RCD protection required for SWA outside?

[rebuke]

I haven't got a copy of the regs handy, so I was wondering if someone could do me a favour and tell me if I need to have RCD protection on a piece of SWA running outside?

It will be linking my main house consumer unit to one in a brick outbuilding, which will have a 30mA RCD main switch or perhaps RCBOs for each circuit, so the final circuits (lighting in outbuilding and some socket outlets) will all be protected.

My original plan was just to put the entire supply on a 30mA RCBO in the house consumer unit, however my LABC have come back saying that I need to use 100mA RCD/RCBO in the house, and then put a 30mA RCD/RCBOs in the outbuilding to take into consideration discrimination.

The problem I have is the brand of consumer unit in the house doesn't have 100mA RCDs/RCBOs available, so it would probably mean fitting a separate unit, which might be tricky as there is limited wall space available. If however I am not required to protect the SWA, then I can just put that on an MCB, and put the RCD protection in the outbuilding consumer unit, which would solve all the problems...

 

[holmslaw]

..

 

[Taylortwocities]

I need to use 100mA RCD/RCBO in the house, and then put a 30mA RCD/RCBOs in the outbuilding

But that will not give you discrimination of RCDs. Just think, which RCD would trip first if you had an earth fault of, say, 150mA.

The 30mA?
the 100mA?

it will be the RCD that has the faster trip time. Could be either, could be both. To provide discrimination you would use a 100mA time delayed RCD upstream with a 30mA downstream.

but per the above, you do not need one upstream on the SWA.

What type of supply do you have by the way? TT, perhaps?

PS
Hope you find where you left your regs book.

 

[rebuke]

Supply is TN-S - I didn't quite understand why they'd come back saying that, as I agree, it doesn't give discrimination just using a different rating, it merely means that a small fault will cause only the outbuilding one to trip. I suspect they thought I'd put an RCBO on the whole circuit at the house end because of the route inside the house (it isn't buried in walls <50mm so is fine), therefore assumed the cable needed one, and then decided to interpret the discrimination bits strangely - I've told them I'm going to run it with just an MCB in the house to protect the cable, and then a 30mA RCD main switch in the outbuilding (it's only running a few sockets at the moment so I don't think I need to worry about RCBO'ing each circuit)...

I was at work, so didn't have my copy of the regs with me, and wanted to send a reply to the LABC today