Earthing question

[MrSPV]

Hi

I had another look at my outdoor socket recently (posted about previously but still not replaced!). One of the issues with it is that the indoor 'PowerBreaker' RCD trips often regardless of what's plugged into it (consequently we don't actually use the socket). I noticed that it's earthed via the steel duct that the mains is fed through (see pics). Or at least that's how it appears to me. The steel duct on the right goes into the ground and the mains cable comes out in the void under the floor. It comes up in the under stairs cupboard where the RCD resides. Is earthing like this normal and might it be the cause of the constant tripping?

Thanks
Mike

 

[JohnD]

No. The RCD compares the current of electricity going through the L and the N wires. It should be the same (going in equals going out). If they are different, it trips. it will do this regardless of the earth.

The much more common fault causing an outdoor circuit to trip, is water getting into the parts somewhere, usually from rain.

i can see your box, wiring and socket are rather old and dirty. Possibly a new box without the crack, and a clean new socket, would help. What are those spare wires in the box? Lift up the black one so that even if water gets into the box, it will not get the connector wet.

Show us your "indoor 'PowerBreaker' RCD" please

 

[EFLImpudence]

I noticed that it's earthed via the steel duct that the mains is fed through (see pics). Or at least that's how it appears to me.

It doesn't look like that.

The earth wire is connected to the wire armour of the cable; not the conduit(duct).

 

[ericmark]

As @JohnD says, I would use petroleum jelly on all mating services, this is good at sealing for water ingress. And small hole at bottom so any that does get in and drain out.

 

[MrSPV]

Thanks All.

@JohnD The wires on the left go to a shed and have been disconnected for many years. The plan is to replace the socket but I'm curious about the trips. I've uploaded a photo of the 'powerbreaker'. I did some tests in the summer when it was dry and had been for several days. The inside of the box appeared dry but I guess I can't be certain what it was like right inside the socket. Just plugged in an extension lead and connected a lamp running in the kitchen all day. It tripped several times over a period of a few hours.

@EFLImpudence - yes I see that now. That's still normal I take it?

Cheers
Mike

 

[chivers67]

Disconnect the Cable that feeds the socket from the RCD. Connect a short lead up to it with a surface mounted back box & socket so you can test it indoors and see how it fairs. It could well be there is water ingress inside the SWA inside the Conduit and is causing a Low insulation Resistance that occasionally dries out for prolonged dry weather. Could do with a Yellow ring crimp on the Earth Cable underneath the Screw inside the Outdoor Socket but it's not a total disaster.

If the RCD doesn't trip then it may well prove the fault onto the Armoured Cable but you need an insulation resistance tester to check it properly. Seems a bit odd to run armoured cable through a Metal conduit.

 

[RF Lighting]

It’s possibly not the greatest installation, but nothing there looks especially out of the ordinary, and certainly shouldn’t cause any issues that would cause your RCD to trip.

If I were investigating this, my first two checks would be the insulation resistance of the cable to make sure it hasn’t become damaged, and secondly to check the RCD is functioning properly and tripping at the specified ratings.

Unfortunately both these tests require proper test gear, but would very quickly rule out a lot of possible causes.

 

[MrSPV]

Thanks everyone for your help. Looks like I'll be calling an electrician for this.
Cheers
Mike

 

[MrSPV]

Disconnect the Cable that feeds the socket from the RCD. Connect a short lead up to it with a surface mounted back box & socket so you can test it indoors and see how it fairs.

I have done this now. I ran it for 3 days. On day one it tripped several times. Only once on day two and three. It also appears to trip when there is nothing plugged in to it. The RCD is fed by a circuit breaker in the consumer unit which also feeds the house alarm (see image). Do the circuit breaker and the RCD do the same thing? In which case is the RCD needed?
Thanks

Mike

 

[chivers67]

O that's not good then. It appears you have some kind of Earth leakage fault elsewhere not connected to your outside cabling.

An MCB normally protects your circuits from Overloading or Short circuits.

As per John's post above ^ . The RCD "monitors" current so a big enough imbalance on a circuit will cause it to trip or when there is a current leakage to Earth somewhere as instead of current returning though the RCD via the neutral it takes another route to earth.

An RCD is required for many circuits especially Sockets outside as it reduces the Risk of electrocution

 

[MrSPV]

Thank you. So if the RCD is not at fault then I guess I could connect another one - perhaps a plug in one such as the one I use for the mower - and expect it to behave in the same way?

If it's an earth leakage fault 'elsewhere' does that mean it could be anywhere within the house?

Thanks
Mike

 

[ericmark]

Sorry suck and and see is not really a good method, you need to test, cost me £35 for an insulation tester, not calibrated but that does not really matter, as long as a 500 volt range.

 

[chivers67]

Thank you. So if the RCD is not at fault then I guess I could connect another one - perhaps a plug in one such as the one I use for the mower - and expect it to behave in the same way?
If it's an earth leakage fault 'elsewhere' does that mean it could be anywhere within the house?
Thanks
Mike

The Fault could be on Any of the circuits fed off the RCD that is Tripping. It needs to be localised. I'd tend to start with any circuits that have likely become damp such as an outside light or a circuit running through a kitchen or bathroom.

 

[333rocky333]

Power breaker sockets, i recall trip to off if they have a poor supply earth, maybe the spurs are designed the same