RCD Mystery tripping

[safedepth]

Hi all,

Went to a customers yesterday to investigate a tripping RCD.

Easy, I thought, most likely to be a faulty appliance or maybe MCB or RCD.

No such luck.

All appliances switched off/unplugged. Fridge, cooker hood and dishwasher off via FCU's above worktop. RCD still trips when MCB made.

Swopped MCB with other known good one from same board, same result. Fault stays with circuit.

No new recent work, no pictures hung, no nothing!

Ring continuity good, didn't megger it though as indication of a short between L-N. Can't remember figure, sorry. Indications to me are something plugged in, buggered if I can find it though.

Going back tomorrow to unplug all appliances, start splitting ring and isolate fault.

Anyone had a similar problem?

 

[Badger]

are you sure there isnt anything points wise hiding like a spur to an outside light thats hidden behind a wall cupboard

 

[safedepth]

Hi Badger,

No to be honest I'm not sure, the customer is and he fitted the kitchen, but it was a few years ago and he may have forgotten something. It's a very tidy board, the circuit in question is labelled as kitchen/utility room sockets and sure enough that's all that appears to be on it. An extension was built 5 years ago, wired by a very reputable sparks of this manor, paperwork seen and nothing to report there.

 

[Badger]

but i didnt wire the extension :^O :coat can you get to unplug every thing, like the appliances amd do a full insulation test and also a continuity test of that circuits wiring, im asuming its a ring main?

 

[safedepth]

It looks like your work!

When I return tomorrow then I'll be pulling the plinths from the cabinets to unplug fully and do a more detailed search for the cause. It is a ring and end to end continuity is good. I'm thinking, disconnect in board, split ring at roughly half way point of ring and reconnect each half in turn as a radial then test at board. It's a start anyway. Also disconnect each switch plate and test for shorts between them, therefor breaking the ring down into legs. Longwinded that way and some of the face plate screws are dodgy but it should narrow the search.

 

[Badger]

well it must have been a top notch job then for me to have done it :^O

 

[M107]

disconnect & separate legs at cu, do the same at mid point of circuit (educated guess as to mid point) then IR both legs, odds on one will be tickety boo & the other will show a fault.

Faulty side find mid point disconnect making two legs & repeat IR as above...keep going eventually you'll find the problem section/accessory.

 

[safedepth]

disconnect & separate legs at cu, do the same at mid point of circuit (educated guess as to mid point) then IR both legs, odds on one will be tickety boo & the other will show a fault.Faulty side find mid point disconnect making two legs & repeat IR as above...keep going eventually you'll find the problem section/accessory.

My thinking exactly.

Badger, if it was you, and it's beginning to look like it was! where did you leave that bloody socket!!!

 

[septiclecky]

Could be a the RCD has gone faulty

 

[safedepth]

Could be a the RCD has gone faulty

Unlikely as it's only when the kitchen cct mcb is made that the rcd trips.

 

[Badger]

My thinking exactly.Badger, if it was you, and it's beginning to look like it was! where did you leave that bloody socket!!!

i installed one in the loft if that helps :^O and then took a 1.5mm 2 core flex to the outside pond sockets as a spur from the socket in their loft that in turn was spurred off the sockets in the dishwasher :^O i used 2 core and drove a earth rod into the hv cable and got the earth through th rod :^O

 

[safedepth]

i installed one in the loft if that helps :^O and then took a 1.5mm 2 core flex to the outside pond sockets as a spur from the socket in their loft that in turn was spurred off the sockets in the dishwasher :^O i used 2 core and drove a earth rod into the hv cable and got the earth through th rod :^O

ROTFWLROTFWLROTFWL

Quite right too, that's how it should be done.

 

[Badger]

why thankyou for agreeing with me :^O

 

[Riggy]

You went yesterday, and you're going back tomorrow, meanwhile customer has no kitchen or utility sockets? ROTFWL

The other thing to consider of course is N-E fault on another circuit?

 

[safedepth]

You went yesterday, and you're going back tomorrow, meanwhile customer has no kitchen or utility sockets? ROTFWL The other thing to consider of course is N-E fault on another circuit?

Only means they have to boil a kettle in a different room. Other work today had to take preference.

Help me more with the N-E on a separate cct fault. The only cct to trip the rcd is the kitchen/utility cct, all others fine. Is my inexperience causing me to miss something here.

Fitz

 

[Riggy]

Only means they have to boil a kettle in a different room. Other work today had to take preference.Help me more with the N-E on a separate cct fault. The only cct to trip the rcd is the kitchen/utility cct, all others fine. Is my inexperience causing me to miss something here.

Fitz

If nothing else has tripped it since you were there, I'm probably wrong, however:

Just say there's a N-E fault on another circuit. The RCD will trip when any circuit fed from the same RCD is drawing current because some of that current (<30mA) will pass via the fault to earth, rather than taking the "correct" return route via the neutral. When a house is unoccupied, except for the electrician trying to find the fault, the kitchen ring is generally the only circuit drawing any current, hence when the MCB for the kitchen ring is switched off the RCD doesn't trip, even though the fault is on another circuit. However once the customer is home and uses the shower (say) that also causes a trip.

Hope this makes sense!

 

[safedepth]

Riggy,

No other reported faults so must assume all is well elsewhere.

Thanks though.

 

[Badger]

just a thought is the boiler wired on the same circuit, could there be an earth fault on some pipework?

 

[safedepth]

No, sorry, boiler is on its own cct. As I say a very tidy board.

 

[Badger]

ok then is it protected by the same rcd :innocent