RCD Tripping Intermittently

[Ciaran Lang]

Hi,

I have a RCD in the CU connected to 2 x socket circuits (house and kitchen/heating), shower and cooker. This tripped the other night when only the heating and a couple of sockets were on. I reset this and the issue only reoccurred tonight. The RCD would not switch on until the kitchen/heating breaker was off. I thought this was the issue so when I turned the breaker back on I expected the RCD to trip but it stayed on. I tried switching everything off and back on one by one but nothing tripped the RCD.

I discovered that if all the CBs are on the RCD will turn on sometimes but trip when turning on other times. By that I mean repeatedly turning it on until it stays on.

Dos this this sound like a faulty RCD? I am going to buy one to rule this out.

Could it be any other issue?

Thanks in advance for the help

 

[trev]

Ciaran, are you an electrician? Genuine question.
If not, I;d get one to test the circuits and the RCD properly. You're guessing and a consumer unit is no place for the uninitiated to be poking around in

 

[Leesparkykent]

Hi,

I have a RCD in the CU connected to 2 x socket circuits (house and kitchen/heating), shower and cooker. This tripped the other night when only the heating and a couple of sockets were on. I reset this and the issue only reoccurred tonight. The RCD would not switch on until the kitchen/heating breaker was off. I thought this was the issue so when I turned the breaker back on I expected the RCD to trip but it stayed on. I tried switching everything off and back on one by one but nothing tripped the RCD.

I discovered that if all the CBs are on the RCD will turn on sometimes but trip when turning on other times. By that I mean repeatedly turning it on until it stays on.

Dos this this sound like a faulty RCD? I am going to buy one to rule this out.

Could it be any other issue?

Thanks in advance for the help

No it doesn't sound like a faulty RCD, it sounds like you have an intermittent fault possibly on an appliance or the circuit/heating system.

I highly advise that you don't keep on repeatedly Resetting the RCD until it stays on and get an electrician to come have a look and carry out some tests.

 

[ipf]

RCD doing it's job, by the looks. Try living in the cold for a while.

 

[Des 56]

Does this this sound like a faulty RCD?
No it sounds like a system or appliance fault




I am going to buy one to rule this out.
You are going to buy one and probably waste money that could be used to finance the services of an electrician and his test meters

 

[Engineer54]

Where's your earth leakage clamp, or don't you own one??

 

[Ciaran Lang]

I'm an electrical fitter to trade but it was industrial work. (although I'm now an office based electrical designer in the oil and gas industry) So I can do certain domestic work without an issue. I wouldn't go poking around things I know nothing about, especially electricity.

if it's an intermittent fault with something would it be advisable to turn everything off and then leave one thing on eg turn off the heating, cooker etc and leave on the fridge/freezer for a while to see if it trips? I can only imagine being a kitchen appliance as it was only the WiFi router and the telephone that was plugged in elsewhere in the house.

The RCD tripping made me think it was a serious fault but I couldn't understand why it would switch on sometimes but not other times. The only explanation I could come to was a faulty RCD.

I just want to get a grasp of the issue before calling out an electrician.

Thanks again.

 

[Leesparkykent]

If your an electrician, you should be more than aware how an RCD works and what would cause it to trip.

 

[Knobhead]

As an electrical fitter you should at least know the basics. I do know what your job entails and electrical theory doesn’t play a great role.

As an electrical fitter I assume you work for a company, you wouldn’t get far as a freelancer in such a specialised branch of the trade. The company must employ some electricians, why haven’t you asked them?

 

[ChristianG]

Keep everything unplugged including extension leads. Hopefully your boiler is on a fused spur. If it still trips, then turn the boiler off via a fuse spur (hopefully) then the RCD should reset. It sounds like a possible fault with the boiler. Is the boiler on a timed setting? If it is put it on constant and see if it trips. Bare in mind that you really to need to not be tight and just splash out on an experienced electrician. Oh if they walk in with just a screwdriver, tell them to go and get their test gear.

to be honest it could be so many different things, I,ve had a wedding photo picture that's been up for 10 years, then the RCD has started to trip and we found 240v at the picture hook, not in my house btw.

 

[Spoon]

If you don't have a earth leakage clamp meter then the best thing you can do mate is get an electrician in.
Or if you want to find out more about the fault then get your hands on one and do a bit of testing of the circuits and appliances on them.

 

[Octopus]

Kitchen with heating on the circuit - tripping at irregular times. my moneys on the fridge or central heating...

 

[Marvo]

The problem with intermittent RCD tripping faults is it's often the cumulative result of more than one earth leakage fault. If you don't have a megger tester and an earth leakage clamp meter this kinda fault will run you round in circles.

 

[Ciaran Lang]

I know how RCDs operate etc but I have just never came across this problem before.

I'm not an electrician, a common mistake my family and friends make when they have issues with their electrics! And I am also working in an office now doing electrical design, we have "engineers" that I hadn't spoke to as yet as it only reoccurred last night.
I have no issue getting a good electrician out to have a look but I would rather be able to pinpoint the cause to a certain appliance(s)

Since this happened last night when no one was in, I can only imagine it being the central heating (which is timed and had turned off about half an hour before I came home and the house was warm), fridge or washing machine as no other appliance would've been on.
All the appliances in the kitchen except the washing machine are on a fused spur. With these off, the RCD reset but I then turned everything back on and it never tripped. If as you guys suggest it is an appliance intermittent fault I may just need to wait it out and see under what conditions it trips again. I'll go with unplugging the washing machine for now and see if it trips.

Unfortunately I don't have a megger or earth leakage clamp.

Thanks for help. It's much appreciated!

 

[Deleted member 9648]

The problem with intermittent RCD tripping faults is it's often the cumulative result of more than one earth leakage fault. If you don't have a megger tester and an earth leakage clamp meter this kinda fault will run you round in circles.

I cant believe that once again nobody has mentioned an IR test(until post #13)

 

[Engineer54]

I cant believe that once again nobody has mentioned an IR test(until post #13)

Know what you mean, but in this case, it wouldn't have mattered much if it had been mentioned earlier, as the OP doesn't have ANY test equipment!!

 

[LEO]

Hi there Ciaran,

I've experienced these types of faults quite a few times, some decent info above in the previous posts and ideally a IR tester and a earth leakage clamp tester are needed here. You can do your own process of elimination and may get lucky and find what the culprit is, if it is down to one item? Could be quite likely that it is down to more than one item though and a cumulative effect of earth leakage across the circuits protected by the RCD, this is more difficult to diagnose and simply unplugging items won't prove what item is at fault. You could have say 8 items connected for example all producing 3mA of earth leakage, the RCD is just about holding, and everything is fine, then your central heating kicks in at 4pm and your RCD trips, your central heating may have 7mA of earth leakage, the combined amount exceeding the RCD rating and then trips, this doesn't necessary mean the central heating is at fault.

Also when you are switching fused spurs off, if they are not D.P, take into consideration that the neutral is still connected and you could quite easily have a couple of volts or so floating on the neutral, if the earth leakage/fault is on the neutral side of things then this could cause the RCD to trip to(could be a P-E fault or N-E fault or both), even though you have ruled that item out because you have the fused spur switched off. Same goes for plugged in items to sockets, always unplug from the socket not just flick the switch off as you could be in the same scenario if they are not D.P, you could easily end up chasing your tail then and going round in circles. Depending on the nature/origin of this fault they can be time consuming to narrow down. Take into account any supplies to outside, pond pumps, garden shed etc etc that may be connected unknowingly to one of these RCD protected circuits.

Goodluck.

 

[Marvo]

.......You can do your own process of elimination and may get lucky and find what the culprit is, if it is down to one item? Could be quite likely that it is down to more than one item though and a cumulative effect of earth leakage across the circuits protected by the RCD, this is more difficult to diagnose and simply unplugging items won't prove what item is at fault.

This is the problem with no test equipment. Many household items have an acceptable amount of background leakage which isn't a fault because, to a point, the earth is functional as well as protective. If you have a faulty appliance with twenty-odd mA of leakage and you unplug a PC or maybe a Playstation that has a few mA of functional leakage via surge arrestors and the RCD will hang in even though the fault hasn't been eliminated.

Finding RCD tripping faults by elimination is basically guesswork and as I previously said can run you around in circles and may even have you spending money replacing or repairing items that aren't actually at fault.

Beg, borrow, kidnap or steal a megger tester and an earth leakage clamp.

 

[Knobhead]

Beg, borrow, kidnap or steal a megger tester and an earth leakage clamp.

Would you lend someone with no training your test gear?

He would better getting one of the guys he works with to sort the job out.

 

[walsh builders]

Testing equipment alone will not find your problem, you need someone to operate it.

There's no way on this earth that you could guess what the fault is. Take the money that you were willing to spend on an RCD and give it to an electrician. That seems the most sensible (and safe) solution

 

[LankyWill]

Why does he need an earth leakage clamp? Wouldn't a megger suffice, surely an IR test would find it? What's the benefits of using an earth clamp meter? I might buy one if its worth it.

 

[Deleted member 9648]

Why does he need an earth leakage clamp? Wouldn't a megger suffice, surely an IR test would find it? What's the benefits of using an earth clamp meter? I might buy one if its worth it.

He doesn't need an earth leakage clamp.
This discussion was had on a similar thread after E54 stated he cant understand how anyone can manage without one these days. Well I've never had one and can think of only a handfull of situations in 35 years where an RCD tripping problem could not be found quickly with just an IR test. I consider that earth leakage is nearly always due to a low IR.
The only reason I can think of where an IR test may not be the answer is where cumulative leakage from IT equipment etc was causing RCD tripping. In this instance a ramp test of the RCD with and without load would give an indication of the leakage anyway.If for example the RCD ramped at 28ma no load and 10ma on load the leakage would be 18ma.

 

[Marvo]

You sometimes get variations in test results between indirectly calculated leakage by using a megger tester and actual real-life leakage measured using an earth leakage clamp meter this is particularly the case with electronic items and IT equipment and even lighting drivers and ballasts.

I'm not advocating that a clamp tester is better or worse than an IR tester, I'm just saying there's certain test scenarios where it's likely to be more accurate and there's a couple of reasons I would defend the use of one particularly when testing appliances or circuits that have appliances connected. Firstly it's direct measurement rather than indirect so you actually seeing the fault current that's causing the tripping. Secondly you're seeing the fault current under normal AC power-on conditions rather that taking an off-line measurement using a DC test signal.

 

[Deleted member 9648]

You sometimes get variations in test results between indirectly calculated leakage by using a megger tester and actual real-life leakage measured using an earth leakage clamp meter this is particularly the case with electronic items and IT equipment and even lighting drivers and ballasts.

I'm not advocating that a clamp tester is better or worse than an IR tester, I'm just saying there's certain test scenarios where it's likely to be more accurate and there's a couple of reasons I would defend the use of one particularly when testing appliances or circuits that have appliances connected. Firstly it's direct measurement rather than indirect so you actually seeing the fault current that's causing the tripping. Secondly you're seeing the fault current under normal AC power-on conditions rather that taking an off-line measurement using a DC test signal.

I would not disagree with that at all. I have no doubt that an earth leakage clamp would be a useful addition to fault finding.However I confess that it constantly surprises me that as soon as an RCD tripping thread comes up the advise is always 'ramp test the RCD' or earth leakage clamp.For me the the first test is an IR test,it's been that way for 35 yrs and probably wont change now!

 

[Octopus]

Why does he need an earth leakage clamp? Wouldn't a megger suffice, surely an IR test would find it? What's the benefits of using an earth clamp meter? I might buy one if its worth it.

I can't believe that a spark can work without an earth clamp meter these days. One of my pre checks before I quote for a cu change is to check the earth leakage.

 

[Knobhead]

Where do you check for E/L?

 

[Octopus]

Where do you check for E/L?

Initially on the tails if accessible. Then the main earth.

 

[Knobhead]

Initially on the tails if accessible. Then the main earth.

It wasn’t a trick question.

Other than the odd domestic job E/L hasn’t really been a bother to me. I can only think of four LV main circuits that had E/L trips on the breakers, the relays had been disabled many years ago.
I tried to get one working, that was a mistake. I couldn’t get it to hold at 2.5% FLC. (800A FLC=20A leakage to trip.) I kept upping the threshold, I gave up at 5%.

OK the tails is the only place you’ll get a true reading, it’s the same as the core balance transformers used in the systems above.

 

[Engineer54]

He doesn't need an earth leakage clamp.
This discussion was had on a similar thread after E54 stated he cant understand how anyone can manage without one these days. Well I've never had one and can think of only a handfull of situations in 35 years where an RCD tripping problem could not be found quickly with just an IR test. I consider that earth leakage is nearly always due to a low IR.
The only reason I can think of where an IR test may not be the answer is where cumulative leakage from IT equipment etc was causing RCD tripping. In this instance a ramp test of the RCD with and without load would give an indication of the leakage anyway.If for example the RCD ramped at 28ma no load and 10ma on load the leakage would be 18ma.

And as i remember, i gave you sound reasons WHY today's electricians need to have a leakage clamp meter in test kit.... An MFT IR test and ramp test, can be next to useless in tracing some leakage faults and at best be a long drawn out affair. I'll unequivocally stand by my statement that all electricians these days should own a leakage clamp as part of their test equipment!!

 

[Deleted member 9648]

And as i remember, i gave you sound reasons WHY today's electricians need to have a leakage clamp meter in test kit.... An MFT IR test and ramp test, can be next to useless in tracing some leakage faults and at best be a long drawn out affair. I'll unequivocally stand by my statement that all electricians these days should own a leakage clamp as part of their test equipment!!

Fair enough,I'll happily accept that some consider it essential. Not for me though,Just about every week I'll be dealing with an RCD tripping issue,and they rarely take long to sort out with just my IR tester and an RCD tester. Come the day when there's one I cant sort out and somebody comes in with an earth leakage clamp and does what I couldnt do then maybe I'll go out and buy one. But till then.....

 

[Octopus]

Fair enough,I'll happily accept that some consider it essential. Not for me though,Just about every week I'll be dealing with an RCD tripping issue,and they rarely take long to sort out with just my IR tester and an RCD tester. Come the day when there's one I cant sort out and somebody comes in with an earth leakage clamp and does what I couldnt do then maybe I'll go out and buy one. But till then.....

Well...... consider this senario...

Occassional tripping of RCD - over a period of weeks, nothing consistent except same RCD.

Using ECM, establish that the circuits on this RCD have about 18-20mA combined, and adding items on the 2 socket circuits would occassionally make it trip!
Turn off all MCB's
Record readings for all circuits

Yup - all have some leakage

Moved "worst" circuit onto a RCBO as its a Hi-Int CU

No repeat of tripping since Sept '14

All over in just over 1 hour!

This to me justifies the expense of the ECM!

 

[Deleted member 9648]

Well...... consider this senario...

Occassional tripping of RCD - over a period of weeks, nothing consistent except same RCD.

Using ECM, establish that the circuits on this RCD have about 18-20mA combined, and adding items on the 2 socket circuits would occassionally make it trip!
Turn off all MCB's
Record readings for all circuits

Yup - all have some leakage

Moved "worst" circuit onto a RCBO as its a Hi-Int CU

No repeat of tripping since Sept '14

All over in just over 1 hour!

This to me justifies the expense of the ECM!

Like I said,if I get an instance where I cant sort out an RCD tripping issue with an IR tester and RCD tester I'll consider an ELCM.It hasnt happened yet.
Out of interest did you IR test before using the clamp?

 

[Octopus]

Like I said,if I get an instance where I cant sort out an RCD tripping issue with an IR tester and RCD tester I'll consider an ELCM.It hasnt happened yet.
Out of interest did you IR test before using the clamp?

Yup. Clean good figures - can't remember exact results but nothing low enough to worry about

 

[PEG]

Like I said,if I get an instance where I cant sort out an RCD tripping issue with an IR tester and RCD tester I'll consider an ELCM.It hasnt happened yet.
Out of interest did you IR test before using the clamp?

I presume it is the fixed installation you are IR testing,and ramp testing with loads connected.

I think the ease at which leakage can be assessed with a ELCM,switching combinations of loads,justifies the ownership,of what is these days,a reasonable expense on equipment.

As in the example Murdoch quoted,i have done a similar series of tests,regarding an issue with a Bio-filter plant,added to RFC of a property,where the many separate loads on the system,were only causing problems during the instance of a "perfect storm" of chance,when all operated simultaneously.

I know mine has proved its' worth enough not to be without one in the future. :icon12:

 

[Marvo]

.....I think the ease at which leakage can be assessed with a ELCM,switching combinations of loads,justifies the ownership,of what is these days,a reasonable expense on equipment.

Another reason is the high hold feature, you can clamp it on a circuit and run an appliance for several minutes and record the max leakage during the time.

I'm sure you could get by without one if you really wanted to and you have a megger tester and RCD ramp tester but there are some occasions when they're the best tester for the job at hand and like you say, for the price of them nowadays, I can't see any reason not to carry one as standard equipment.

 

[Jaxo]

Well...... consider this senario...

Occassional tripping of RCD - over a period of weeks, nothing consistent except same RCD.

Using ECM, establish that the circuits on this RCD have about 18-20mA combined, and adding items on the 2 socket circuits would occassionally make it trip!
Turn off all MCB's
Record readings for all circuits

Yup - all have some leakage

Moved "worst" circuit onto a RCBO as its a Hi-Int CU

No repeat of tripping since Sept '14

All over in just over 1 hour!

This to me justifies the expense of the ECM!

I was in the IR & RCD test camp and thought the earth leakage clamp meter would be of no use..... Until I read this. Makes perfect sense mate.. Will be my next tool purchase

In saying that, I haven't been beat yet.... But in a few occasions I've spent a lot of time fault finding

Going to an intermittent Red tripping issue in the morning... Nice start to the week :-/

 

[Deleted member 9648]

I will consider an ELCM following the input above,but old habits die hard lol.

 

[DPG]

What's a reasonably priced model that people would recommend? Something with decent accuracy on low readings. Daz

 

[Octopus]

What's a reasonably priced model that people would recommend? Something with decent accuracy on low readings. Daz

I bought a really good unit - the Metrel MD 9270 - which wasn't cheap BUT does lots of things - so I had saved up to buy it and a mate had one!

 

[shanky887614]

And as i remember, i gave you sound reasons WHY today's electricians need to have a leakage clamp meter in test kit.... An MFT IR test and ramp test, can be next to useless in tracing some leakage faults and at best be a long drawn out affair. I'll unequivocally stand by my statement that all electricians these days should own a leakage clamp as part of their test equipment!!

+1 why start disconnecting circuits and ir testing each one?

you shouldnt ir test the circuit with apliances plugged in anyway.

i would bet money that its probably the fridge or another appliance, its a lot easier to clamp the earth and then turn the breakers off to find where the most leakage is coming from and then go from there

 

[shanky887614]

I bought a really good unit - the Metrel MD 9270 - which wasn't cheap BUT does lots of things - so I had saved up to buy it and a mate had one!

What's a reasonably priced model that people would recommend? Something with decent accuracy on low readings. Daz

Another reason is the high hold feature, you can clamp it on a circuit and run an appliance for several minutes and record the max leakage during the time.

I'm sure you could get by without one if you really wanted to and you have a megger tester and RCD ramp tester but there are some occasions when they're the best tester for the job at hand and like you say, for the price of them nowadays, I can't see any reason not to carry one as standard equipment.

you can get a good one for £50 and they will soon pay for themselfs, test-meter stock them.

 

[richard1972]

do you use IR test majority of time and only use ELCM on intermittent tripping ? or is it quicker to use ELCM on permanent tripped rcd sometimes ? i want to buy ELCM but trying to understand how often i will use versus how much to spend

 

[Engineer54]

you can get a good one for £50 and they will soon pay for themselfs, test-meter stock them.

Only in your dreams!! 120-150 Quid is more like it!!

EDIT... just checked test-meter and they do the TEM for around a hundred notes, which if i were after a budget ELC, would be the unit i'd be looking to purchase!!

 

[Richo77]

Any one purchased the TEK 775 meter? They are about £70. Thinking of getting one. Are they any good?

 

[Engineer54]

Any one purchased the TEK 775 meter? They are about £70. Thinking of getting one. Are they any good?

You really need a higher resolution than that provided by the TEK775...

 

[Richo77]

Ok cheers E54

 

[telectrix]

Fair enough,I'll happily accept that some consider it essential. Not for me though,Just about every week I'll be dealing with an RCD tripping issue,and they rarely take long to sort out with just my IR tester and an RCD tester. Come the day when there's one I cant sort out and somebody comes in with an earth leakage clamp and does what I couldnt do then maybe I'll go out and buy one. But till then.....

funny enough, on a new install i have an intermittent RCD tripping. nothing plugged in. IR tests L-N >299Meg. L-E >299Meg, N-E >299Meg. ramp test 27mA. trip times normal @ 31mSec @ x1 and 11mSec @ x5.

 

[Deleted member 9648]

+1 why start disconnecting circuits and ir testing each one?

you shouldnt ir test the circuit with apliances plugged in anyway.

i would bet money that its probably the fridge or another appliance, its a lot easier to clamp the earth and then turn the breakers off to find where the most leakage is coming from and then go from there

I think it's clear from the replies from respected members that an ELCM is a useful addition to fault finding.I would dispute that it is essential based on the fact that I dont possess one and yet successfully rectify RCD tripping problems regularly week in week out in little time.
Why shouldnt you IR test a circuit with appliances plugged in? If I'm fault finding I want everything in place so that the fault is there when I test. Initially I unplug known sensitive equipment but leave everything else in place and do a 'soft' 250v test to begin with. It's rare that a 250v test wont show up an IR issue that a 500v test would,but if necessary I'll do a 500v test after double checking that there is no sensitive equipment connected.
I've also lost count of the times I've been called to intermittent tripping problems where another electrician has 'fixed' it only for the issue to continue. On nearly every occasion an IR test has identified a fault that the other electrician would have found if he'd IR tested correctly.
It's clear to me from the inumerable threads on this subject that the advise is always 'ramp or clamp'.
Even if I buy a clamp I'll still IR test before considering anything else.

 

[Octopus]

I think it's clear from the replies from respected members that an ELCM is a useful addition to fault finding.I would dispute that it is essential based on the fact that I dont possess one and yet successfully rectify RCD tripping problems regularly week in week out in little time.
Why shouldnt you IR test a circuit with appliances plugged in? If I'm fault finding I want everything in place so that the fault is there when I test. Initially I unplug known sensitive equipment but leave everything else in place and do a 'soft' 250v test to begin with. It's rare that a 250v test wont show up an IR issue that a 500v test would,but if necessary I'll do a 500v test after double checking that there is no sensitive equipment connected.
I've also lost count of the times I've been called to intermittent tripping problems where another electrician has 'fixed' it only for the issue to continue. On nearly every occasion an IR test has identified a fault that the other electrician would have found if he'd IR tested correctly.
It's clear to me from the inumerable threads on this subject that the advise is always 'ramp or clamp'.
Even if I buy a clamp I'll still IR test before considering anything else.

Really?

I test the RCD to check its functionality, then the clamp to check the "back ground" leakage, then IR - unless its abundantly clear one specific circuit is to fault!

 

[davesparks]

+1 why start disconnecting circuits and ir testing each one?

you shouldnt ir test the circuit with apliances plugged in anyway.

i would bet money that its probably the fridge or another appliance, its a lot easier to clamp the earth and then turn the breakers off to find where the most leakage is coming from and then go from there

You should clamp round the tails as a group not the earthing conductor, otherwise the result will be affected by the bonding and small currents which can circulate in the earth.