Fault finding an intermittent RCD trip

[Andrew Thomson]

Hey all, really hopping someone will be able to help me with my issue. This problem relates to my personal home, but i can't seem to figure out the issue.
Quick background. The main switchboard at my house feeds into a sub-board in my shed. This sub-board then feeds into another sub-board which is in a room separate from the house (my room). My rooms sub-board has 3 safety switches (A.C, Power and Lighting). The shed board has my room(one 32A switch), the power and lighting of the shed its self, a solar array on the roof and a grey water system, each on separate switches but all on 1 RCD.
Some days when i get home from work the RCD on the shed board will be tripped and will continue to trip at random intervals for around about half an hour and then be fine some times for days at a time.
The only things i've been able to test due to its random nature is that it isnt anything in my room as ive turned that safety switch off and it will continue to trip.
Just wondering what would be the easiest way to find the issue with this installation. Is the only real option an IR test on each circuit connected to the sheds sub board?
Hope this makes sense, thanks in advance
Andrew

 

[Pete999]

Call on the services of an Electrician Andrew.

 

[Wilko]

Hi Andrew - as Pete says, you are going to need help with this.

Solar invertors have been known to sometimes upset RCDs (when starting up in the morning for example). If it was this, all you could do would be to isolate it.

 

[littlespark]

It could be any number of things. Faulty appliance, dampness, faulty RCD itself.... or a combination of some of these where one alone doesn’t cause a trip.

 

[Octopus]

You need to isolate all the other circuits of the shed board .... With double pole isolation and see if the rcd stays on during the day .....

 

[BruvDunk]

Going to need a bit of fault finding to determine, sounds like as mentioned above call in an Electrician ..

You could try isolating the different circuits depending on your knowledge to give the Electrician a headstart but sounds probable to get a spark in to sort out.

 

[Shoei]

MODS: New here so if this oversteps the mark please delete.

It's good advice to call an electrician for this, tripping RCDs can mean something on its way out which can quickly become a serious problem. That said, you can do preliminary checking on the wiring while it's isolated and that could give your electrician a head-start, intermittent faults can be a nightmare.

RCDs trip at a threshold current and sometimes the fault is evident at a lower current. If you have a meter that can measure resistance, be absolutely sure that the wiring is isolated from the mains at your house switchboard and measure the resistance between live and earth on the isolated circuit, at your shed board would be convenient.

Typically you'll see a resistance, for example if it reads 48kΩ you have an earth leakage of 5mA which wouldn't trip the RCD. It probably trips at 30mA so if the resistance falls to 7.7kΩ then the trip will operate.

If the resistance is low, getting towards 10kΩ (say) you can disconnect circuits and appliances until the resistance increases and that can point to the problem. Some leakage is normal, for example through a computer or microwave supply.

Disclaimer: There are plenty of ways this can give misleading results so if it doesn't work just call your electrician.

 

[Octopus]

^^ very odd advice given the op isn’t a spark, so is very unlikely to have equipment and knowledge to use it .....

 

[Shoei]

Fair comment Murdoch, happy for this to be deleted if it goes too far.
In my house even my very non-engineering daughters know how to use a DVM so maybe I have a twisted view of the world

 

[telectrix]

Fair comment Murdoch, happy for this to be deleted if it goes too far.
In my house even my very non-engineering daughters know how to use a DVM so maybe I have a twisted view of the world

you must have weird daughters....how do they find the time to use a DVM in between nail polishing, doing make-up, hours in the shower, and iphone and faceache time?

 

[Shoei]

They are weird, but they're motivated, it goes something like, "Dad, my GHDs have stopped working, it's the heater part again, can you order me a new one?"

 

[Octopus]

Fair comment Murdoch, happy for this to be deleted if it goes too far.
In my house even my very non-engineering daughters know how to use a DVM so maybe I have a twisted view of the world

I always recommend people unplug as much as possible - to try and narrow down the issue ..........

a very recent one was very irregular .... so I asked the client to keep a "diary" of when it happened ............. they noticed it was when the lady of the house got home .............. and plugged in her laptop .......... one new charger later, the issue was resolved ............... and no costs for a spark!