[Old Shep]

I am currently charging my Audi Q5 hybrid using the Audi supplied portable control unit. This is from my garage which is a separate TN-C-S 3phase supply, from a separate 32A RCBO through an industrial socket to get the full 7kw - and all is well.
I have an option to supply from the separate house single phase supply (which I'm sure is also TN-C-S), through a pre-installed buried 4mm/2 cable. When testing this arrangement, as soon as I plug in and switch the isolator for the same Audi unit cable (no load), both RCD's on the house split board trip. If it were just the half of the board where its fed from, I might suspect cumulative leakage being taken over the top. But why would both RCD's trip?
Any ideas or similar experience?

 

[Aragorn]

is the neutral wire feeding the "trippy" socket in the correct busbar?

 

[Old Shep]

is the neutral wire feeding the "trippy" socket in the correct busbar?

Cheers. I will check as soon as I get chance. If it’s wrong, could that flip both RCD’s in the board though

 

[Aragorn]

yes, RCD measures the imbalance in live and neutral. If the neutral wire is fed into the wrong bus bar, it will flow its live via one RCD and the neutral via the other, both RCD's therefore detect an imbalance and trip.

Dual RCD boards have a seperate bus bar for each RCD, and the neutrals must return to the correct one.

 

[dk6780]

That would trip with anything using the socket though, not just an unloaded "granny" charger. So does the socket work with other appliances?

 

[HandyAndy]

You said "32A RCBO". My 32A EBSE charged my Ampera at max 14A happily for several years. The very first time I tried to charge Ioniq at 32A, it ran for about 10 minutes then tripped. Reason is these RCDs/RCBOs rated at 32A warm up in use, and once they're above 30C temp, they derate the current gradually as the temperature rises. My Ioniq drew 31.5A. After 10 mins, the small separate metal CU was warming gently, and the temperature got high enough to just drop the max current that tiny bit, and tripped the unit. Solution was to replace anything rated to trip at 32A in the EVSE supply with equivalent item rated 40A. Problem solved.

 

[Old Shep]

That would trip with anything using the socket though, not just an unloaded "granny" charger. So does the socket work with other appliances?

This is actually the first time using that feed from the board since connecting in the new(ish) cable to the garage, so I disconnected again when I encountered this problem. There is a chance that I might be on the wrong neutral bar, so will check it all out again when I get half a chance at the weekend. Also gonna try the control unit with the 13A lead from a house ring main as a process of elimination

 

[Old Shep]

yes, RCD measures the imbalance in live and neutral. If the neutral wire is fed into the wrong bus bar, it will flow its live via one RCD and the neutral via the other, both RCD's therefore detect an imbalance and trip.

Dual RCD boards have a seperate bus bar for each RCD, and the neutrals must return to the correct one.

Just checked out the consumer unit. Yes I had put the new neutral in the wrong neutral busbar. Swapped over and all is good. Rookie error . Thanks for the heads up Aragorn. These forums are great