Is something shorting my garden lights circuit?

[Yukster]

The main RCD tripped a couple of times a few days ago when it was raining. The only reason I could think of is that it is to do with the garden lighting. I switched the lights off and the RCD stopped tripping so it was a lucky guess!

I have two questions: why didn't the fuse for the garden lighting trip but the main RCD did? And what would be the likely cause of the fault, and the best method of finding and fixing it?

Thanks in advance for your help

 

[EFLImpudence]

I have two questions: why didn't the fuse for the garden lighting trip but the main RCD did?

They detect different faults.

And what would be the likely cause of the fault,

From what you say; water causing small current flow between Live and earth - more likely where dirt has gathered or insects/spiders/slugs etc.

and the best method of finding and fixing it?

Look for the above.

 

[winston1]

Fuses don't trip, they rupture. Are you sure you have a fuse and not MCB which do trip?

RCDs and fuses or MCBs protect against different things.
RCDs protect against unbalance usually caused by earth leakage such as water ingress. Fuses and MCBs protect against overload.

So to answer your question the fuse did not rupture or MCB trip (which do you have?) because there was no overload. The RCD tripped due to leakage probably due to damp getting in.

 

[EFLImpudence]

Imbalance

 

[Harry Bloomfield]

The main RCD tripped a couple of times a few days ago when it was raining. The only reason I could think of is that it is to do with the garden lighting. I switched the lights off and the RCD stopped tripping so it was a lucky guess!

I have two questions: why didn't the fuse for the garden lighting trip but the main RCD did? And what would be the likely cause of the fault, and the best method of finding and fixing it?

Thanks in advance for your help

RCD's work very differently to MCB's and serve a different pupose. You MCB trip on too much current flowing between L and N. Your RCD trips on a difference in current flow when comparing L to N, making an assumption that the difference must be flowing via the earth - in other words a fault either between L and E, or between N and E.

 

[Yukster]

Fuses don't trip, they rupture. Are you sure you have a fuse and not MCB which do trip?

RCDs and fuses or MCBs protect against different things.
RCDs protect against unbalance usually caused by earth leakage such as water ingress. Fuses and MCBs protect against overload.

So to answer your question the fuse did not rupture or MCB trip (which do you have?) because there was no overload. The RCD tripped due to leakage probably due to damp getting in.

I've got an MCB. Thanks very much for explaining