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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 gkenyon over 5 years ago

SL1:

gkenyon:

The situation that does arise, however, is high inrush current of the rather sizeable transformers. Yes, this can be overcome, but of course costs are now increasing, and we're competing against "forget it, I'll just plug it in to a socket-outlet", which of course is far less practical, and far less safe, but doesn't have the price tag attached.

Hi Mr G Kenyon,

The original idea of my questioning the possibility of using a Double Wound Safety Transformer was to look at an alternative, ( in an industrial and offices based environment), to installing the 'box on the wall with the Type 3 sockets/tethered lead and RCD'- insert manufacturer. Your last line of your quote (above) talks about using the transformer against a socket outlet and cost ( Mode 1). Cost is big driver of bad practises, and I have witnessed at office premises a coiled extension lead plugged into a socket to charge an EV.

My original point was that 722.413.1.2 allows for the supply of one EV from one unearthed source, using a fixed isolating transformer complying with BSEN 61558-2-4.

So Using mode 2 ( BEAMA Guide to electrical vehicle infrastructure), with a dedicated 3 phase circuit (regular charging), a circuit breaker rated for the transformer's in-rush current type D, could be rated at 7.4 KW for industrial use using a BS 60309-02 socket, source: BEAMA Guide, subject to the vehicle protocols.

The secondary side earth cable PE would come from the secondary side of the transformer start point.

The Mode 2 cable providing in cable and protection device (IC-CPD) and downstream RCD protection.

I have asked a transformer manufacturer for costs on this and in an industrial situation, using the safety transformer, and BS 60309-02, and not duplicating an RCD in a dedicated box, could prove cheaper to purchase and install than the units currently being supplied as a standard, and spreading load across three phases would assist energy efficient electrical installations compared to single phase load balancing.

I would appreciate any comments on this idea.

Regards

Simon

Just a thought on this ... Regulation 722.411.4.1 provides other options for three-phase installations. However, I guess such an approach would not be precluded, provided the requisite RCDs are used as indicated in the IET Code of Practice and to meet the requirements of section 722 of BS 7671.
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0 gkenyon over 5 years ago

SL1:

gkenyon:

The situation that does arise, however, is high inrush current of the rather sizeable transformers. Yes, this can be overcome, but of course costs are now increasing, and we're competing against "forget it, I'll just plug it in to a socket-outlet", which of course is far less practical, and far less safe, but doesn't have the price tag attached.

Hi Mr G Kenyon,

The original idea of my questioning the possibility of using a Double Wound Safety Transformer was to look at an alternative, ( in an industrial and offices based environment), to installing the 'box on the wall with the Type 3 sockets/tethered lead and RCD'- insert manufacturer. Your last line of your quote (above) talks about using the transformer against a socket outlet and cost ( Mode 1). Cost is big driver of bad practises, and I have witnessed at office premises a coiled extension lead plugged into a socket to charge an EV.

My original point was that 722.413.1.2 allows for the supply of one EV from one unearthed source, using a fixed isolating transformer complying with BSEN 61558-2-4.

So Using mode 2 ( BEAMA Guide to electrical vehicle infrastructure), with a dedicated 3 phase circuit (regular charging), a circuit breaker rated for the transformer's in-rush current type D, could be rated at 7.4 KW for industrial use using a BS 60309-02 socket, source: BEAMA Guide, subject to the vehicle protocols.

The secondary side earth cable PE would come from the secondary side of the transformer start point.

The Mode 2 cable providing in cable and protection device (IC-CPD) and downstream RCD protection.

I have asked a transformer manufacturer for costs on this and in an industrial situation, using the safety transformer, and BS 60309-02, and not duplicating an RCD in a dedicated box, could prove cheaper to purchase and install than the units currently being supplied as a standard, and spreading load across three phases would assist energy efficient electrical installations compared to single phase load balancing.

I would appreciate any comments on this idea.

Regards

Simon

Just a thought on this ... Regulation 722.411.4.1 provides other options for three-phase installations. However, I guess such an approach would not be precluded, provided the requisite RCDs are used as indicated in the IET Code of Practice and to meet the requirements of section 722 of BS 7671.
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Double wound safety transformer for EV supply.

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