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leebut

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hiya chaps


I did a City and Guilds course, practical assessment and exam for the CG2919 on Monday and Tuesday, we were told about the difficulties with ensuring the safety of the charging equipment especially regarding the earthing in domestic properties, lots of discussions were about using the isolating transformer instead of converting the existing property to a TT system.


My question is which isolating transformers do you EV guys use typically looking at supplying a 7 Kw charging unit, where do you get them from and what is the cost of them.


Regards


Lee
 
Bill01803


The issue isn’t conversion of the clients property to a TT system, if there is any class 1 light outside fittings or bonded pipes to gas or water within 10 metres of the charging point you have the risk of dangerous touch voltages under earth fault (possibly from neighbours property etc) it’s part of the risk assessment you have to carry out prior to installation.

EV installation not straight forward external influences play a big part of installation, if you change the property from a PME to TT there’s always a risk of another electrician who doesn’t know the legislation on EV installation puts the PME connection back.

Also some ground conditions you would struggle to get the earth potential acceptable for the EV installation, hence why in the installation it’s easier and straight forward to install an isolating transformer.


Lee
 
I can understand not wanting to get involved with checking and changing electrical instalations and then being responsible for that instalation to some degree. but it;s not that easy with a 7kw load involved, that's not exactly a trivial load, and any transformer of 7kw capacity will be large and expensive, so there is NO easy way out. I say forget the trasformer idea ! it's just not practicle.
 
OP, could you clarify - were you meaning make the whole house electrical system TT?
 
I can understand not wanting to get involved with checking and changing electrical instalations and then being responsible for that instalation to some degree. but it;s not that easy with a 7kw load involved, that's not exactly a trivial load, and any transformer of 7kw capacity will be large and expensive, so there is NO easy way out. I say forget the trasformer idea ! it's just not practicle.



Check out the wiring regulations on EV charging it’s the only sensible way to go with PME unless the DNO can guarantee that there will never be a damaged cable to the neutral you need to carry out a risk assessment on the installation, I did my City and Guilds 2919-10 on Monday and Tuesday this week and going through the regs the only solution is to go down the isolating transformer (been told there’s a small unit that does 7Kw that fits a din rail unit ( not in a CU) that’s around the £200 +Vat price range just trying to find who sells it)
 
Sorry they’re not in order

If there’s a class 1 light or bonded pipe within 10 metres of the charging point the charging point cannot be on a separate earthing system to the property or the neighbours property
 
I've never installed a charging point and unfamiliar with accepted practice, but I can say with certainty that no 7kVA wirewound transformer ever mounted on a DIN rail. It will be in the order of 50-60kg and the size of a case of wine unenclosed. This is due to physical limitations of the copper and steel, and until someone invents a revolutionary material with better properties, it won't change much. It is possible to make a smaller, lighter switched mode converter, although not for a few hundred pounds.

But, surely the sensible approach is a device that disconnects the supply in the event of the PME earth exceeeding 70V to local mass of earth, as detailed in 722.411.4.1 option (iii). Put in two small spikes nearby (resistance need not be very low, and the two would allow for automatic monitoring of resistance), see the green light come on and the job is done. It's basically an improved version of a VOELCB used for a more suitable purpose, obviously with a bit of engineering to make it reliable enough to switch the PE as well as the live conductors.

I have to wonder why the charging point makers don't offer an integral solution. 722.411.4.1 option (iii) even suggests the voltage detection device could be included in the charging equipment. The convenience of being able to install one product to any supply without further complications would surely be attractive in spite of increased cost.
 
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Can't see how its possible to fit an EV charger in most cases then. Back to petrol we go!

Sorry LeeBut a 7kw isolating transformer will be around £1000 and pretty large. Not an option.

Is your book saying a EV charger electrode can't be within 10m of a buried metallic bonded pipe, outside light, outside socket etc etc. Doesn't sound like this is possible in most cases where the charger would be mounted to an outside wall of a dwelling.

Anyone else that's done the course? Thinking of doing it soon, but if this is the case!
 
Can't see how its possible to fit an EV charger in most cases then. Back to petrol we go!

Sorry LeeBut a 7kw isolating transformer will be around £1000 and pretty large. Not an option.

Is your book saying a EV charger electrode can't be within 10m of a buried metallic bonded pipe, outside light, outside socket etc etc. Doesn't sound like this is possible in most cases where the charger would be mounted to an outside wall of a dwelling.

Anyone else that's done the course? Thinking of doing it soon, but if this is the case!



Yes it does, this is the reason why they say you should go down the isolating transformer route because if you live in a new estate house close together you cannot guarantee safe earthing if you convert property to TT. system
 

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