Garage rcd tripping and blowing fuse

[Chris_81]

Just had a call of a friend of my Dad's. His garage wiring has been playing up for a while, tripping the rcd in the garage cu and occasionally blowing the fuse in the house (rewireable) board. Had a bloke he knows look at it for him. Plugged in a socket tester and said there's voltage there where there shouldn't be. Very technical!! He also tested the garage incoming supply at the adaptable box and got readings of:

235v between phase and neutral

3v between phase and earth

234v between neutral and earth

He disconnected the lights?! as he thought they were the problem, then admitted he was in over his head!!

I'm going round tomorrow to see what else he's done. From what I've been told it sounds like a fault on the cable from the house cu to the garage resulting in a possible reverse polarity. The cable has been in there for well over 30 years, is swa and all buried.

The fault has only been recent. What's everyone's initial thoughts on this, problem with the cable or a fault at the house cu?

 

[Andy™]

sounds like wrong polarity.

this alone would not stop anything working, so it may well have been like that 30 years since it was installed. the recent 'problem' could be a failed part, which is now tripping RCD / blowing fuse, and as a result, the wrong polarity has been discovered

 

[sparkytim]

Would expect same voltage L-N and L-E and 3 volts to be N-E if any

Maybe cable fault?

Suggest start at C Unit inside and work towards Garage.

Disconnect both ends and check continuity of conductors and Insulation resistence.

 

[Chris_81]

Exactly what I plan to do Tim. Continuity, insulation resistance then hopefully find whats wrong. I'm thinking cable fault although it certainly sounds like the polarity is wrong...

Andy, he said it all started when a washing machine stopped working so that could well be the case.

 

[NozSpark]

Could be reverse polarity

or...

L-E fault on washing machine and a disconnected earth on the supply cable??

 

[ADS]

100 % agree with Andy.

I think you'll find the SWA connection at the house CU is cross connected, giving the reversed polarity.

This will have been fine (although dangerous) for years until such time that a fault developed on the garage circuits.

If we're right, you need to correct the polarity issue, then get on with the testing that you've mentioned to rectify the fault.

 

[ProDave]

Agree with everyone else, wrong polarity. Sort that out first.

As to tripping / blowing fuses, I suspect insulation breakdown, probably a pinched cable in an accessory. An insulation test on 1000V should track that down.

 

[Chris_81]

Turned out to be a nice simple job. The swa joint in the adaptable box under the stairs had been wired in reverse, 5 min fix Tested the cable for continuity and ir, all came out ok. Tested the garage as well as it only had 3 sockets on a radial and two strip lights, all ok.

Definitely a fault with the washing machine!

 

[sparkytim]

Nice to hear a good result with out to much hassle.

 

[a1]

Thanks for the update.

 

[steptoe]

can we ask the supply type?

 

[Andy™]

TNCS! everyone is going to die!

or maybe not

 

[green-hornet]

[quote name='Andy

 

[steptoe]

[quote name='Andy

 

[Chris_81]

Supply is tns. Earth to the garage was exported using 3 core swa. Cable is old and from what was said the garage could be turned into a sort of workshop so I'm going back tomorrow to tt. (Garage is approx 20ft from the house).

Maybe seen as over kill by some but makes sense to me and the bloke is happy to have it done!