There doesn't seem to be much point in a 30mA RCD if the socket outlet is DC (mode 4) - it's not going to provide additional protection (e.g. in the case of a damaged flex) like it would for a directly connected AC system (modes 1-3).

I suspect NOTE 2 to 722.531.3.101 is the giveaway - it's still "under consideration"....

  - Andy.

Hi Andy, thanks for your response.

I hear what you say about Note 2 of 722.531.3.101. I also understand that the RCD won't be providing additional protection on the DC side.

However, If you look to Appendix J of the EV charging CoP (5th edition), you'll notice that it calls for electrical separation to be established using an isolating transformer to BS EN 61558-2-4. EV charging manufacturers are stating that galvanic isolation is provided but not by means of an isolating transformer to BS EN 61558-2-4.

Furthermore, If you look to section J2 of Appendix J, you'll see the following: BS 7671 does not, at present, require RCD protection for the DC output to the vehicle. An appropriate RCD should, however, be provided on the AC input to DC charging equipment without separation, according to Regulation 722.531.3.101.

Am I missing something?

It is the charging point that requires additional protection by 30 mA RCD, not charging equipment.

RCD protection of DC outlets is not really supported by "AC RCDs" (of the types specified in BS 7671).

Bh said:

An appropriate RCD should, however, be provided on the AC input to DC charging equipment without separation, according to Regulation 722.531.3.101.

This is good practice, but I understand that "leakage currents" may, in some cases, make 30 mA RCD protection impractical.

HOWEVER, I think the thing that is being "missed" is that 722.531.3.101 also contains requirements for selection of RCD Type. Where RCDs are required for ADS (e.g. TT system on AC side, or where disconnection times can't be met by OCPDs), the TYPE of the RCD is selected according to 722.531.3.101 where separation is not achieved - you will, effectively, need a Type B because of the possibility of DC leakage currents

However, If you look to Appendix J of the EV charging CoP (5th edition), you'll notice that it calls for electrical separation to be established using an isolating transformer to BS EN 61558-2-4. EV charging manufacturers are stating that galvanic isolation is provided but not by means of an isolating transformer to BS EN 61558-2-4.

I guess your other option is to provide an isolating transformer upstream of the EVSE, so that the EVSE and its immediate supply circuit are protected by separation.

   - Andy.

Graham,

first and foremost, thanks for the reply. It's quite amazing to think someone can post a question on this forum and speak directly with the lead author of the EV charging CoP. It goes to show how good of a resource this forum is! Straight from the horse's mouth...

I'd agree that there is a real need (in most cases) for a type B RCDs because of the possibility of DC leakage currents, the last thing we want is the RCD to be blinded. I also think it's important to consider the issues associated with having type B RCDs downstream of type A RCDs, I've seen it overlooked a number of times.

gkenyon said:

Bh said:

An appropriate RCD should, however, be provided on the AC input to DC charging equipment without separation, according to Regulation 722.531.3.101.

This is good practice, but I understand that "leakage currents" may, in some cases, make 30 mA RCD protection impractical.

Could you please explain why it's considered good practise? After all, you did say the following:

gkenyon said:

RCD protection of DC outlets is not really supported by "AC RCDs" (of the types specified in BS 7671).

thanks, Bh.

Bh said:

Could you please explain why it's considered good practise?

Whilst the words are agreed by Committee, I can give a personal opinion here being that in converters without separation, you're effectively connecting mains through a controlled rectifier and a bit of electronics. If the electronics break down somehow, it's theoretically possible you're connected to the AC mains.

Leakage is an issue, so a 30 mA RCD on the AC side might not be possible ... so if you have a TN system on the AC side, it's really this is a question to the manufacturer as to whether an RCD is necessary on the AC side, and what rating  and type should it be?

Sorry to tail onto an old thread, but one of the example isolated mode 4 charger systems has PFC on the front end (IEC 61851-23). As this is all prior to isolation I guess Type B would be required in this case?