Main power switch tripping

[Johnmcb]

Hi all,

Wondering if anyone has any idea whats going on in my new (old) home. Basically I was using an angle grinder tonight and the main power for all the sockets, cooker etc went off and I thought that maybe just tripped or a fault with the grinder. Anyway went to check the CU and nothing had tripped but the main power with the test button had switched to the off position. Tried to turn it back on but i switched it on and it immediately switched back off.

I've double checked all the sockets I've changed and they seem fine. The socket the angle grinder was in was an original socket. I also had the fridge in this for a few days and it did the same thing but I could switch the main power back on no problem.

Am I going to have to get a electrician with an insulation tester or something? Or is there anything else I can try?

Pic attached of CU

Cheers!

John

 

[skenk]

Did you actually unplug the grinder or just switch it off? Given the fridge was also causing the RCD (I assume) to trip when using the same socket, aside from that (unplugging the grinder), all I'd suggest short of calling an electrician is, if you are competent, to (safely-with the power off) open up the suspect socket and see if there's an obvious problem (wire trapped by fixing screw, heat damage etc). RCD's are sensitive so it doesn't take a major fault to trip one. It would be better if you had more than one RCD for protection of all your socket circuits.

 

[Johnmcb]

Sorry yes I unplugged everything in the whole house. I also checked the suspect socket.

Could the load from the angle grinder have weakened an already weak spot in the ring?

 

[ericmark]

As already pointed out the thing with the test button is called a RCD although also some other names and it works on both live wires the line and neutral, but many items only switch the line. So step one is to switch off all the breakers for that RCD then try to reset it, once reset then turn on each breaker. But if it still trips then unplug every thing as the breakers don't switch the neutral.

I had to hunt for a fault in my daughters house. It was the screw holding the socket on the wall which had trapped the neutral wire. So every thing would switch on, but any load and it would trip.

 

[ericmark]

Sorry yes I unplugged everything in the whole house. I also checked the suspect socket.

Could the load from the angle grinder have weakened an already weak spot in the ring?

Unlikely but vibration could have caused a screw to touch a wire causing a problem. With daughters house some one had caught the neutral with a knife when fitting the socket and there was just a little bare copper which the socket hold down screw had touched, the smallest movement could have changed it to not touching.

In my house I also have very old RCD's and I always need to switch off breakers before resetting RCD. Theory should make no difference but in practice it does.

 

[skenk]

did you grind a cable!? You can try dismantling the (apparently) faulty circuit (although it could be a coincidence and actually another circuit is faulty). Also will the RCD reset if the breakers are all switched off? Also have you tried turning the RCD lever all the way off then on? I'm not familiar with that kind of RCD you have there, some need pushed in the opposite direction until click before they will reset.

An electrician can test to locate a fault on a cable but likely an insulation resistance tester needed, and someone who knows how to use it.

 

[Johnmcb]

Thanks for all your replies, I drove out to the house this morning to check a few things mentioned above still no joy. I did turn off the breakers and try again multiple times last night but with no luck. There's also nothing plugged in at all, we're not living in it just now so that's easy.

I might check every socket in the house before calling an electrician. Also I did not grind through a cable...

Thanks again for tips, I'll update this thread with my progress...

Heres some images. http://imgur.com/a/IXRyF Why do some knockout boxes have the earth screwed to them?

J

 

[Johnmcb]

Hi again - how much would you say is reasonable price for an electrician to look into sourcing the fault? I'm in the Glasgow area.

EDIT - Getting the CU replaced for £250, seems good to me and happy to have that old one replaced anyway!

 

[Taylortwocities]

When having a CU replaced, the first thing any electrician worth his salt will do is to test the existing system. A hard fault like you have will be indicated at the first test!

The cost of fixing it is dependent on how easy it is to find the problem and to fix it. I would have said 2-3 hours guestimate...

 

[Iggifer]

£250 sounds very cheap for a board change to me with a full test+inspect

 

[Taylortwocities]

He did say it was Glasgow! Didn't know they had electricity up there yet........

 

[deadshort]

That CU is built too last, not like the crap built now. What is the single switch fuse under the CU serving ? If it's not connected directly to the meter it may be connected into the RCD,have you switched it off ?

I personally would not replace that CU,spend the money getting an electrican to find the fault.

DS

 

[Johnmcb]

That CU is built too last, not like the crap built now. What is the single switch fuse under the CU serving ? If it's not connected directly to the meter it may be connected into the RCD,have you switched it off ?

I personally would not replace that CU,spend the money getting an electrican to find the fault.

DS

I have no idea what it is feeding, you've put me off replace the CU now! I thought the newer ones would be up to today's standards? And this not?

 

[deadshort]

You have two rcd's if they are 30ma trip and are operational why replace ? The enclosure us metal, that's 'the new standard'
As has been advised get an electrician out to locate the fault and test the rcd's they will also advise you if the earthing of the property is satisfactory. You may require to increase the csa of the earth from 6mm to 10mm to comply with 'new standards'.

Regards,

DS

 

[skenk]

Per above, if replacing the CU, there's not much point getting another dual-rcd one, you'd be wanting individual RCBO's. Getting that in decent quality gear and proper testing is nigh on impossible for £250 for the 8 circuits it looks like you have (and that doesn't cover the fault repair)?. It could be a faulty RCD though and the old part might not be easy to obtain.

Where about in Glasgow are you? I would charge £50 fixed price or more depending on where in the city the property is in relation to Kelvinside and any parking/access issues. That includes finding the problem but not the repair (unless it's something simple like a blown fuse) which I might or might not be able to do there and then (depending on the problem) and in either case able to give you a quote for coming back later to do the repair and/or other work.

If you've already got all the sockets hanging off, now might be a good time to replace them if they're paint covered, worn/knackered. Money better spent than replacing metal dual-rcd board with same, if using decent quality faceplates.