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 Post subject: RCD Tripping under load
PostPosted: Fri Apr 16, 2010 10:30 am 
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I'll try and give you the full story here, so bear with me if it looks like an epic.

For the impatient, the summary is this: last night the RCD tripped out while I was using an electric drill. None of the MCBs tripped. From that point on, as soon as I apply a load to any socket the RCD trips again.

Right. From the top. I have been refurbishing my kitchen over the last couple of months.

Structurally, I have had a wall taken down to open the kitchen up into a pantry area - no electrics were involved.

Electrically, I have taken one spur off an existing double socket and fitted an SFCU and terminal box ready for the extractor hood, and another off another existing socket to supply power to the new built-in gas oven.

Neither of these new appliances are wired in as yet, and the cables have been earthed to the terminal boxes and the live and neutral wires fixed into connection blocks.

Other than that, I have replaced all the sockets and switches with new ones and I can assure you they have been fitted far better than the existing ones were.

All this work was completed a couple of weeks ago and everything has been fine.

On Wednesday I got to the point where I was fitting the wall cabinets. In a momentary lapse of concentration I managed to nick a power cable while drilling into the wall, which obviously tripped the RCD. ::b

So, amid a bunch of expletives, I dug the wire out of the wall, chopped out the damaged bit and rejoined it with connector block. I switched the power back on and everything was fine once again.

Last night I was fitting the final wall cabinet. As I started to drill the third hole the RCD tripped. Again, none of the MCBs tripped. I'm 99.9999% certain that this drilling was not in the vicinity of any electrics (once bitten and all that) and it certainly wasn't the 3rd hole that did it, as the bit had barely scratched the plaster when the circuit tripped.

At this point, I couldn't reset the RCD; it simply tripped every time I switched it on.

I went all round the house and unplugged and/or switched off everything.

At this point I should mention that I basically have four circuits in the house: 2 lighting and 2 power. There are actually three other power circuits for the shower, cooker and garage but as none of these are required they are all switched off with their respective MCBs.

Anyway, after switching everything off I was able to reset the RCD.

The first thing I switched on was the combi boiler. Everything still fine.

Next, being keen to get the job in hand finished, I picked up the drill and squeezed the trigger. *trip*

*reset*

Okay, the boy's getting a little impatient now after being unceremoniously dumped from his PS3 game. I switch on the TV socket. *trip* Switch it back off again.

*reset*

Right. Let's try something less juicy. The cordless telephone. Brilliant, that works. Next I try a micro-hifi system. That works too. I switch on the microwave, which is currently giving staunch service in the dining room, and that lights up it's clock. So I press the start button and *trip*

*reset* *trip* *reset* *trip*

I go round and switch off the few things that were on.

*reset*

B#gger! I could really do with the fridge and freezer working. *trip*

*reset*

Double b#gger!

On the plus side, I can keep the combi running, so we have heat, and the lighting circuits seem unaffected.

I should note that it doesn't matter which of the two power circuits the load is applied to, the RCD still trips. Even if the other circuit is switched off with its MCB.

Frankly, I'm stumped. :scratch:


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 Post subject:
PostPosted: Fri Apr 16, 2010 3:33 pm 
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the 1st thing i would ask is: -

what have you done with that connector block? hopefully you didn't leave that as the join?

you have a fault on the circuit. it can be any one of numerous things but i would 1st take off every socket you have put on in the kitchen as it may be a wire trapped.

it can also be caused by incorrect polarity which only knocks an RCD off when you plug something in that requires all 3 connections. some appliances don't require an earth (PS3/telephone) and so it wouldn't show up.


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PostPosted: Fri Apr 16, 2010 3:48 pm 
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Hi Rich,

Thanks for the response.

Rich-Ando wrote:
the 1st thing i would ask is: -

what have you done with that connector block? hopefully you didn't leave that as the join?

you have a fault on the circuit. it can be any one of numerous things but i would 1st take off every socket you have put on in the kitchen as it may be a wire trapped.

it can also be caused by incorrect polarity which only knocks an RCD off when you plug something in that requires all 3 connections. some appliances don't require an earth (PS3/telephone) and so it wouldn't show up.


1. It's still there - as a temporary measure, honest. :oops: *puts book down trousers*

2. I'll do that - some of them were a little tight on space, so it's a possibility.

3. I would've thought this would've shown up a long time ago if it were the case.

The biggest puzzler was that it happened out of the blue without obvious provocation.

I have to leave the office shortly, and I'm not sure when I'll have enough juice to get back on t'internet, but I'll keep you posted.

Thanks again.


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PostPosted: Fri Apr 16, 2010 7:08 pm 
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Well, as you may be able to tell, I'm up and running again.

I've loosened off a couple of the more suspect sockets. After doing some reading around, I've also disconnected the circuits that aren't in use rather than just switching them off with the MCBs. Hopefully that should eliminate any N-E leaks that they might have.

Now about that block that I patched up with. I'm fairly sure I know the answer to this, but what should I do with it?


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PostPosted: Fri Apr 16, 2010 7:40 pm 
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I think you have some options:

1: Replace the length of wire
2: Use propper crimps to join the cable
3: Replace the connector block with a proper junction box as long as it remains accessible.
4: I'm not sure, but I think you can get maintenance free junction boxes which can be buried.

J

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PostPosted: Fri Apr 16, 2010 8:25 pm 
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jg wrote:
I think you have some options:

1: Replace the length of wire
2: Use propper crimps to join the cable
3: Replace the connector block with a proper junction box as long as it remains accessible.
4: I'm not sure, but I think you can get maintenance free junction boxes which can be buried.

J


Cheers. It'll actually end up behind a cupboard, so crimps sound like a good plan. I'd rather not replace the whole length - although it happens to be the shortest one in the kitchen, it's also in a newly skimmed wall so it would be a shame to have to patch in the visible section.


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 Post subject:
PostPosted: Sat Apr 17, 2010 11:40 am 
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jez69 as we have been in contact through "PM", just to let others know incase they have the same problem: -

he found another socket shorting elsewhere. the reasons behind it taking so long to show itself without any apparent reason is usually because it can take a long period of plugging in & out to break the insulation down.

just for info for you: -

turning an MCB off will NOT stop neutral to earth shorts knocking an RCD off.


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PostPosted: Sat Apr 17, 2010 6:19 pm 
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Yes. Many thanks to Rich-Ando and jg for their valuable input.

I had a big tidy up of the consumer unit this morning; made it far less spaghetti-like.

I've repaired my cock-up with crimps and heat shrink, and hopefully I can get back to the business of fitting the kitchen. Although given the 80 year-old heap I'm living in I'm sure it won't be long before something else rears its head. This 'lectric's tricky stuff; if it can find a way it will.

If anyone wants me I'll be over at the kitchens forum, boning up on worktop jigs. Another exciting adventure awaits...


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