Electric Vehicle charger installation

[Tronco]

How would you suggest connecting 2 EV chargers to a consumer box?
Both 32A; on the same line, 64A total, or 2 seperate feeds.
Also, is this really practical for a single household considering average power consumed by the household? i.e. if both chargers were on simultaneously at a peak consumption time.

 

[ericmark]

Because unlikely you can get a 64A MCB I would say no option but separate feeds although it could be the same 4 core cable.

I would say 64A is to a point where at least a phone call to DNO would be required. On a house where I thought the 100A single phase may have not been enough I used a 160A switched fuse with 100A fuses fitted to supply separate consumer units so if required the supply could be over 100A or split into phases. With this in mind using a separate consumer unit for chargers may be best move.

To me the big problem is the TT requirement and the proximity of earthed extraneous-conductive-parts where they may be within hands length and using different earth system. The same situation where of course a caravan is charged at home the regulations say TT supply but does this mean turning whole house to TT rather than TN-C-S.

I will watch with interest the replies as this is likely to happen more and more now.

 

[Spark123]

TN-S is fine too.
I'd suggest getting an electrician in to do it for you as it isn't really DIY and requires notification to your local authority building control.

 

[Iggifer]

regardless of whether or not you can get a 64a MCB (I'm sure a 63a one would suffice perfectly well)

I would want these on two 32a MCB's regardless,

 

[Spark123]

I don't think domestic consumer units are suitable for use with MCBs over 50A, you'd have to check the manufacturers specs. Don't be misled by the fact you can buy them - some are intended for the industrial range of CUs.

 

[ericmark]

TN-S is fine too.
I'd suggest getting an electrician in to do it for you as it isn't really DIY and requires notification to your local authority building control.

Looking at page 3 first column If an EV cannot be charged inside the building, then the building's PME earth should not be used; So yes TN-S is fine but TN-C-S is not. How one can be certain the supply is TN-S and will never be changed to TN-C-S I don't know. One would need a letter from the DNO saying it was TN-S as the combining may be further back to where one can see.

 

[ban-all-sheds]

What's the difference between "If an EV cannot be charged inside the building, then the building's PME earth should not be used" and "No external sockets should be installed with PME supplies"?

Because I don't think I've ever seen the latter stated.

 

[securespark]

An EV supply should be TT'd and a type A RCD installed, but reference should be made to the manufacturers installation instructions, as some equipment is not suited to Type A's and could cause premature failure of the RCD.

 

[JohnW2]

What's the difference between "If an EV cannot be charged inside the building, then the building's PME earth should not be used" and "No external sockets should be installed with PME supplies"? Because I don't think I've ever seen the latter stated.

Oh dear - did you perhaps think it was time for another long thread? ... and have you not read the writings of Bernard?

Kind Regards, John

 

[bernardgreen]

Oh dear - did you perhaps think it was time for another long thread? ... and have you not read the writings of Bernard?

which are based on experience of "earths" not being the same potential as the ground.

In my opinion "earths" that are not connected to the local ground should not be exported outside the equipotential zone created by the "earthed" CPC in the installation.

There would be a strong reaction to anyone suggesting it was safe to touch the neutral wire yet that is, in electrical terms, exactly what one is doing when touching an item "earthed" by a CPC in a PME system.

Note 99.9% of the time the neutral derived "earth" is safe and effective.

 

[ericmark]

What's the difference between "If an EV cannot be charged inside the building, then the building's PME earth should not be used" and "No external sockets should be installed with PME supplies"?

Because I don't think I've ever seen the latter stated.

I had to read a few times before it registered but yes there is a problem in that we have to provide an earth connection even when it is to supply a class II item.

Outside sockets are in the main used for Class II stuff but the question has be asked before what if the home owner wants to plug in his motor home or caravan to maintain the batteries over long time storage?

The point was raised that although a caravan or motor home it is not a caravan site and as such section 708 does not apply. Also often they are parked closer to the house than fire regulations would allow on a caravan site so there could be a connection between extraneous-conductive-parts like cast iron drain pipes and the vehicle at the same time.

Where houses are close or even joined again one can have extraneous-conductive-parts of one house touchable at the same time as an extraneous-conductive-part of a neighbours house which is why the DNO select the earthing system not the electrician or home owner.

For the electrician to do a risk assessment and use his expertise to decide if to export house earth or to use TT is fair enough, but to recommend that TN-C-S is never exported will with some properties it may not be appropriate.

The IET paper on supplies to vehicles is to me trying to create a standard where really it should be left to the electrician to select. However it makes it hard not to TT a charger point with a TN-C-S supply as 10 years or less down the line when the next EICR is done your work may be rejected as non compliant.

Although the song may say we all live in little boxes and we all turn out the same in real terms this is not the case. My house has plastic external pipework and all external electric devices are above hands reach but my mother has metal pipe work which is a problem with a narrow drive way between the houses were one would naturally park a car and not to use the TN-C-S would present a danger.

To my mind there are just too many rules. Common sense should prevail but while the rules are there we have no real option but follow them.

 

[JohnW2]

Oh dear - did you perhaps think it was time for another long thread? ... and have you not read the writings of Bernard?

which are based on experience of "earths" not being the same potential as the ground. In my opinion "earths" that are not connected to the local ground should not be exported outside the equipotential zone created by the "earthed" CPC in the installation.

Indeed - and, as you know, I don't (can't) disagree with the theory of what you are saying. As we've discussed, it even extends to an undesirability of having outside plumbing (e.g. outside taps) which are in electrical continuity with pipework bonded to a TN-C-S earth, or to export of a TN-C-S earth to an outbuilding which, although it doesn't have any extraneous-c-ps, has, say, a metal lightswitch by the door which can be touched by someone outside of the outbuilding. However, that's all theory - I think that the thinking of many people is related to (probably with a few more 9s):

Note 99.9% of the time the neutral derived "earth" is safe and effective.

However, we don't need to discuss all that yet again ... In terms of the matter we are discusing, I don't know what the (electrical) situation is with these EV chargers - significant theoretical concern would presumably only arise if they are such that the car bodywork (a large body of conductor) is connected to the supply earth, and I don't know if that is the case.

[as an aside, I would suggest that even more potentially dangerous than an exported TN-C-S earth is a TT earth exported from an installation which does not have full RCD protection]

Kind Regards, John

 

[JohnW2]

Where houses are close or even joined again one can have extraneous-conductive-parts of one house touchable at the same time as an extraneous-conductive-part of a neighbours house which is why the DNO select the earthing system not the electrician or home owner.

I don't think that's necessarily true. Whilst a DNO may provide/'offer' a TN earth, I don't think there is any compulsion to to use it - AFAIAA the electrician or home owner can decide to ignore it and use TT if (s)he so wishes. Of course, if the DNO does not supply a TN earth (and I don't think they are obliged to, if they never have provided one), then there obviously is no choice for the electrician/householder.

To my mind there are just too many rules. Common sense should prevail but while the rules are there we
have no real option but follow them.

Quite so - and in countless walks of life.

Kind Regards, John

 

[stillp]

concern would presumably only arise if they are such that the car bodywork (a large body of conductor) is connected to the supply earth, and I don't know if that is the case.

I believe that is usually the case.

A further complication is that the charging circuit of the EV usually contains EMC filters connected to 'earth', so there is significant current in the protective conductor, and any interruption of that protective conductor's connetion to earth will result in it immediately rising to supply potential.

 

[JohnW2]

concern would presumably only arise if they are such that the car bodywork (a large body of conductor) is connected to the supply earth, and I don't know if that is the case.

I believe that is usually the case.

If that's the case, then there clearly is a potential (excuse pun!) issue - just as there would be if one connected a TN-C-S earth to any large metal object (insulated from earth) outdoors.

A further complication is that the charging circuit of the EV usually contains EMC filters connected to 'earth', so there is significant current in the protective conductor, and any interruption of that protective conductor's connetion to earth will result in it immediately rising to supply potential.

That makes sense, although I'm not sure that such an "interruption of the protective conductor's connection to earth" is necessarily appreciably more likely with TN-C-S than with any other earthing system, is it? As a side issue, what sort of charging voltage are we talking about?

Kind Regards, John