Falling down electrical cracks

[Vir Campestris]

10 years ago we bought this house. A bit of a project, and we had it fully rewired among other things.

5 years ago I had the horrible concrete sectional garage and "log cabin" (shed) used as a garden office replaced with a nice new building. Including of course a workshop. Wired up of course from scratch.

As the 10 years were up on the original electrical certificate, and the ins co requires an up to date one (it's thatched) we've just had it redone. Decided it would be easier to get the lot done, which we did.

The new sparky realised that there was no overload protection on the feed to the garage. Board fuse, RCB, the the wire under the drive. The other end has protection on each _circuit_ but diversity allows them to add up to more than the wire could take.

Ah well, we now have a new RCBO in the main box feeding the garage.

Andy

[John Walliker]

Why an RCBO rather than an MCB? I imagine the feed is almost certainly SWA which doesn't need residual current protection. John

[Vir Campestris]

It is indeed SWA.

The guy seemed to know what he was doing, and that's what he supplied. The cost of the device is going to be trivial in the overall bill.

Andy

[John Walliker]

I wasn't thinking about the cost but the lack of discrimination at the far end. John

[Vir Campestris]

Oh, I see.

There's certainly a chance that if I have an earth leakage fault it will trip in two places. That should be easily sorted out by turning off the main breaker in the garage, then resetting the one in the house. If it doesn't trip then it'll be in the garage somewhere. I can then try each circuit in turn. Besides I've had earth leakage protection for 5 years, and it hasn't tripped yet!

None of the garage circuits will take enough current to trip the breaker in the house. It would take a big load on two or more to do it. Pretty unlikely.

It's only about 5m between the two boards.

Intermittent faults will of course be a PITA. But then, they always are.

Andy

[Brian Gaff]

Are you saying you have two identical paths under the drive feeding the Garage wired as one big feed. Brian

[Vir Campestris]

It used to be that the only overload protection for the garage was on a per-circuit basis, and the total permitted load for all the circuits is more than the cable could take. Also that apart from the board fuse there was no protection against an overload fault in the garage feed cable itself.

We now have, in order:

Feed into house Board fuse Main breaker box with overload and earth leakage protection New breaker in main box going to old ELCB for the garage Small breaker box in the garage.

An earth fault in the garage could result in multiple things tripping, or a random one of three. But at least now it is protected against all earth leakage and overload faults, wherever caused.

Andy