Tripping ELCB?

[ericmark]

Unless one's name is eric

I did test the RCD and the insulation resistance, it was only the leakage I failed to test.

 

[JohnW2]

I did test the RCD and the insulation resistance, it was only the leakage I failed to test.

If the RCD has tested satisfactorily and does not trip with the circuit loaded, that will at least give you an upper bound for the possible 'earth leakage', even if you haven't measured it.

I suppose that if you could measure the earth leakage reasonably accurately (and that might not be easy) it might alert you to a situation in which the 'background leakage' in a circuit was fairly close to the trip threshold of the RCD.

 

[ericmark]

When I lived in that house, the clamp-on I had measured in 10 mA increments, so I suppose could have had 9 mA leakage. The insulation resistance was many MΩ, but that tests with DC.

 

[Murdochcat]

Indeed. Many people's first thought seems to be to blame the device, although that very rarely is the reason - even if it is one of those 'nuisance RCD trips' which some of us seem to suffer (and which, again, are very rarely due to a faulty RCD).

Not sure I agree with this.

Older RCD's (and some brand new ones) are prone to becoming more sensitive and therefore trip well below 22mA - hence why ramp testing RCD's is the first thing to do

 

[ericmark]

Older RCD's (and some brand new ones) are prone to becoming more sensitive and therefore trip well below 22mA - hence why ramp testing RCD's is the first thing to do

I must admit, early days I would test the RCD with the MCBs turned off, I now realise the problem with that, however not sure on the way around the problem.

The problem is DC and high frequency either inhibiting the tripping or reverse. Also, the problem of strain on the terminals affecting the performance. So the RCD/RCBO needs testing without touching the terminal screws, clearly a new RCD would be tested when manufactured, so we are looking for something which has happened when installed, be it strain, DC or high frequency, so MCB's need to be on.

We can measure back-ground leakage, so if leaking 2 mA we want it to trip at less than 28 mA, hence need to ramp test, the 15 mA and 30 mA tests can't allow for back-ground leakage, but also we can't measure the tripping time with a ramp test, I note the testing required has reduced, as has setting tester to type AC, A, F, or B. And each tester is slightly different. I am sure the ramp test on my tester is a few stages, not analogue, think in 3 mA stages, but not sure.

I have tried measuring DC leakage, in theory my clamp-on will measure DC in 1 mA increments, but on the DC range it needs to be zeroed, and the slightest movement can change the reading, so would be happy not got 1 amp DC, but as to 6 mA DC, I would not trust my meter to be that accurate.

As to high frequency, which is more likely a problem, as tripping when it should not trip, without an oscilloscope can't really test, hence why we need to test when circuits connected. So I often use the 13 amp lead to test, simply plug in and press the button. Remember, we are not filling in a test sheet, we are looking for a problem.

So big question, can these

cause a problem with RCDs? It seems they put a high frequency signal superimposed on the mains, so would expect these would need a type F RCD, and not seen any in real life.

So how do we test for high frequency upsetting the RCD other than testing the RCD with everything running, which is clearly not what we do when commissioning a new installation.

 

[Harry Bloomfield]

So big question, can these

cause a problem with RCDs? It seems they put a high frequency signal superimposed on the mains, so would expect these would need a type F RCD, and not seen any in real life.

I have some of those, and no - they cause my RCD's no issues that I am aware of.

 

[ericmark]

Good to know, type AC or type A, wonder if it varies make to make?

 

[JohnW2]

When I lived in that house, the clamp-on I had measured in 10 mA increments, so I suppose could have had 9 mA leakage.

With a display showing 2 decimal places (of amps), a reading of "0.01 A" could, if perfectly accurate, obviously (just by 'rounding') be indicating a current anything between 5 mA and 14.9999 mA. Any current less than 5 mA would display as "0.00 A" and any current between 15 mA and 24.999 mA would display as "0.02 A".

However, taking the example of the ('yellow') 2 dp meter you recently showed us, that had a claimed accuracy of 1.5% + 4digits. If I understand correctly (maybe not!) that would seem to mean that a displayed reading of "0.01 A" could arise with a current anything between zero and about 44.9999 mA

... which, if true, would render it totally useless for the task

 

[JohnW2]

Not sure I agree with this. Older RCD's (and some brand new ones) are prone to becoming more sensitive and therefore trip well below 22mA - hence why ramp testing RCD's is the first thing to do

I don't doubt that that sometimes happens, but I think that 'drift' of the trip threshold in the other direction ('up') is far more common, isn't it - not the least due to 'stiction', particularly if RCDs are not 'exercised' (by testing) fairly regularly!

On the face of it, I don't find it easy to think of a likely mechanism for a shift in the direction you suggest.

In any even, I still stick with the view I expressed - that 'unexplained' ('nuisance') RCD trips are only rarely due to the RCD being 'out of spec', since when such issues are investigated by testing the RCD, it is nearly always found tobe 'within spec'. Don't forget that even a brand new "30 mA" RCD is 'allowed' to trip at a residual current of about 15 mA.

 

[Murdochcat]

I don't doubt that that sometimes happens, but I think that 'drift' of the trip threshold in the other direction ('up') is far more common, isn't it - not the least due to 'stiction', particularly if RCDs are not 'exercised' (by testing) fairly regularly!

On the face of it, I don't find it easy to think of a likely mechanism for a shift in the direction you suggest.

In any even, I still stick with the view I expressed - that 'unexplained' ('nuisance') RCD trips are only rarely due to the RCD being 'out of spec', since when such issues are investigated by testing the RCD, it is nearly always found tobe 'within spec'. Don't forget that even a brand new "30 mA" RCD is 'allowed' to trip at a residual current of about 15 mA.

Many years at the coal face trumps DIY opinions

 

[JohnW2]

Many years at the coal face trumps DIY opinions

Hardly a helpful comment .... what exactly do those many years at the coal face indicate?

 

[SUNRAY]

Many years at the coal face trumps DIY opinions

Hmmmm....

Many years using a pick and shovel versus 60+ years of precision electronic/electrical experience...

However I've dealt dealt with hundreds, if not thousands, of RCDs and RCBOs and I think it's fair to say the number which have any issues I can count on my hands and that includes the versions with disconnected functional earths.

 

[Harry Bloomfield]

I don't doubt that that sometimes happens, but I think that 'drift' of the trip threshold in the other direction ('up') is far more common, isn't it - not the least due to 'stiction', particularly if RCDs are not 'exercised' (by testing) fairly regularly!

I wouldn't really expect much stiction, because both RCD's, RCBO's, and MCB's are well 'wound up' mechanically, by the process of switching them on.

 

[JohnW2]

Many years using a pick and shovel versus 60+ years of precision electronic/electrical experience...

I do sometimes wonder what on earth he was doing during all his years at the coal face (whilst you, and even I, were testing many RCDs!).

However I've dealt dealt with hundreds, if not thousands, of RCDs and RCBOs and I think it's fair to say the number which have any issues I can count on my hands and that includes the versions with disconnected functional earths.

Certainly not thousands for me, but probably at least a hundred or two, and my experience has been the same as yours - and, as I implied, of the few I have found to be 'out-of-spec, nearly all have had too high a trip threshold.

 

[JohnW2]

I wouldn't really expect much stiction, because both RCD's, RCBO's, and MCB's are well 'wound up' mechanically, by the process of switching them on.

Maybe, but if they were last 'switched on' 10 years ago (and, yes, even I have seen some of them), there will have been a faiir amount of opportunity for 'stiction' to set in