RCBO keeps tripping

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15 Sep 2012
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Location
Durham
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United Kingdom
Hi all

I have a Crabtree protected dual RCDconsumer unit of which i have the following setup.

all lighting and main sockets to the house runs through 80amp RCCB No issues on this side. and the kitchen sockets lights cooker along with Bathroom shower runs through the 63 amp RCCB. the whole house was rewired just gone 1 year ago. and we have had no issues. however i received a call from the wife yesterday stating she lost power to the kitchen ( trying to explain over the phone was a nightmare) think she had plugged something in that didnt agree i told her i would look at it when i got in.

however i have found the following

switch all MCBs on the seperate RCCB circuit switch RCCB on then 1 by 1 switch mcbs on no issues. fridge and freezer runs fine. kitchen lights fine.

switch kettle on or tumble dryer or washer etc anything that takes a big load the RCCB trips.

reset as above then tried the following

turn cooker on 1 ring fine 2 rings fine 3 rings then the RCCB trips.

again reset.

turn shower on and guess what the RCCB trips.

if this had been a new install then i would have more things to think about. however the system has been running fine for 1 year with no issues.

any ideas.
 
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And you're positive someone hasn't installed anything since?

Disconnect ALL loads on the sockets.

Then run the checks again.
 
All hidden sockets?

All FCU's?

Double check then try again.
 
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all of them mate.

i know where every socket and every wire goes on this house lol
 
OK.

So, kitchen sockets, lights, cooker and shower are on the 63A RCD.

I would say there has to be an issue on one (or more if you're unlucky) of these circuits.

Try one by one turning off the non-socket circuits on this side then plugging in a load on a socket to see if it trips.
 
I had a similar fault this week, front end RCD 300ma tripping and not resetting, pulled ring fuse and it stayed in. Unplugged all appliances and replaced fuse - still ok

Plugged freezer in and it tripped- aha found it, uplugged freezer and plugged kettle in it tripped, swapped rcd and same happened

Everything unplugged, ran shower it tripped, opened shower up and found an old favourite, burnt neutral, but not bad enough to cause a fault

With shower disconnected, plugged freezer etc in, RCD stayed in, rplaced shower cable and all OK

Have a look in the shower/switch
 
Have seen similar faults before where there is a neutral-earth fault on a circuit and the supply is TN-CS.
 
All I know is that you can get the weirdest causes with tripping RCD's.
 
I'd say you have a 'neutral - earth' fault on one of your circuits......could be any circuit, by the way.

Easy enough to find with some test gear. :)
 
This one was TN-S

Sorry for not being clear, the reply was intended for the original poster.

It is possible with TN-S where the N-E impedance is very low or the TN-S network is very limited i.e. a single transformer supplying a single premises. In normal instances on a TN-S network in a town a N-E short inside the premises will tend to trip out an upstream RCD constantly regardless of what is running inside the premises.
 
Any outside stuff, lights or sensors maybe with water ingress. Shed with power and mr spider has climbed in to a socket?
 
I am confused - what are you trying to say?

What difference does the earthing method make to RCDs?

This one was TN-S
Sorry for not being clear, the reply was intended for the original poster.

It is possible with TN-S where the N-E impedance is very low or the TN-S network is very limited i.e. a single transformer supplying a single premises.
It can't be much lower than TNC-S and is, in any case, upstream of any RCDs.

In normal instances on a TN-S network in a town a N-E short inside the premises will tend to trip out an upstream RCD constantly regardless of what is running inside the premises.
Of course it will - that's what RCDs do - but not if NO current is being used.
 
In a TN-S network there is nigh on always a small voltage difference between neutral and earth caused by current in the neutral conductor from other premises along with your own. A N-E fault in the premises allows current to flow thus tripping an RCD, usually regardless of what you have running in the house.
A small TN-S network such as a single supply to a farm may not suffer the same as the N-E voltage could be too tiny.

In a TN-CS supply the neutral is at the same potential as the earthing conductor at the cutout hence in a N-E fault no current flows until something is switched on inside the premises, if this is sufficient to raise the neutral voltage enough to allow trip current to bypass the RCD then out it goes.
 

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