ELCB trips

[justino]

I'm on a TT system through supplying cables that run underground, but then along the front of the house just above the front door.

I have an ELCB which trips ocassionaly, and when it does it is sometimes difficult to get it to re engage. Because of this I have been meaning to replace this or the CU which is an older wylex with the fuses replaced by mini MCB's. From memory the earth measured 17 ohms at the CU.

Whilst on holiday the ELCB tripped, and was only noticed when my neighbour popped in to move the post, and he realised the lights didn't work. He couldn't get the ELCB to turn back on as there is quite a knack to it. In an attempt to save my freezer contents I asked a friend to have a quick look, and he tried to fit a 30ma RCD in place of the ELCB. This tripped out immediately, so as a temporary measure the ELCB was refitted which he managed to get it to turn back on.

When I got back I got a 100ma RCD thinking that would work ok rather than the more sensitive 30ma. However this tripped again immediately the power was turned back on, so I have a problem somewhere which I need to sort.

I've now decided I would like to get the CU replaced, but I am reluctant to do this until I have found the fault (s) causing the trips, or at least narrowed it down.

Yesterday I decided I would see if I could narrow down the problem circuits. The difficulty with this is that it has a single ring main for both floors, another for the lights, a 3rd for the hob and immersion heater and a 4th for the outside light, so even narrowed down it would still be quite a broad area.

What I discovered was that on the lights, if I turned on the lounge lights the RCD (100ma) would trip. This is a two way switched circuit, with one switch being a dimmer. The bathroom lights would also trip the RCD. These are controlled by a ceiling mounted PIR. All other lights were ok.

On the ring main, as soon as the MCB was switched on it tripped the RCD. I was running out of time so wasn't able to unplug everything, and so decided to leave it for another day.

What is puzzling me is that I have numerous faults which I know is a possibility, but I was speculating I may have one fault that is causing this behaviour.

My friend is coming back to meg the cables which he couldn't do whilst I was away as he didn't know where every socket was in the kitchen so didn't want to risk damaging any appliances.

Apologies for the long first post, but suggested ideas for causes would be appreciated. Could the TT system be a factor? Central Networks charge £150 to change to PME, although I haven't checked if I could actually get this at my property.

Justin

 

[grandad]

Justin
Having a TT system is not the problem, in fact 17ohms ZE is pretty good and well within limits.The RCD is only doing its job by disconnecting in fault conditions.
sounds like you have an old installation and you really need to arrange for a periodic inspection by a qualified electrician to sort it out, you appear to have multiple problems that will only get worse if you leave them.
as for the causes! it could be anything from rodents,immersion heater element, trapped cables to nails in wall or incorrect connections. you will only find out if you have a proper test

 

[justino]

Grandad,

Thanks.

Yes I'm going to get it sorted, I just wanted to try and narrow issues down before I get someone in to look at it.

I think I may have fixed the issues.

On the lighting problems I have replaced the dimmer and PIR with switches. The PIR had a neutral connected, but the switch hasn't.

On the ring main I have checked every socket in the house to ensure it is correctly wired, and nothing lose. Everything looked ok, except one double socket behind a bed was full of dust and fluff. I have brushed and hoovered this out with a battery dyson. Sods law as this is the only socket that has not been replaced in the house because it is out of sight. I'll replace later.

I have put the 30ma breaker in, and so far everything is holding together with no trips. I have reconnected every appliance and turned it on, and it hasn't tripped yet.

Could the dust and fluff been the cause of the ring tripping allowing leakage to earth?

Justin

 

[Spudnik]

On the lighting problems I have replaced the dimmer and PIR with switches. The PIR had a neutral connected, but the switch hasn't.


Justin

Sounds to me like there could be a borrowed neutral somewhere for the PIR sensors.

This would only rear its ugly head in the evening when in use.

Just a thought.

 

[justino]

Even if it is a borrowed neutral, would that have caused a front end RCD to trip?

I can understand that it could cause a circuit RCD to trip, but not a whole house RCD as that is just measuring what comes in against what is going out, and what neutral path it takes in the circuits, I would have thought is largely irrelevant.

 

[Spudnik]

Good point!

Sorry i was on a different wavelength when i posted

The only thing i can suggest is, like you said, an IR test and continuity test between all conductors and see what you get.

It could be anything from a faulty light fitting, PIR, damaged cables.

The above tests should bring you closer to the problem.

All you have to do then is find it.

 

[Des 56]

It may not be installation related
By not unplugging everything,an appliance with a neutral earth fault plugged into a single pole socket could be the cause of the various problems
With the neutral earth fault on this appliance any load may be enough to trip the rcd or elcb if it is just hanging in there with the existing leakage current
The tests to be taken should shine the light for you

 

[justino]

Well since last posting I have refitted the dimmer and PIR sensor, and the 30ma RCD no longer trips.

The PIR again was full of dust which I have cleaned off. No idea on the dimmer, but it is working ok now. It is only a few years old, and perhaps was a poor conection to it. No obvious signs of cables shorting etc.

I have had everything on in the house, and so far it has held, so fingers crossed.

So has anyone else experienced dust and general fluff in a fitting causing a drain to earth?

 

[justino]

I have now replaced the socket, and out of curiosity decided to take the old socket apart.

I attach a picture I have taken.

You can quite clearly see the scorch marks on the earth bar, and the build up of dust and dirt. Also there is quite a lot of grease which looks as if it could act as a short circuit route.