RCD intermittant tripping - how do I find out which circuit?

[sparkybird]

Hi all - need to pick your collective brains!

My RCD has tripped twice in 2 days - so a fault I think!

The CCU is less than a year old, tested out fine and everthing except lighting circuits are on the RCD side. This is the first time I have had a problem.

Nothing about the load has changed and so far I can't see a common element to what was on when it tripped. It resets OK and no MCB's have operated.

I have been having some work done in the bathroom and this has an electric plump, so would testing out the cable to it be the first port of call?

As I understand it the RCD detects an imbalance of current in the phase and neutral (ie it must be in the cpc) of more than 30 mA. So is this more likely to be a damaged cable than a faulty appliance?

If it's not the pump, how do I go about sussing out where the problem is - esp as it is so intermittant?

Hope you can help!

SB

 

[Spark123]

If the pump has a double pose isolator, have you tried switching this off and see if the problem goes away?
A 30mA RCD normally operates somewhere between 15mA and 30mA, which is where the ramp test function on some testers comes in handy.

 

[Steve]

Hi all - need to pick your collective brains!

My RCD has tripped twice in 2 days - so a fault I think!

The CCU is less than a year old, tested out fine and everthing except lighting circuits are on the RCD side. This is the first time I have had a problem.

Nothing about the load has changed and so far I can't see a common element to what was on when it tripped. fridge and/or freezer? It resets OK and no MCB's have operated.

I have been having some work done in the bathroom and this has an electric plump, so would testing out the cable to it be the first port of call? the electric plump may be a suspect.

As I understand it the RCD detects an imbalance of current in the phase and neutral (ie it must be in the cpc or someone's getting an electric shock) of more than 30 mA. So is this more likely to be a damaged cable than a faulty appliance? not nessecarily. Is your fridge or freezer getting on a bit? These wear in the carbon brushes in the motor, creating earth leaks.

If it's not the pump, how do I go about sussing out where the problem is - esp as it is so intermittant? likely to be a constantly on appliance due to the intermittency - fridge freezer. other items with old motors are suspect. washing machines, tumble dryers, other watery appliances.

Hope you can help! did my best

SB

 

[sparkybird]

Thanks for speedy replies, folks!

It looks like my guess at a faulty cable would be wrong then - more likely to be an appliance.

Problem is that I can't put any of them on the non RCD side to eliminate them! I guess that the appliance would actually have to be drawing current in order for it to trip the RCD? Ie Washing machine on or pump pumping? This might help me to narrow it down as it would then be fridge/freezer as this is the only one constantly on....

I also wondered if there is a way of testing the appliances to see which might be the problem one?

Will keep an eye out for what is on when it next goes.

Many thanks for advice
SB

 

[plugwash]

if you have a spare breaker space on the non-rcd side then you could fit a 16A breaker, wire an extention lead to it and use it to power the fridge/freezer temporerally.

 

[sparkybird]

Plugwash - you're a genius!

No spare breaker but I could temporarily make some space, so will try this out!

Cheers

SB

 

[andy]

I also wondered if there is a way of testing the appliances to see which might be the problem one?

use an insulation tester to look for earth leaks

 

[JohnD]

From my limited experience, I'd go with crafty on watery appliances. I've found they tend to have slight earth leakage and it may be a combination of things, each with a very slight leak, that together add up. Try actually unplugging your diswasher, kettle, steam iron and washing machine for a start. Only plug them (one at a time) when you're about to use them. Also think about immersion heater and boiler, though they're more tiresome to isolate in winter.

 

[threepandn]

Hi Sparkybird.
Intermittent faults can be very difficult to find.The appliance doesn't have to be switched on to cause tripping.The favorite items are usually Kettles, Irons, Washers, Fridge/Freezers.Microwave. I would suggest you unplug all items when not in use. If this solves your problem restore each item one at a time but always leave the last one you have checked disconected.One sure way to check equipment would be to have your equipment PAT tested.Keep us posted with the outcome.
Regards.
Threepandn

 

[sparkybird]

Thanks everyone - you're all electric detectives!

My washing machine is getting on a bit, and was on the second time it tripped (didn't check the first time) so will try this as a first port of call.

I also had two computers on both times and recall something about computers and high cpc currents - am I barking up the wrong tree

Re testing the equipment, I have an insulation resistance tester - can use this to test the washing machine? If so, how would I go about this - testing at say the plug top? I thought that the high test voltage used could damage the electronic components??

Once of my college mates has just done his PAT testing, so might have a chat to him

Thanks again

SB

 

[plugwash]

Thanks everyone - you're all electric detectives!

My washing machine is getting on a bit, and was on the second time it tripped (didn't check the first time) so will try this as a first port of call.

I also had two computers on both times and recall something about computers and high cpc currents - am I barking up the wrong tree

yes, well worth checking out. computers generate some earth leakage in normal operation (though it shouldn't be significant unless you are running them by the roomfull) but they also have some pretty big filter capacitors arround and if those fail then earth leakage can skyrocket.

Re testing the equipment, I have an insulation resistance tester - can use this to test the washing machine? If so, how would I go about this - testing at say the plug top? I thought that the high test voltage used could damage the electronic components??

afaict the normal way (and what pat test units do) is to link live and neutral together and then test between the live/neutral pair and the earth wire. if your insulation resistance tester has an option to test at 240V then its probablly worth using it at least to start with.

This may not catch it however as the leaky part may not be switched in unless the appliance is powered up so a run test with leakage being measured is pretty important too and i can't really see how you can easilly do that without a pat tester.

Once of my college mates has just done his PAT testing, so might have a chat to him

good idea