Trouble shooting an RCD protected circuit

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Hi,

I have a 3 bed Terrace property that has been rented and on the day the tenant moved out half of the electrics failed.

Modern fuse box, 2x RCD's each with 6 MCB's

One RCD wont reset & the RCD's have been swapped and the problem isnt with the RCD.

This RCD has;
MCB's for Oven, Hob
Socket circuit (all) that has extractor and boiler hard wired (No "plugged" appliances connected)
Downstairs lighting circuit

The house is empty and an electrician is coming Wednesday.

In the meantime I'm wondering what the method of trouble shooting maybe an option as I would like to be able to do some hoovering / light diy in the place? Is this just visual, open light fittings then if that isnt obvious, hard wired appliances, then wall sockets etc.

Either way I'll get the sparky to inspect but whilst its off is there something I can check as per above ?

Cheers,

Richard
 
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In the meantime I'm wondering what the method of trouble shooting maybe an option as I would like to be able to do some hoovering / light diy in the place? Is this just visual, open light fittings then if that isnt obvious, hard wired appliances, then wall sockets etc. ... Either way I'll get the sparky to inspect but whilst its off is there something I can check as per above ?
Assuming that you have already tried turning off all the MCBs, all else you can really do is to disconnect as many loads as are possible from circuits protected by that RCD - unplug everything which is unpluggable (it sounds as if you've already done that) and switch off everything hard-wired that is switchable (although that may not be foolproof if the switches are single-pole). That just leaves hard-wired things without double-pole switches, and it's probably best to let the electrician disconnect them as necessary. Does the sockets circuit supply anything outside (and, if so, can that be switched off?) - water in outside fittings is a common cause of RCD trips.

Kind Regards, John
 
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Hi,

I have a 3 bed Terrace property that has been rented and on the day the tenant moved out half of the electrics failed.
That would make my suspicious that he has removed/unwired something and that has casued the problem.

Yoiu first need to try and identify which circuit it is that is causing the problem. Often, you can do this by turing all of the MCBs off and seeing if you can then reset the RCD. Turn the MCBs back on one at a time and see which one makes the RCD trip.

If the RCD will not reset with the MCBs all off then there may be a neutral/earth fault. This may need work in the consumer unit to trace, and I would leave that to the sparky, if you dont know what you are up to!

Try the above and let us know.
 
Often times ovens love to trip RCDs, but unlikely unless you have the oven switched on.

I guess it's worth checking it's turned off at the isolator if you have one

I wouldn't release the deposit from the DPS until the spark has found the fault though
 
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As John has said , when searching for a fault that trips an RCD it is essential to isolate both Live and Neutral

This is necessary because a Neutral to Earth fault on a circuit can still cause the RCD to trip when the MCB for that circuit is switched OFF. The trip will happen when a load on another circuit is switched ON


If the fault is high resitance Neutral to Earth ( such as a water logged socket or lamp ) then only a small percentage of the neutral flows through the fault and only when a large load such a cooker or shower is switched will the RCD trip. Hence people assume the cooker or shower is responsible when it isn't
 
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Thanks for the quick replies guys.

The MCB's on that half of the box dont have any effect, when switched off the RCD still wont reset.

There are 2 external power sources but both are run from 13amp plugs and both are disconnected.

The Neutral/Earth scenario sounds likely so it will probably need the sparky to have a look at that as I'll do a quick visual inspection of most things ( I have removed the cover of the consumer unit ) but I dont know how to trouble shoot this scenario.

The other think I'll probably do is check the light fittings, open the cealing roses etc to check for anything loose as they may have had shades etc on them tha they have removed. I'll also check for isolators for the oven etc.

It doesnt sound like there is much more I can do in isolation.
 
The MCB's on that half of the box dont have any effect, when switched off the RCD still wont reset.
In that case, as has been suggested, and as you go on to say, the most likely cause is a neutral-earth fault somewhere. However, as bernard said, that will almost always only cause an RCD trip if there is some load on the installation. Have you tried switching off all the MCBs (including ones on the other RCD) and then seeing if you can reset the RCD?

P.S. One thing I forgot to say at the start. Some RCDs cannot be reset unless you first push the lever right down (as far as it will go) - have you tried that?

Kind Regards, John
 
Thanks John, I belive I have done both with no joy but I will double check
Fair enough - but if you cannot reset the RCD when all MCBs (protected by both RCDs) are off, that would be rather strange. Do I take it that there are no other consumer units or other things feeding circuits in the house? It's very much a long-shot, but the one other thing you could try would be (with all MCBs off) to switch off the other RCD, and see if you could then reset the tripped one.

Kind Regards, John
 
What about trying with the Main Switch off?
True, that's the ultimate - but if it's just a dual-RCD CU (with no non-RCD ways), then switching off both RCDs (one already off, without choice!) ought to achieve the same thing.

Kind Regards, John
 
Again pretty sure I have tested these scenarios but I will double check.

I spent an hour there yesterday going through pretty much every combination, including I belive all of the above.

I went as far as to swap the two main RCD over in the consumer unit and the problem stayed in the same location, I also removed the MCB's on the faulty side one at a time to see if that changed it and it didnt.

I'll print of this thread and run through the scenarios you mention.
 
Just for reference this is the unit
 

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It's very much a long-shot, but the one other thing you could try would be (with all MCBs off) to switch off the other RCD, and see if you could then reset the tripped one.
I presume you are just 'trying everything'.

There's no way that current on the 'other side' could cause the tripping without also tripping that RCD, is there?
 
Again pretty sure I have tested these scenarios but I will double check. ... I spent an hour there yesterday going through pretty much every combination, including I belive all of the above. ... I went as far as to swap the two main RCD over in the consumer unit and the problem stayed in the same location, I also removed the MCB's on the faulty side one at a time to see if that changed it and it didnt. ... I'll print of this thread and run through the scenarios you mention.
Fair enough - this is getting to the 'very mysterious' stage! You might as well initially bypass all the other things mentioned and, as EFLI suggested, turn off the Main Switch and see if you can reset the RCD. If you can't reset it, then there's no point in your trying anything else, and I think that would be the stage that you should 'give up' and hope that your electrician is good at diagnosing 'very mysterious' faults!

Kind Regards, John
 

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