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Electric vehicle charger cable

Discussion in 'Electrics UK' started by whistler, 1 Sep 2021.

  1. whistler

    whistler

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    A few years ago I had a plug in hybrid vehicle which only charged at 16 amp, 3.5kw. So I had a charge point installed cabled to its own mcb in the consumer unit. The installation was rated for 16amps.

    Time has moved on and my latest EV will charge up to 32 amps 7kw. I am proposing to have the charge point replaced but I'm wondering if the cable from the charge point to the consumer unit is rated 16 or 32 amps. Is there any way of identifying the cable type?

    Getting a electrician in to replace the charge point would be fairly easy, but if the cable needs uprating, it would be a bit messy as it currently runs through a ceiling void.

    I can't see any identifying marks on the cable. Is there any way of identifying it?

    I guess an experienced electrician would just look at it and say is Xamps. But I would like to know in advance.
     
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  3. AndyPRK

    AndyPRK

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    Usually has 6mm written in the outside

    is it round black cable ?
     
  4. whistler

    whistler

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    Its round white cable.

    If its 6mm is that 32 amps?
     
  5. AndyPRK

    AndyPRK

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    Yes.
     
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  6. davelx

    davelx

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    Though check the voltage drop over the distance. I wired my 7.5kW unit in 10mm² to the isolator switch and then 6mm² to the charger, on a 40A MCB (not good to run a 32A MCB at 32A for long periods). Over rated, but the cables (clipped direct/resting on the slab) still get quite warm.

    (Charger has built-in type A RCD and 6mA DC protection, TN-S earthing).
     
  7. ericmark

    ericmark

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    This is the major problem today, your lucky with a TN-S supply, but with auto disconnection systems, for TN-C-S some using earth probes, some using voltage which must be in the 207 to 253 volt range, and some converting to TT, it is very hard to give advice, as so easy unless on site, to miss something.

    Electricians have to go for special training to fit EV charging points, and no wonder, personally I think TN-C-S should be banned, it is too likely mistakes are made with it. Especially where also gas is also used, there have been some nasty fires, often as with most accidents three faults not one, bonding put before insulating block on gas, use of TN-C-S, but not PME i.e. no multiple earths, and some one has stolen copper, always blamed on the latter.

    With motor vehicles parked outside, one has to accept animals may touch it, so the body of the car needs to be at ground potential, be it cat, dog or postman, animals can touch the car, one would expect the body to be insulated from the supply earth, like most items used in the garden, lawn mower, hedge cutter etc, maybe they are? However it seems there is no rule saying they must be class II, so we can't connect the car to a TN-C-S earth unless it can auto disconnect from the earth in the event of a supply fault. Or connect at TT.

    I know at work the 22 kW charge points are TT. But not so simple at home, we have special charge point like the Zappi designed to get around the problem, and other like the Tesla which expect the precautions to be done else where. So there is no one system fits all, and the answer is get some one who is trained on how to fit the charge points to advise, it is not really some thing to be worked out using a forum.
     
  8. davelx

    davelx

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    Yes, well, as a Electrical Engineer I don't find this particularly complicated!

    The starting point is not to say "well, it could be this, or that,or the other", but to look at what it actually IS in the case in question and work from there.
     
  9. ericmark

    ericmark

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    So what IS it? To me, also as an Electrical Engineer, the problem is any EV supply needs to be safe with any vehicle which can be plugged in, it may be safe with an ABC but not with an XYZ and the installer needs to be sure safe with whatever can be plugged in.

    The EV points worry me, I love seeing the fox, badger, and other wild life, and having had a mother wheel chair bound I realise the problems with cars parked on walkways, at the moment not that many EV's, but I see the problem with knee jerk reaction, we have seen it with the diesel car, not so long ago it was seen as the best way forward, then as we started converting we realised not quite as good as we first thought. I feel the EV is another knee jerk reaction, and as they become more popular we will realise not quite so green as we first thought.
     
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  11. SimonH2

    SimonH2

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    Well, one place to start would be identifying the cable and work from there. If you are (safely) able to show one end where the sheath is stripped back and the cores exposed then that could be a bonus. But any photos need scale so there's a chance of someone being able to say "that's xxx cable, and that diameter would be xxx mm²".
    Without any clues as to the type and size of cable, it will remain a "how long is a piece of string ?" question.
     
  12. whistler

    whistler

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    Sorry for the delay in replying.

    I couldn't see any markings on the cable, but a bit of googling came up with cable outside diameters. I measured this at 9.7 mm, which suggests its 25amp cable, which I guess makes sense for a 16 amp Installation.

    So it looks like a new cable if I decide to have the charge point upgraded.
     
  13. SimonH2

    SimonH2

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    Being pedantic, there is no such thing as "25A cable". A single cable type & size will have a number of different current carrying capacities depending on type of load, ambient temperature, installation method (closely linked to ambient temperature), what the ends are terminated into, how it's protected against overload and fault, ... Furthermore, just an outside diameter isn't enough to identify a cable - e.g. a wire armoured cable will be considerably larger in overall diameter than the same size of non-armoured cable, and the type of insulation affects the current carrying capacity.
     
  14. whistler

    whistler

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    So how would you identify the cable to determine whether it is suitable for a 32 amp load? Just to clarify, its a white round three core flexible cable, no visible markings, no armoured and measuring 9.7mm diameter. It was Installed for a 16 amp load. That's all the info I have.
     
  15. EFLImpudence

    EFLImpudence

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  16. whistler

    whistler

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    Thanks. That confirms it 9.7mm diameter, 25a rating, so I will need the cable upgrading
     
  17. SimonH2

    SimonH2

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    Well the first step is to work out what sort of cable it is ... things like :
    You didn't tell us that up above - in fact you didn't tell us anything other than that the cable was installed for the current charge point. And that's why you got asked for more information on the cable. Based on what you've now told us, it is most likely 2.5mm² PVC flexible - and as that would be the lowest current carrying capacity of the alternatives then it would be reasonably safe to assume that.
    BTW - it would be unusual (but not unknown) for there to be no markings, but they are often very hard to see. I have some cable here that's printed in pale yellow on a white cable, and it just looks like a "dirty smudge" until you look at it closely - or just disappears once the cable ages a bit and gets dirty. Mostly they are embossed in the sheath, but sometimes so shallow that you need to get a light at just the right angle to read them.


    Consulting Appendix 4, table 4D2A of BS7671 (a.k.a The Wiring regs), the current carrying capacity of a 2.5mm² multicore PVC cable, single phase, ranges from 18.5A (Reference Method A (enclosed in conduit in thermally insulating wall etc.)) to 30A (Reference Method E (in free air or on a perforated cable tray etc, horizontal or vertical)). As it's a flexible cable, these need to be adjusted by a factor 0.95 (app 4, section 2.4), so that makes a range from 17.6A to 28.5A.
    That's why there is no such thing as "a 25A cable". The cable that EFL has linked to, and has "25A" given as it's current rating, could actually be rated as low as 12.74A if protected by a rewireable fuse box (apply a further 0.725 adjustment factor) and possibly lower if subject to high ambient temperatures, or as much as 28.5A. So just assuming "it's good for 25A" could mean it being almost 50% under-sized in some applications.


    But back to your original question ...
    Does you new vehicle "have to" charge at 7kW, or can it charge at 3.5kW ? Do you "need" it to charge at 7kW ?
    If the vehicle can charge at 3.5kW, and you don't need it to charge faster, then why not just stick with what you've already got ?
     
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