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13A EV socket

lyledunn
TNCS system in local development. Second hand BMW 330E Hybrid with ICCB that appears to restrict charging to 6A. Owner wants 13A socket on outside wall of house. 

The area is near the Mourne mountains where an Ra of 200 ohms would be difficult to achieve with a single rod. In any event the driveway has just be nicely finished. It would be a simple matter of drilling through the back of the meter cupboard to provide  the 13A socket but it is the loss of neutral protection that is the problem. Anyone know if loss of neutral protection is available as a separate item?
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    That is an interesting idea - in effect you are suggesting monitoring electrode current at the substation. I am not sure about this, as part of normal operation will involve quite a bit of electrode current even when there is no fault, as the earth path is in parallel with the neutral, depending a bit on phase balance, and things like how local water pipes are arranged. However I take the point that in fault the electrode current at substation, and at other places as well  will rise relative to the normal case and a  sudden step could be reported as needing investigation, if not an immediate trip. It would require telemetry from substation back to some central HQ, I'm not sure if projects to add telemetry (e.g, https://www.ashwireless.com/pages/35-substation-temperature-monitor)

    could easily be augmented to phone home with additional parameters. You may need to find a way of putting current transformers around the mounting bolts of some large lumps of steel as well, not all transformers are on wooden poles with an easily identifed LV earth wire coming down the side.

    You could extend the idea and telemeter the current flowing into the bonding conductors at preemies with a smart meter..

    I fear there is no appetite for such cunning however, the idea is to keep the existing running as long as possible.
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    "With a PME LV network you cannot tell fault current to earth from neutral current,"

    This is generally true but surely, at the PEN to earth connection at the substation you can. If there is a PEN break, then the entire load current of the properties beyond the break must return via earth, the exact amount depending on how good the earth is at the property. Some of this will find its way back into the PEN conductor at other properties but much of it will travel through earth until it arrives at the transformer earth.

    It should not be beyond a protection engineer to set the level at above the allowable general leakage and below that which would detect a PEN break.
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    Harry Macdonald:

    I can't help thinking that the onus for detecting and making safe an installation following a PEN break should rest on the DNO not on every household that is being supplied. Especially with the advent of EV charging. 

    It should be quite easy to detect a break at the source substation simply by measuring the current in the neutral earth link

    Or am I being too simple here.

    Definitely oversimplification ... diverted neutral currents can happen in any case, especially where there are large amounts of interconnected extraneous-conductive-parts.


    HOWEVER, interesting that, as I understand it, the main distribution companies in Australia are being mandated to put in place voltage monitoring using the Smart Meter system they are installing.


    Should be possible here in the UK ... I'm sure GDPR can be overcome in the way it seems to have beem for the purposes of combatting extraction ...
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    I suppose I will have to clear my garage out if I buy an EV to charge it indoors.
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    If it is a PME supply with TNCS installation then you should use a double pole socket. Don't know if you can get an outdoor weather proof one but there are plenty of indoor makes around , looking at ones yesterday in Homebase. Scowling a bit about all these new silver switch bar ones , excellent looking of course for switches four bars in a row  for a multi gang switch. No the centre pivited long bar on sockets only takes the slighted touch to flick it over' a dog / cat small baby could switch on. Around here with PME/TNCS the main earth goes from the cut-out neutral to the metal consumer earth bar which is bolted to the metal casing , the earths now separate from the neutral in the installation, but do they? no still connected to neutral , (and the regs still call the neutral a live conductor). 

    I have seen the result of a aluminum armour  installed around a large factory fence  for security lighting , a cold poured plastic T joint was made at each lighting pole with copper SWA cables to the pole lights, about 6months later what a mess having to break open the joints , copper to aluminum corrision don't  mix.  With old supply  copper overheads between houses now being changed to aluminum ABC's but with the existing copper service drop from the power company's aerial power lines still being used , I predict some trouble in years to come and neutral faults.

    Below is the inners of a double pole switch socket.


    Double Socket, Double Failure, Double Pole - YouTubewww.youtube.com › watch › v=gkNSzAeStws


    regards

    jcm
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    If you had a TN-S system back to the substation, you could look at the balance of phase and neutral currents and detect faults down stream in an RCD (or earth fault relay) style.

    In this strange parallel universe, you'd want each house to be equipped with an RCD at the incomer to remove any from the network that would lead to tripping of the LV network RCD.


    With a PME LV network you cannot tell fault current to earth from neutral current, so such protection is impossible. Oddly this was first brought home to me in the generator yard at Agrekko near Milton Keynes, when the chap showing us what they had, explained to us all that a special key switch for earth fault detection disable, was fitted to all the gensets they may be called upon to provide to the local DNO, so they could feed in at a faulty substation, in to a network with in effect the biggest NE short going.

  • 0
    I can't help thinking that the onus for detecting and making safe an installation following a PEN break should rest on the DNO not on every household that is being supplied. Especially with the advent of EV charging. 

    It should be quite easy to detect a break at the source substation simply by measuring the current in the neutral earth link

    Or am I being too simple here.
  • 0
    mapj1:

    If the advice only covers the case of the broken PEN just outside your own property it is missing a whole slew of more likely fault cases (there being probably one PEN joint that can fail to isolate only one property, and a multitude of joints that can fail in  way that isolates more than one.).

    I agree any attempt to use electrodes to hold the neutral down close to ground potential on both sides of a break in a current carrying circuit is pretty much futile.

    Hence bosky bonds to plumbing and advice to TT to the local surface potential if it really matters.



     


    Agreed on the "only covering PEN outside your property". However, if we're talking about a dwelling, using the full maximum demand perhaps errs on the side of caution by a good way. In addition, in a three-phase installation, the electrode resistance depends not only on the demand downstream of the PEN break, but also on the phase imbalance ...


    With respect to "TT the local surface potential", the local surface potential drops off quite rapidly, perhaps even the difference between one side of a parked vehicle and the other ... forget about it's length ... and you've no idea where buried metalwork connected to PME is located ...


    Shock risk is reduced if you're on certain surfaces (e.g. paved/tarmac) but not dependable (weather, ground saturation conditions, etc.)


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    We appear to be back to what if high cpc-pme-neutral currents running in live conductors suddenly need a cpc.

    It may be an idea if we reconsider the use of a separate earthing system using exsisting/new/adapted utility services.

    An example maybe that while companies such as Gigaclear/fix/stuffed continue to rollout fast fibre they might install the earthing alongside.

    Don't worry chaps i'll eventually get my coat.

    Legh
  • 0
    If the advice only covers the case of the broken PEN just outside your own property it is missing a whole slew of more likely fault cases (there being probably one PEN joint that can fail to isolate only one property, and a multitude of joints that can fail in  way that isolates more than one.).

    I agree any attempt to use electrodes to hold the neutral down close to ground potential on both sides of a break in a current carrying circuit is pretty much futile.

    Hence bosky bonds to plumbing and advice to TT to the local surface potential if it really matters.



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