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

 

[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