Outdoor and indoor lighting on same circuit

[Ellsa100]

An MCB operates on over-current, it doesn't care where the current is flowing to, if there's too much current flowing the MCB will operate.

MCB's operate on Live to neutral, live to earth and live to live faults.

gotcha,, thank you.

 

[brianmoooore]

The fault current that will trip the MCB is of the order of 1000 times greater than that which would trip a RCD. Or, to put it another way, the leakage in your wiring is at least 1000 times worse than the maximum that is considered safe.

 

[timhoward]

The issue with the MCB tripping only seems to happen when I turn on the garden lights, so there is something wrong with that part of the circuit....

[.....] There are maybe 10 garden lights outside.

Even if you did arrange a new circuit for the outside lights, the fault would need finding anyway as things definitely won't be up to the standards required to sign off a new circuit as it stands.
A decent sparks could do some testing to work out where the issue is and I'd imagine have a good idea what is going in within a couple of hours.

One serious point - they aren't RCD protected, and there's a suspected live-earth fault. I'd suggest leaving them off until this is sorted. If they are metal then one or more of them could be in a condition that if they were touched they would cause an electric shock.

 

[Ellsa100]

Even if you did arrange a new circuit for the outside lights, the fault would need finding anyway as things definitely won't be up to the standards required to sign off a new circuit as it stands.
A decent sparks could do some testing to work out where the issue is and I'd imagine have a good idea what is going in within a couple of hours.

One serious point - they aren't RCD protected, and there's a suspected live-earth fault. I'd suggest leaving them off until this is sorted. If they are metal then one or more of them could be in a condition that if they were touched they would cause an electric shock.

Thanks for this and all replies. I learn a lot posting here (although I’m starting from a low base!).

 

[Calson]

A properly installed outside outlet with a weather cover will not have water leaking inside. It does not hurt to caulk where inside wires enter and leave the box used for the outside outlet.

In the USA there are code restrictions that prohibit doing this but it is not likely to come up in a casual inspection.

 

[PeakSteve]

But the circuit doe snot have RCB protection...I thought a MCB would not trip from simply a live to earth fault - wouldn't you need an RCB or RCBO? thanks

It depends on the type of Earth, but as long as >6A fault current can flow from L to E, it can still trip an MCB!
But as stated above, it is likely to be more than simply damp (which would trip an RCD @ 30mA, but likely wouldn't run to anything like enough to trip an MCB)