option which you could
  • 00:17:56
    use so if you're gonna do that first of
  • 00:17:58
    all you need to put earth electrode
  • 00:18:00
    somewhere suitable so you can't put it
  • 00:18:01
    obviously in the way of things under the
  • 00:18:03
    ground or anything like that so you'd
  • 00:18:04
    have to put it far away in the back
  • 00:18:05
    garden
  • 00:18:06
    at some considerable distance but let's
  • 00:18:09
    say that we did actually do that so
  • 00:18:11
    let's put the electrode way over there
  • 00:18:14
    in the back garden in a field or
  • 00:18:15
    something like that so it's well away
  • 00:18:16
    from anything else
  • 00:18:17
    buried in the ground and then we're not
  • 00:18:20
    going to have
  • 00:18:22
    this supplier's earth used at all we're
  • 00:18:25
    just going to leave that disconnected
  • 00:18:26
    there
  • 00:18:27
    and then this coming in will be the
  • 00:18:30
    real earth that we're going to be using
  • 00:18:33
    and that will be a tt arrangement
  • 00:18:35
    absolutely fine
  • 00:18:37
    but just to make it no it isn't
  • 00:18:38
    absolutely fine because yes there's
  • 00:18:40
    another problem here as well if you've
  • 00:18:42
    got metal pipes coming into your house
  • 00:18:44
    from the gas and water and whatever
  • 00:18:46
    other services you may have in your area
  • 00:18:48
    if these pipes are metal and they're
  • 00:18:49
    coming into your house
  • 00:18:51
    this pipe here is connected to everybody
  • 00:18:54
    else's house in the street and in the
  • 00:18:55
    house over here
  • 00:18:56
    where that pipe comes into their house
  • 00:18:58
    and goes to the various parts of the
  • 00:18:59
    building
  • 00:19:01
    of course they're going to have their
  • 00:19:02
    main bonding installed which comes
  • 00:19:04
    across
  • 00:19:05
    to the combined earth and neutral
  • 00:19:07
    terminal there and that's a metallic
  • 00:19:09
    path all the way through into your house
  • 00:19:11
    and of course the next house down the
  • 00:19:12
    road and all the others in the street
  • 00:19:15
    so if this is coming into your house and
  • 00:19:17
    of course regulations require that uh
  • 00:19:19
    metallic parts coming in
  • 00:19:20
    are bonded so you put your bonding
  • 00:19:22
    conductor in like this
  • 00:19:24
    from your main earth terminal to the
  • 00:19:26
    state water pipe
  • 00:19:28
    is this now really a tt system
  • 00:19:33
    and the answer is no it isn't because
  • 00:19:35
    what you've now got
  • 00:19:37
    is the potential from the tncs or the
  • 00:19:40
    pme earth coming in
  • 00:19:42
    via this water pipe from next door and
  • 00:19:44
    next door and so on
  • 00:19:45
    and being made of metal that's going to
  • 00:19:46
    be a very low resistance
  • 00:19:48
    far lower than any earth rod stuck in a
  • 00:19:50
    field ever will be so what you've now
  • 00:19:52
    got here
  • 00:19:53
    is not tt anymore it's actually
  • 00:19:56
    a tncs with an extra electrode installed
  • 00:20:01
    now the extra electrode may help in the
  • 00:20:03
    situation where the conductor is broken
  • 00:20:06
    all of this becomes a dangerous voltage
  • 00:20:08
    because it's giving a bit of an extra
  • 00:20:09
    connection
  • 00:20:10
    to the earth there but in reality it's
  • 00:20:13
    not going to have a huge impact
  • 00:20:15
    that becomes a dangerous voltage as
  • 00:20:17
    we've seen before because it's all
  • 00:20:18
    connected through
  • 00:20:19
    at the same point here live go to
  • 00:20:22
    appliances
  • 00:20:23
    comes to all those comes back on there
  • 00:20:24
    so it's got nowhere to go
  • 00:20:26
    so in terms of what's dangerous here all
  • 00:20:28
    of this conductor here
  • 00:20:30
    and pretty much anything else that's
  • 00:20:31
    connected to it so the metal pipes come
  • 00:20:34
    in your house and your neighbors
  • 00:20:36
    is bringing that dangerous potential
  • 00:20:37
    into your property
  • 00:20:39
    and then of course it's going to go on
  • 00:20:40
    to things that are connected to outside
  • 00:20:41
    like your car charging point
  • 00:20:43
    the outside tap that solves the metal
  • 00:20:46
    pipe going straight to it
  • 00:20:47
    so not really a tt system so the only
  • 00:20:50
    way you can do it
  • 00:20:51
    if you've got that is to replace these
  • 00:20:54
    pipes here
  • 00:20:55
    with plastic and that includes things
  • 00:20:58
    like your gas pipe which you can't
  • 00:20:59
    really do with plastic unless it's
  • 00:21:00
    already plastic in the ground
  • 00:21:02
    plastic water pipes and have no
  • 00:21:04
    connection whatsoever
  • 00:21:05
    to any other metallic parts from
  • 00:21:08
    adjoining properties
  • 00:21:10
    and on top of that you still need to
  • 00:21:11
    make sure that your earth electrode or
  • 00:21:13
    electrodes or maps or whatever
  • 00:21:14
    are a decent distance away from all of
  • 00:21:16
    this buried underground stuff
  • 00:21:18
    as we saw previously if you put this
  • 00:21:20
    anywhere near anything underground it's
  • 00:21:22
    going to pick up a voltage from this
  • 00:21:23
    when the fault occurs
  • 00:21:24
    and again bring that dangerous potential
  • 00:21:26
    into your property and onto your
  • 00:21:28
    cart charging point so in reality then
  • 00:21:31
    what are your options so a tt system
  • 00:21:33
    already
  • 00:21:34
    that's probably the best and that's all
  • 00:21:35
    you can use because if it's tt already
  • 00:21:38
    that's all you've got
  • 00:21:39
    if it's the tns
  • 00:21:43
    probably not and the reason being that
  • 00:21:45
    it's almost going to be
  • 00:21:47
    a tn cs in disguise and then of course
  • 00:21:50
    that's the one where you have the
  • 00:21:52
    problems because it's not
  • 00:21:55
    suitable to use when the protective
  • 00:21:56
    contact gets damaged and that's where
  • 00:21:58
    you have dangerous voltages outside
  • 00:22:00
    and that thing is entirely why things
  • 00:22:01
    like caravans can't have a pma supply
  • 00:22:04
    either
  • 00:22:04
    that's exactly the same reason and why
  • 00:22:06
    it's definitely not recommended things
  • 00:22:07
    like swimming pools
  • 00:22:08
    hot tubs and other things that are
  • 00:22:10
    outside so if you've got a tt
  • 00:22:12
    installation in your house already and
  • 00:22:13
    that's what it's been forever
  • 00:22:15
    then that's really the best situation
  • 00:22:17
    tncs is probably not tns
  • 00:22:19
    because it's almost certainly going to
  • 00:22:20
    be converted to tn at cs
  • 00:22:22
    and then of course that's where the
  • 00:22:23
    problems occur and that's when we have
  • 00:22:25
    those five
  • 00:22:26
    options in the regulations which you can
  • 00:22:29
    allegedly use to mitigate the problem
  • 00:22:31
    when
  • 00:22:31
    the conductor is broken so let's just
  • 00:22:34
    have a look at those five
  • 00:22:35
    and see if they're actually any good now
  • 00:22:38
    in section 72 the
  • 00:22:40
    regulation is 7241141
  • 00:22:43
    and this refers to a tn system and it
  • 00:22:46
    basically says a pme earthing facility
  • 00:22:47
    shall not be used as the means of
  • 00:22:49
    earthing for the protective inductor
  • 00:22:50
    contact of a charging point located
  • 00:22:52
    outdoors or that might be reasonably
  • 00:22:54
    expected to be used to charge a vehicle
  • 00:22:56
    located outdoors
  • 00:22:57
    unless one of the following methods is
  • 00:22:58
    used now in reality
  • 00:23:00
    vehicles are going to be charged
  • 00:23:01
    outdoors because that's where people put
  • 00:23:03
    them
  • 00:23:03
    so there's very few instances where you
  • 00:23:05
    would have that on the say an indoor
  • 00:23:07
    charging arrangement
  • 00:23:09
    and this is the thing with the five
  • 00:23:10
    options now the first option
  • 00:23:12
    being number one is where you have a
  • 00:23:15
    charging point that forms part of a
  • 00:23:16
    three-phase installation
  • 00:23:18
    and this is where it supplies loads
  • 00:23:19
    other than electric vehicle charging and
  • 00:23:21
    because of the type installation
  • 00:23:23
    the maximum voltage is going to exceed
  • 00:23:25
    70 volts now
  • 00:23:26
    this is never going to be used in a
  • 00:23:27
    domestic installation simply the fact
  • 00:23:30
    that domestic installations
  • 00:23:31
    don't have three phase so of course
  • 00:23:33
    that's out the window completely
  • 00:23:35
    and even if you're in a situation that
  • 00:23:36
    did as we've covered in other videos
  • 00:23:38
    the likelihood of having an installation
  • 00:23:40
    where the loads on it are always going
  • 00:23:42
    to be decently balanced
  • 00:23:43
    is pretty much zero anyhow so that
  • 00:23:46
    option is usually a fail
  • 00:23:48
    and certainly as a fail on domestic
  • 00:23:49
    where you've only got single phase
  • 00:23:50
    available
  • 00:23:51
    option number two is quite an
  • 00:23:53
    interesting one which we'll actually
  • 00:23:54
    come back to
  • 00:23:55
    and look at at the end because it may
  • 00:23:57
    end up being the actual proper solution
  • 00:23:59
    in the final scheme of things although
  • 00:24:01
    you may not like the price of
  • 00:24:02
    actually doing it now the other three
  • 00:24:05
    are the various devices which may or may
  • 00:24:09
    not exist and some manufacturers claim
  • 00:24:10
    to have them and others don't and
  • 00:24:12
    some of them may never exist so the
  • 00:24:14
    first device is number three there
  • 00:24:16
    protection against later shock is
  • 00:24:17
    provided by this device this is the one
  • 00:24:19
    that monitors the voltage
  • 00:24:21
    and it's the voltage between the earth
  • 00:24:24
    of the installation
  • 00:24:26
    and the actual earth
  • 00:24:30
    which means it's going to be outside and
  • 00:24:32
    if this exceeds 70 volts
  • 00:24:34
    for more than four seconds then it will
  • 00:24:35
    disconnect the equipment and crucially
  • 00:24:37
    disconnect the
  • 00:24:39
    installation earth as well because
  • 00:24:40
    that's where your dangerous voltage will
  • 00:24:41
    appear
  • 00:24:43
    all very well in theory however the
  • 00:24:44
    problem with this is that to detect the
  • 00:24:46
    voltage between two parts
  • 00:24:48
    you've got this already but to take the
  • 00:24:50
    voltage between that and the actual
  • 00:24:51
    earth outside you're going to need some
  • 00:24:52
    kind of earth electrode to be put in
  • 00:24:54
    because there's no other way you can
  • 00:24:55
    measure voltage between two items you've
  • 00:24:57
    got to have a connection to them
  • 00:24:59
    and whether this is going to be an
  • 00:25:00
    actual electrode or some kind of thin
  • 00:25:02
    probe as some manufacturer may have
  • 00:25:03
    suggested the reality is going to have
  • 00:25:05
    to shove something in the ground
  • 00:25:06
    and then straight away back to all those
  • 00:25:08
    problems we had before where
  • 00:25:10
    electrode or probe or sensor whatever
  • 00:25:12
    else it is going in the ground
  • 00:25:13
    there's got to be many many meters away
  • 00:25:16
    from anything else in the ground like
  • 00:25:17
    pipes cables or whatever else
  • 00:25:19
    you've got to make sure that it's
  • 00:25:20
    obviously not going to be poking through
  • 00:25:21
    anything else in there
  • 00:25:22
    it's all the same problems as a tt
  • 00:25:24
    installation so of course why would you
  • 00:25:26
    actually bother
  • 00:25:27
    the only difference is that you're
  • 00:25:28
    having the earth and they need an extra
  • 00:25:30
    bit of machinery to connect between it
  • 00:25:31
    so
  • 00:25:32
    that really is a bit of a bust and
  • 00:25:33
    that's one that's called this unicorn
  • 00:25:35
    device which uh
  • 00:25:36
    theoretically exists from these one
  • 00:25:38
    manufacturer but again why would you
  • 00:25:40
    bother when you can just make it a tt if
  • 00:25:41
    you're going to go to what hassle of
  • 00:25:42
    having electrodes
  • 00:25:44
    now number four is protection against
  • 00:25:47
    electric shock in the single phase
  • 00:25:48
    installation
  • 00:25:49
    is by another device and this one
  • 00:25:51
    monitors the voltage
  • 00:25:52
    between the line and neutral conductors
  • 00:25:56
    and if the voltage goes outside of a
  • 00:25:57
    certain range which is based in the
  • 00:25:59
    normal range which is 207
  • 00:26:01
    to 253 volts then it will disconnect
  • 00:26:05
    and also of course remove that
  • 00:26:06
    protective conductor as well
  • 00:26:09
    now if the pen conductor is broken
  • 00:26:13
    in some cases yes the voltage will go
  • 00:26:15
    either lower than this
  • 00:26:17
    or higher than that the problem here is
  • 00:26:19
    that it doesn't do that in
  • 00:26:20
    all cases and this is due with a
  • 00:26:23
    three-phase system
  • 00:26:24
    becoming unbalanced and whilst your
  • 00:26:26
    house doesn't have a three-phase system
  • 00:26:28
    the connection to it from the street
  • 00:26:29
    almost certainly will be a three-phase
  • 00:26:31
    system
  • 00:26:32
    and in some cases some houses are going
  • 00:26:35
    to get a high voltage
  • 00:26:36
    some of them will get a low voltage but
  • 00:26:38
    it's totally possible for some to have
  • 00:26:39
    voltage that's within this range
  • 00:26:42
    that's between a line of neutral but
  • 00:26:44
    crucially between
  • 00:26:46
    what you might think is the neutral and
  • 00:26:47
    then the earth outside
  • 00:26:49
    that can still be more than 70 volts
  • 00:26:53
    because what's then happened is that
  • 00:26:54
    both of these have gone up
  • 00:26:57
    relative to the earth here so the
  • 00:27:00
    difference between them is still within
  • 00:27:01
    this boundary
  • 00:27:02
    but because they're both lifted they're
  • 00:27:04
    now both considerably above the
  • 00:27:06
    actual earth outside and if that's more
  • 00:27:08
    than 70 volts then again there's your
  • 00:27:09
    problem
  • 00:27:10
    dangerous shocks and whatever else are
  • 00:27:12
    going to happen
  • 00:27:13
    so that in itself may work in some
  • 00:27:15
    situations but it most certainly won't
  • 00:27:17
    work in all of them
  • 00:27:18
    so yeah not really a particularly
  • 00:27:21
    desirable result
  • 00:27:23
    and then number five is some other
  • 00:27:25
    device which isn't really defined in the
  • 00:27:26
    regulations at all
  • 00:27:28
    it's an alternative device that doesn't
  • 00:27:30
    result in a lesser degree of safety from
  • 00:27:31
    the two devices mentioned earlier now
  • 00:27:34
    as far as i can see there aren't any
  • 00:27:35
    devices on the market which would do
  • 00:27:37
    that
  • 00:27:38
    because it does state it doesn't provide
  • 00:27:40
    a lesser degree of safety than using
  • 00:27:42
    three or four now
  • 00:27:45
    lesser degree of safety than three means
  • 00:27:47
    it's going to have to do at least what
  • 00:27:48
    number three would do and that's where
  • 00:27:49
    you've got a sense in the actual ground
  • 00:27:51
    itself that will work in all cases
  • 00:27:53
    but nobody's going to install that
  • 00:27:54
    because you need to put another
  • 00:27:55
    electrode in
  • 00:27:56
    better than four there is one way of
  • 00:27:59
    doing it
  • 00:28:00
    and certainly one matter at least has
  • 00:28:01
    this and essentially what it does it's a
  • 00:28:03
    voltage monitoring device
  • 00:28:05
    which is just the same as we had in
  • 00:28:06
    number four and that's again between
  • 00:28:08
    that range of voltages
  • 00:28:09
    as stated in the regulations it's the
  • 00:28:11
    207 to 253.
  • 00:28:14
    obviously manufacturers may choose a
  • 00:28:15
    slightly different range if they deem
  • 00:28:17
    that appropriate
  • 00:28:18
    and then what at least one of them has
  • 00:28:19
    got is a sense
  • 00:28:21
    coil similar to an rcd
  • 00:28:25
    so i've got a magnetic core there with
  • 00:28:27
    the sense wires coming off of that
  • 00:28:29
    what goes through this
  • 00:28:32
    is the protective conductor that goes to
  • 00:28:34
    the charging equipment so
  • 00:28:36
    here would be your electric car
  • 00:28:40
    all the wires going through and that
  • 00:28:43
    protective conductor coming through
  • 00:28:45
    there
  • 00:28:46
    let's draw that in green that's a bit
  • 00:28:47
    more obvious
  • 00:28:49
    what it's doing is monitoring the
  • 00:28:50
    current that flowed through this
  • 00:28:51
    protective conductor
  • 00:28:53
    now in normal cases there shouldn't be
  • 00:28:54
    any current going through there so if it
  • 00:28:56
    detects that there's current flowing
  • 00:28:57
    through this
  • 00:28:58
    electronics in the device will then
  • 00:29:00
    disconnect all of the conductors to it
  • 00:29:02
    and therefore remove that danger from it
  • 00:29:04
    so basically it's going to cut that off
  • 00:29:05
    completely
  • 00:29:05
    leaving it totally isolated now that
  • 00:29:08
    sounds like a good idea in theory
  • 00:29:10
    but unfortunately there's a problem with
  • 00:29:11
    this
  • 00:29:13
    cars have rubber tyres and they're
  • 00:29:15
    generally insulated from the ground that
  • 00:29:17
    they're standing on
  • 00:29:19
    so if a dangerous voltage occurs on this
  • 00:29:21
    conductor initially nothing will happen
  • 00:29:24
    the only time something's going to
  • 00:29:25
    happen is if some unfortunate individual
  • 00:29:27
    was standing here next to the electric
  • 00:29:30
    car
  • 00:29:32
    and if they touch the car where's the
  • 00:29:34
    current going to flow well it's going to
  • 00:29:35
    go through the
  • 00:29:37
    sensing coil here through the car and
  • 00:29:39
    then through the person and into
  • 00:29:41
    of course the ground or earth down here
  • 00:29:45
    and then that will disconnect and all
  • 00:29:46
    this well but not really because it's
  • 00:29:48
    already put the current through the
  • 00:29:49
    person and giving them a fairly
  • 00:29:50
    unpleasant shock
  • 00:29:51
    now while this is better than nothing
  • 00:29:53
    it's unfortunately not good enough
  • 00:29:55
    because
  • 00:29:56
    this is equivalent to using an rcd as a
  • 00:29:58
    single means of protection so basically
  • 00:30:01
    stuff sits around being live when
  • 00:30:03
    someone grabs hold of it it might
  • 00:30:04
    disconnect
  • 00:30:05
    and that's similar to if you've had your
  • 00:30:06
    house with the lighting circuit with no
  • 00:30:08
    protective conductor in it you can't
  • 00:30:10
    just bung an rcd on and hold it all this
  • 00:30:12
    well because you've got metal items
  • 00:30:13
    there because then
  • 00:30:14
    again it would sit there doing nothing
  • 00:30:15
    with live parts hanging down live
  • 00:30:17
    switches
  • 00:30:18
    when some person came along and touched
  • 00:30:19
    it they get a shock and then the thing
  • 00:30:21
    disconnects
  • 00:30:22
    and the regulator's question is four one
  • 00:30:23
    five one two which states that the use
  • 00:30:26
    of rcds is not recognized as a solid
  • 00:30:28
    protection
  • 00:30:28
    and does not obviate the need to apply
  • 00:30:29
    when the protected measures specified in
  • 00:30:31
    four one four and four which are all the
  • 00:30:32
    usual
  • 00:30:34
    automatic disconnection supply and so on
  • 00:30:36
    now whilst the device in the charging
  • 00:30:38
    point is not technically an rcd because
  • 00:30:40
    it's sensing on a single conductor only
  • 00:30:43
    the reality is that the principle is the
  • 00:30:44
    same you don't want a system which
  • 00:30:46
    requires people to get a shock before it
  • 00:30:48
    actually disconnects you want to happen
  • 00:30:50
    obviously well in advance of that and
  • 00:30:52
    then that comes back to having a probe
  • 00:30:53
    in the ground to detect the voltage
  • 00:30:54
    between the actual earth
  • 00:30:56
    and the conductors in the installation
  • 00:30:57
    which again is the same
  • 00:30:59
    effort and bother that's putting in a tt
  • 00:31:01
    installation in the first place
  • 00:31:04
    so what then is the answer well the
  • 00:31:06
    answer is certainly with the regulations
  • 00:31:07
    we currently have them
  • 00:31:09
    is the second item out of those five
  • 00:31:11
    which states the main i think terminal
  • 00:31:13
    the installation is connected to an
  • 00:31:14
    installation of electrode by a
  • 00:31:15
    protective conductor
  • 00:31:16
    and the resistance of the earth
  • 00:31:17
    electrode to earth shall we search that
  • 00:31:19
    the maximum voltage between the main
  • 00:31:20
    earthing terminal the installation and
  • 00:31:22
    earth in the event of an open circuit
  • 00:31:23
    fault in the pen conductor
  • 00:31:25
    and so on does not exceed 70 volts
  • 00:31:28
    so what this means then if you've got
  • 00:31:29
    your house
  • 00:31:32
    and it has a tn cs supply which let's
  • 00:31:34
    face it uh
  • 00:31:35
    most of them obviously will it's sitting
  • 00:31:38
    on the ground there
  • 00:31:41
    we'll put the suppliers coming in and of
  • 00:31:44
    course your earth is then just provided
  • 00:31:45
    as
  • 00:31:46
    a connection from that particular
  • 00:31:48
    conductor
  • 00:31:49
    what this means is that when this
  • 00:31:51
    conductor is damaged a dangerous voltage
  • 00:31:53
    is going to occur here
  • 00:31:54
    and the way to reduce this voltage is to
  • 00:31:56
    connect this
  • 00:31:57
    to an additional earth electrode that
  • 00:32:00
    you've got outside of your house
  • 00:32:02
    now the problem with putting a single
  • 00:32:03
    electrode in is you're going to have a
  • 00:32:04
    fairly high resistance in the soil or
  • 00:32:06
    whatever
  • 00:32:06
    if you can get less than 100 ohms with a
  • 00:32:08
    single one then you're doing pretty well
  • 00:32:10
    and this particular regulation there is
  • 00:32:11
    a part in the annex
  • 00:32:13
    in section 722 and this gives you some
  • 00:32:16
    examples and if you do the calculations
  • 00:32:18
    you want something in the region
  • 00:32:20
    of 5 ohms or less
  • 00:32:23
    perhaps in the case of 2 ohms or less
  • 00:32:27
    now if you want to sting electrode in
  • 00:32:30
    you're not going to be getting anywhere
  • 00:32:31
    near that so how can it be done well the
  • 00:32:33
    answer is you don't put it in a single
  • 00:32:35
    stick in the ground
  • 00:32:36
    what you do is you dig up the person's
  • 00:32:38
    driveway like that
  • 00:32:41
    and inside the ground before you put
  • 00:32:42
    your driveway in you put a big mesh
  • 00:32:45
    or grid of tape this could be that
  • 00:32:48
    reinforcement fabric you can buy for
  • 00:32:49
    putting in concrete or whatever
  • 00:32:51
    and that goes in there under the
  • 00:32:52
    driveway over an area of say
  • 00:32:55
    10 or 20 square meters so once that's
  • 00:32:58
    inside
  • 00:32:59
    and it's being installed you have your
  • 00:33:00
    concrete put over the top or whatever
  • 00:33:02
    nice surface you're having tarmac or
  • 00:33:03
    paving slabs or whatever else
  • 00:33:06
    before that's done you need to have a
  • 00:33:07
    connection made to that metal work
  • 00:33:08
    underground
  • 00:33:10
    that goes inside and connects to the
  • 00:33:11
    main earth terminal in the building
  • 00:33:13
    so once it's all finished and covered
  • 00:33:14
    over it looks exactly the same
  • 00:33:16
    but all this metal work buried
  • 00:33:18
    underground it's going to have a massive
  • 00:33:19
    surface area compared to that tiny
  • 00:33:21
    little rod you might have stuck in for a
  • 00:33:22
    tt installation so its
  • 00:33:24
    resistance there is going to be much
  • 00:33:25
    lower that's how you get it in this
  • 00:33:27
    single digit ohm range
  • 00:33:29
    and then when this conductor becomes
  • 00:33:31
    damaged and broken
  • 00:33:33
    although the voltage on this thing would
  • 00:33:35
    normally go fairly high because it's
  • 00:33:37
    connected to the earth here
  • 00:33:39
    very solidly that will keep the voltage
  • 00:33:41
    here much lower
  • 00:33:42
    what will actually happen is that the
  • 00:33:44
    current in the installation
  • 00:33:46
    which will be from your line connectors
  • 00:33:49
    to your appliances in the house
  • 00:33:51
    and then coming back if that was totally
  • 00:33:54
    open you get 230 volts here
  • 00:33:56
    because it's got a decent path going
  • 00:33:58
    back to the earth here of a low
  • 00:34:00
    resistance a couple of ohms it's got
  • 00:34:02
    somewhere for the current to flow
  • 00:34:04
    go back into the ground eventually gets
  • 00:34:05
    back to the transformer so the voltage
  • 00:34:07
    here
  • 00:34:08
    is kept down at a decent level and in
  • 00:34:11
    this case your vehicle
  • 00:34:13
    sitting on the driveway there connected
  • 00:34:16
    to this
  • 00:34:18
    voltage difference between the vehicle
  • 00:34:20
    itself and exposed metal parts
  • 00:34:22
    and the ground itself with this massive
  • 00:34:24
    metal grid in
  • 00:34:25
    is going to be fairly small and
  • 00:34:27
    certainly well under
  • 00:34:28
    the 70 volts there
  • 00:34:32
    that's required in the regulations now
  • 00:34:34
    this is totally permitted and it's
  • 00:34:35
    actually suggested in that section two
  • 00:34:38
    connecting your own electrode to a tncs
  • 00:34:41
    provided earth
  • 00:34:41
    is also permitted and has been pretty
  • 00:34:43
    much forever most people should not do
  • 00:34:45
    it because in most cases a single rod is
  • 00:34:47
    useless
  • 00:34:48
    but if you've got a big section like
  • 00:34:50
    this then it's absolutely ideal
  • 00:34:52
    and the other way it could be done if
  • 00:34:53
    you're going to be building a new house
  • 00:34:54
    for example
  • 00:34:55
    is when you're building the house and
  • 00:34:57
    putting in the concrete foundations
  • 00:34:58
    which might be say a
  • 00:35:00
    strip foundation for example if when the
  • 00:35:03
    house was built
  • 00:35:04
    they put in a load of reinforcement
  • 00:35:06
    fabric in here
  • 00:35:08
    and also in here and had the good sense
  • 00:35:11
    to make it exposed here so it could
  • 00:35:13
    connect to the main earthing terminal
  • 00:35:14
    then you've got again this massive
  • 00:35:16
    section all the way under the house
  • 00:35:17
    there
  • 00:35:18
    huge surface area connecting to the
  • 00:35:19
    actual earth itself and again
  • 00:35:21
    you could use that and if it was a raft
  • 00:35:24
    type foundation
  • 00:35:25
    which is just basically a slab of
  • 00:35:26
    concrete in the ground that whole thing
  • 00:35:28
    could be filled with a metal
  • 00:35:31
    reinforcement and you can have this
  • 00:35:34
    gigantic
  • 00:35:35
    earth mat under the entire property
  • 00:35:37
    connected through
  • 00:35:39
    problem solved now of course it's all
  • 00:35:42
    very well if you've got a new house so
  • 00:35:43
    you're putting in your driveway
  • 00:35:45
    obviously if you've got an existing
  • 00:35:46
    installation you can't use this because
  • 00:35:48
    it's unlikely the customers wanting to
  • 00:35:50
    pay thousands for a new driveway just to
  • 00:35:52
    have their electric car plugged in but
  • 00:35:54
    certainly at the moment and unless some
  • 00:35:56
    magical solution occurs in the future
  • 00:35:57
    which it
  • 00:35:58
    won't do this is realistically the only
  • 00:36:01
    proper and safe way to ensure that this
  • 00:36:04
    dangerous situation doesn't occur
  • 00:36:06
    the other things in the regulations may
  • 00:36:07
    work in some of the situations such as
  • 00:36:09
    the voltage monitoring or that current
  • 00:36:11
    going to the uh
  • 00:36:12
    through the protective induction to the
  • 00:36:13
    device and then disconnecting it and of
  • 00:36:15
    course there's various combinations of
  • 00:36:16
    monitoring current on various conductors
  • 00:36:18
    and whatever
  • 00:36:18
    but in the end this is really the only
  • 00:36:21
    proper and fully foolproof way of doing
  • 00:36:24
    it
  • 00:36:25
    provided that the electrode resistance
  • 00:36:27
    here is in the single digit ohms that's
  • 00:36:29
    required
  • 00:36:31
    and the final thing we'll just cover
  • 00:36:32
    quickly here is that if you have
  • 00:36:34
    a three-phase supply into your property
  • 00:36:38
    so that would be the three phases or
  • 00:36:40
    three line conductors coming in
  • 00:36:43
    and you've also got the neutral coming
  • 00:36:44
    in as well and of course you would also
  • 00:36:46
    have the
  • 00:36:47
    protective conductor which in most cases
  • 00:36:49
    is going to be part of that anyway
  • 00:36:51
    if you've got that as an installation
  • 00:36:54
    then there is another possible choice
  • 00:36:56
    and this is where this o pen device
  • 00:36:58
    comes from which is made by a company
  • 00:37:00
    called matt
  • 00:37:00
    e because it's got all three phases and
  • 00:37:04
    the neutral
  • 00:37:06
    this and any other devices that might be
  • 00:37:07
    made along those similar lines
  • 00:37:09
    can determine when this conductor has
  • 00:37:11
    been broken
  • 00:37:12
    because what will happen is that the
  • 00:37:14
    voltage point
  • 00:37:16
    if you imagine that was sort of the
  • 00:37:16
    middle point and they were connected to
  • 00:37:18
    it normally that would be
  • 00:37:19
    zero relative to all three
  • 00:37:22
    if that's then broken if you had your
  • 00:37:25
    phase diagram like that
  • 00:37:27
    normally this is at zero in the middle
  • 00:37:30
    when that's broken the neutral point
  • 00:37:31
    goes away because loads on this are
  • 00:37:33
    going to be unbalanced
  • 00:37:34
    that point may shift in one of the three
  • 00:37:37
    directions there so if you said it
  • 00:37:38
    shifted over here
  • 00:37:40
    that's where your dangerous voltage to
  • 00:37:41
    ground occurs but by monitoring the
  • 00:37:43
    current and the voltage across
  • 00:37:44
    all of the conductors that can be
  • 00:37:45
    reliably detected
  • 00:37:47
    and then it can disconnect the whole lot
  • 00:37:49
    so that particular thing is
  • 00:37:51
    totally valid and that is an ideal
  • 00:37:52
    solution but of course it only works
  • 00:37:55
    where you have all three phases
  • 00:37:56
    available in say most domestic
  • 00:37:58
    properties that's not going to be an
  • 00:37:59
    option
  • 00:38:00
    because simply they don't have a
  • 00:38:01
    three-phase supply installed
  • 00:38:04
    so that can be useful let's say only of
  • 00:38:06
    any value with three-phase supply
  • 00:38:08
    if you don't have access to all three
  • 00:38:10
    phases that technology is with no value
  • 00:38:13
    whatsoever and bearing in mind that that
  • 00:38:16
    company that makes that device matter it
  • 00:38:17
    also makes other devices but those are
  • 00:38:19
    again just the voltage monitoring types
  • 00:38:20
    of things
  • 00:38:21
    which we saw earlier which again will
  • 00:38:23
    work in some cases
  • 00:38:25
    unfortunately not all of them
  • 00:38:28
    so that's it for this video and
  • 00:38:30
    unfortunately that's just a big can of
  • 00:38:31
    worms opening up there in terms of what
  • 00:38:33
    you can do with
  • 00:38:34
    electric vehicle charging connections
  • 00:38:35
    but until next time
  • 00:38:37
    thanks for watching
タグ
  • BS7671
  • Electric Vehicles
  • TN-CS
  • TN-S
  • TT System
  • PME Supplies
  • Earthing
  • Safety Regulations
  • Voltage Monitoring
  • Car Charging