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Double wound safety transformer for EV supply.

Hi everyone, I have only posted once before so thanks to anyone who replies!

I am following on from the earlier "70 volt PEN conductor not allowed to exceed post", and looking into supplying a client with an electric vehicle power supply from a three phase isolating transformer BS 7671 722.413 (1.2): " The circuit shall be supplied through a fixed isolating transformer.."

The general consensus seems to be that an external IP box with an RCD (Type B) and a tethered lead is the standard to follow, and this may be the only option with a 230 volt domestic supply, but why not use a 3 phase 400 volt step down or tapped, safety double wound isolation transformer in a standard 100 -200 ampere or above industrial units/sheds?

( Subject to load and diversity).

The answer often stated when I have asked sparks/engineers is that in-rush current are too high but a type D CB BS 60898 will 'let through' the in-rush ( the transformer manufacturer agrees), and will still give at 5 seconds- (final circuit exceeding 32 A) 0.44 ohm EL ( 10oC) , so is achievable in many situations local to Birmingham.

I was then going to run a fused cable out to an external isolated IP 65 box with a Type 2 socket to IP44 or above ( 722.55.101).

Isn't it better to engineer a solution to the upcoming electric charger deluge, rather than buying (insert well known manufacturer name here), and lots of single phase loads usually dumped onto L1?

I would be interested in any thoughts or problems you may consider....

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0 SL1 over 5 years ago

Thanks for the reply Mike.

Very interesting to note your comments on connecting on side one side of the secondary to earth via an electrode. Would this make the secondary side no longer isolated though? Could stray voltages from the PEN network come back up the electrode and CPC spoil the double insulated advantages?

Earthing the core is sound advice.

Your comments on staggered start are interesting because our clients is talking about numerous chargers being installed, possibly all coming on-line when people return late afternoon with their cars. Spreading and managing loads with electric vehicles surely will be a major issue coming down the line. I will have a look at 'negative temperature slop inrush limiters', and also the contactors and ( bosky) resistor for the slow start components. Your point about' catching' the resistor if there is a timing issue is a good one!?.

Thanks Simon
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0 SL1 over 5 years ago

Thanks for the reply Mike.

Very interesting to note your comments on connecting on side one side of the secondary to earth via an electrode. Would this make the secondary side no longer isolated though? Could stray voltages from the PEN network come back up the electrode and CPC spoil the double insulated advantages?

Earthing the core is sound advice.

Your comments on staggered start are interesting because our clients is talking about numerous chargers being installed, possibly all coming on-line when people return late afternoon with their cars. Spreading and managing loads with electric vehicles surely will be a major issue coming down the line. I will have a look at 'negative temperature slop inrush limiters', and also the contactors and ( bosky) resistor for the slow start components. Your point about' catching' the resistor if there is a timing issue is a good one!?.

Thanks Simon
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Double wound safety transformer for EV supply.

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