Downstairs Mains RCBO Tripping

Distorted Vision · Nov 1, 2024

I replaced the PIR sensor for the floodlights on the front of our house because the floodlights were staying on permanently. The issue hasn't been resolved with the new PIR sensor. Following this, the RCBO for the downstairs mains sockets on the consumer unit keeps tripping instantly. I thought it was caused by one of the two gang sockets in the kitchen because one socket had a switch which was stuck in the on position. I'm unsure how the downstairs mains sockets RCBO issue could have been caused by the PIR sensor replacement. They were separate circuits the outside lights circuit is on a separate MCB. Consumer unit is a 17th Edition dual RCD with a high integrity section (Downstairs sockets, Upstairs sockets and Cooker).

There is a two gang mains socket in the kitchen that had one of the switches in the on position so I replaced it thinking it might be causing the mains RCBO issue. It didn't resolve the issue. I've tried unplugging all downstairs appliances. Its still tripping.

Any electricians please advise why the floodlights are staying on permanently and why the mains RCBO is tripping. I'm deducing that the mains RCBO is defective. No idea about the floodlights issue.

SPECIAL LOCATION · Nov 1, 2024

From my general experience its more likely that the RCBO is functioning correctly....
i.e. it is detecting an earth leakage fault, (which could be as low as 16ma but more probably 30ma or greater),
and as you haven't actual done any circuit testing yet...
Or RCBO testing.. (or if you have you haven't told us the results)..
Then it is pretty much guesswork?

If you don't have access to, or knowledge of how to use electrical circuits testers,
such as RCD testers, Insulation resistance testers.. Then you probably need to call in an electrician..

At the most basic level seeing if the RCBO will hold on with no load wiring connected,
could be a first step without any test equipment...

But after that without proper testing, you are guessing and assuming and can end up in the trap of swapping random parts..
which is an expensive and time wasting exercise!!

Personally I would never recommend any DIY person opens up a consumer unit to do any work inside of it..

Whereas a competent person with proper test meters..
Could verify both the RCBO and the PIR functionality, and probably make good headway into resolving the actual cause(s),
all within a standard minimum 1hour call-out!

A switch stuck in the on position is unlikely to cause an RCBO or RCD to trip.

binky · Nov 1, 2024

the two issues should be completely separate. If the PIR swop failed, it's either wired wrong, of there's possibly a manual override switch.

as for the sockets, do you have a gas boiler connected to that circuit? That would also need switching off if you have. Tripping could be many things, socket screw rubbing a cable, damp in walls, steam in kitchen, sockets sprayed with cleaning products. You could try dropping all the socket fronts and looking for snagged wires, rust or loose connections, which can also trip RCBOs. If that clears the fault, replace one at a time and see if it trips again.

ProDave · Nov 2, 2024

Are you sure the outside light is not fed from an FCU from the circuit that is now tripping?

Basic rule if you have just done some work and something starts tripping, look VERY hard at what you have just done.

michael8554 · Nov 2, 2024

The premise is that the outdoor lights are powered from the B6 MCB, third to the right of the RCCB.
Does that actually switch off those outside lights?
Are the outside lights still on with the Downstairs Sockets RCBO tripped ?

Have you tried turning the RCBO on with every MCB turned off on the board ?

Perhaps the outside lights are staying on all the time because the day/night or duration controls are not correctly connected or have become faulty.
Or the lights are wired to be always on.

UNG · Nov 2, 2024

michael8554 said:
Perhaps the outside lights are staying on all the time because the day/night or duration controls are not correctly connected or have become faulty.
Or the lights are wired to be always on.

Wouldn't be the first time that an unknown switch is actually the override switch for the outside lights