Discuss RCD Random Tripping in the Electrical Forum area at ElectriciansForums.net

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charlie76

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Evening all. Just after a bit of advice. Just been out on a job where they have had Random tripping of one of the RCD's on a split load board. They were told by a previous electrician it was the shower so that got replaced, problem continued. Another electrician said they had a cracked shower pull cord box and damp was getting in so he replaced that. Another replaced the RCD and the saga continues and I got called in.

Last night, mulling over my options with the info I had I though it sounds like a N-E fault so i'll megga all circuits and see what I get. Anyway all about what you'd expect for the age, although ring circuit was down to 40MΩ. Oven circuit >999MΩ N-E however with the oven back in circuit 7MΩ N-E. Although not a fail would you say this would be low enough to give intermittent trips of an RCD when under load. Funnily enough they could not replicate the problem tonight but they are convinced it has happened when they have had the oven on. Also to note when I removed the front plate of the 45A oven switch the line feed fell out and was not screwed down at all, could this have caused the RCD trip?

Any tips would be appreciated, i'm back there saturday...

Also to note RCD tests are fine and ramp test no apparent issue with the RCD and in any case has been replaced.
 

westward10

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7 Meg ohm will not trip an rcd however there maybe a fault with the oven which only occurs when it is operating. A loose connection can cause an rcd to trip so maybe you have hopefully resolved the problem. Don't take for granted it is the oven just because the householder is convinced it is the cause.
 

mattg4321

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Fridges or freezers are always worth a look. Try plugging it into a socket on the other rcd for a few days and see if the tripping then affects that rcd. These intermittent faults are always a pain.
 
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charlie76

charlie76

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Whats the issue with fridges and freezers? I've heard this before? Any test other than plugging it into the other half of the board to confirm?
 

bigspark17

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An earth leakage tester will help if you could earth leakage test at cu all circuits! Google earth leakage testers!
 

UKMeterman

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Hi,
You DO need an earth leakage tester to fault find this, any appliance with an earth connection may legally leak up to 3.5mA through the mains filters and you will not see this on a megger test. A 30mA rcd must trip between 15mA and 30mA.
 
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charlie76

charlie76

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Thanks folks. I'm going to invest in one. I think you are right i'm not going to accurately diagnose this without an earth leakage tester.
 
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charlie76

charlie76

Regular EF Member
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Hi,
Have a read www.beama.org.uk/asset/7EE14AAB-81DB-4870-A9ACFBC5C58A94A2/
Thanks mate, i'll have a read, looks very in depth but should be a useful bit of reading.

Anyway, not wanting to spend an arm and a leg on one, I watched a review and video on youtube and have ordered one of these:
Just shy of £80 with next day delivery. I'm back at the customers Saturday so i'll post back here how I get on.
 

LED Lighting

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I have had this before. It will definitelybe an appliance but which one is the question.
Ovens when they heat up is a common one, tumble dryer and washing machines half way through their cycle again is a common one.
How I do it is
Put a long cable from the CU MET to a stand alone met
Move all bonding to that met
Clamp the long length of cable
stick several appliances in at the same time
Wait till you get some current on the Clamp (only a few ma) then start dropping circuits till you identify the circuit
Then break that circuit down (appliances) till you find the offending item
 

westward10

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Bit
I have had this before. It will definitelybe an appliance but which one is the question.
Ovens when they heat up is a common one, tumble dryer and washing machines half way through their cycle again is a common one.
How I do it is
Put a long cable from the CU MET to a stand alone met
Move all bonding to that met
Clamp the long length of cable
stick several appliances in at the same time
Wait till you get some current on the Clamp (only a few ma) then start dropping circuits till you identify the circuit
Then break that circuit down (appliances) till you find the offending item
Bit lost, what is the long length of Cable?
 

HandySparks

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I have had this before. It will definitelybe an appliance but which one is the question.
Ovens when they heat up is a common one, tumble dryer and washing machines half way through their cycle again is a common one.
How I do it is
Put a long cable from the CU MET to a stand alone met
Move all bonding to that met
Clamp the long length of cable
stick several appliances in at the same time
Wait till you get some current on the Clamp (only a few ma) then start dropping circuits till you identify the circuit
Then break that circuit down (appliances) till you find the offending item
Usually easier to just clamp around both tails together. After all, it's the differential current in the supply that an RCD is actually detecting.
 
T

The Ghost

I use a short extension lead with the earth looped out so I can clamp it the see what is leaking when I plug in.
 

Deleted member 9648

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Hi,
You DO need an earth leakage tester to fault find this, any appliance with an earth connection may legally leak up to 3.5mA through the mains filters and you will not see this on a megger test. A 30mA rcd must trip between 15mA and 30mA.
Been in the trade nearly 40 years, fault find RCD tripping issues every week. I don't own an earth leakage meter and am not planning to buy one. Useful yes....essential no.
 

robmiller69

New EF Member
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Massive pain in the ****. I've just been back to an intermittent fault on a new build. In the end, the ramp test on the rcd was low but not out of the spectrum just very very low. I replaced and the nuisance has gone.
I'd guess there's a fault on an appliance rather than any actual circuit. 1meg and under is a fault(it used to be 0.5meg by the way). If your getting 7meg that's a good reading.
Anything over 50megs fantastic.
There's been a lot of rain again, is it something external, only causing an issue when it rains.
Good luck.
 

robmiller69

New EF Member
Messages
4
Massive pain in the ****. I've just been back to an intermittent fault on a new build. In the end, the ramp test on the rcd was low but not out of the spectrum just very very low. I replaced and the nuisance has gone.
I'd guess there's a fault on an appliance rather than any actual circuit. 1meg and under is a fault(it used to be 0.5meg by the way). If your getting 7meg that's a good reading.
Anything over 50megs fantastic.
There's been a lot of rain again, is it something external, only causing an issue when it rains.
Good luck.
 
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