This might have been chewed around a bit.
So from a BS7671 point of view there’s a number of risk assessment issues surrounding EV chargers and the Earthing system for the installation and it’s proximity to other types of earthing system. So let’s just say you’re the luckiest sparkie ever, you’re installing an EVC on a farm miles from anything, the earth rod has a surprisingly low resistance to earth and off you go.
so my question arises from the need to protect all final circuits with a 30mA RCD on a TT installation. Now I’ve got no problem with the additional cost of installing a little dedicated unit to supply just the charger incorporating a 30mA RCD of the B variety, however the problem arises with selectivity as I am yet to find an EVC designed for the domestic sector that doesn’t include its own 30mA RCD as part of the charger. Contacting a popular manufacturer I asked if the RCD could be removed from the charger and installed upstream, the short answer “no”, the long answer “goodbye warranty”. Obviously with this in mind I might be pushed towards a 100mA Stype up front but this still posses a problem in many installations especially with a TT system where a 30mA RCD is realistically going to be required upfront in the consumer. With a PME installation I’d be inclined to have a 60898 MCB upfront, perhaps using SWA to protect the cable where necessary but that’s not going to be ideal for TT and neither is having two 30mA RCDs one upstream and one down stream. Even with TN installations there are going to be clients who insist on having the cable hidden within their paper thin walls, which again pushes me towards protecting that cable with a 30mA RCD.
So, what’s everyone’s thoughts, is it acceptable to ignore selectivity between RCDs where reasonably it’s possible to reset both if necessary, is 30mA RCD protection more important than selectivity ? Is there a technology solution, do the manufacturers need to catch up? Have I been corrupted by years of RCD dogma as a house basher and am missing an obvious trick? How do you approach a car charger on a TT system?
I don’t mind TT installations myself, I’ve taken to installing RCBO boards and suitably protecting the incoming supply tails by way of double insulation and a compression tails entry gland designed for that exact purpose, my preferred brand of board also has optional tails clamps that go in above/behind the main switch for additional protection from movement. But still I’m faced with a selectivity problem.
Thanks in advance for your thoughts.
