Can't test RCBO as main RCD trips first - what to do?

[Jimmy Boy]

Yea I would go with that, but OSG doesn't prohibit 'Metal' enclosures as long as the tails are mechanically protected, I guess fed in to the board in conduit or similar.

ATB J

 

[Guest55]

Im fairly certain that metal CU's were / are prohibited for domestic TT installs.
Cant remember the reg , might even be from the 16th regs.
Its just something that i remember reading somewhere.

 

[Jimmy Boy]

Yea I can't find it in the BGB only the OSG Green page 30 still thumbing the BGB
J

 

[Engineer54]

I don't disagree with extra protection I was just curious to see if it was an interpretation of the regs or a reg
Eng 54 could you explain to me how you interpret the regs on protecting tails in to an enclosure on a TT ? if the 100mA RCD is in the board, and not external to it how does/can it protect the tails that are from DNO fuse to incomer on RCD ? Not a trick question just a genuine enquiry fella.

ATB J

To be honest with you, for the life of me i cannot understand why you would need an RCD to protect the insulated and sheathed tails entering a metal CU/DB on a TT installation!! If the installation is correctly installed by a competent electrician, that suitably ''Bushes'' the entry of any tails entering a metal CU/DB, ...why would you need protection from an RCD??

I'm not the best person to ask for interpretation of BS7671 regarding TT systems. As to my mind, that whole section needs completely revamping in it's entirety... lol!!

 

[drew35]

I would have thought you could have gunned the RCD out and stuck a main switch in from stock in about thirty seconds, tested the RCBO, and then gunned the RCD back in. If you were that worried.

 

[ackbarthestar]

I think it relates to normal leakage currents and high Ze(Ra) resistance. A voltage, albeit small and non existent to dry hands/bodies fully clothed, will be constantly present.

I have measured up to 27V, excessive, between earth and MET before now without the RCD tripping.

When/if a fault develops then you are looking at a potential divider created by a small R1 with a very large Ra but then that's what the RCD is for....