Random RCD Tripping

[bernardgreen]

this is called "exercising" and could loosen things up that have been sitting there doing nothing for 5 years.

Rubbish, You would be adding to the wear and tear of the mechanism and thus shortening it's life span.

 

[Risteard]

Well, it's going to prove the RCD is satisfactory

The standard tests prove that. The actual tripping current is irrelevant. All it needs to do to satisfy the requirements is not trip at half the rated residual operating current; operate within 300mS for BS EN types (200mS for older BS types) at I delta n, and within 40mS at 5 I delta n.

 

[Risteard]

That is sometimes appropriate, but it addresses a problem which is the opposite of what the OP is experiencing.

I don't agree that it's appropriate. The RCD should be regarded as failed if it doesn't trip in the required time. Exercising it to create a false pass is certainly not the correct course of action.

 

[EFLImpudence]

Well, it's going to prove the RCD is satisfactory

The standard tests prove that.

I don't understand what you mean.
Was I not advocating the standard tests?

The actual tripping current is irrelevant.

I would have thought that was the only relevant thing in such a case as this.
So, a ramp test would not be included in what you call the standard tests. I would do it even though it is not required for an EIC.

If it trips at 16mA then it is more likely to trip more often, or if it does trip at ½IΔn, maybe it trips at 5mA, then it is unsatisfactory.
This must be possible otherwise it would not be one of the tests.

With RCD tripping being complained of by a customer, would you not check the RCD first?

All it needs to do to satisfy the requirements is not trip at half the rated residual operating current; operate within 300mS for BS EN types (200mS for older BS types) at I delta n, and within 40mS at 5 I delta n.

Yes, we all know that but only one of those is relevant to the problem in this case.

 

[Risteard]

If it trips at 16mA then it is more likely to trip more often, or if it does trip at ½IΔn, maybe it trips at 5mA, then it is unsatisfactory.

16mA is acceptable for a 30mA RCD. So it is within tolerance.

If it trips at 1/2 I delta n then it fails - this is a standard test.

A ramp test doesn't add to this as the standard tests prove that it is operating correctly.

 

[EFLImpudence]

Still not sure what your original point was or why it is different than what I wrote.

 

[Seb101]

So I'm resurrecting this thread because 8 months later I was still no closer to knowing what it is, but I now have a potential clue. Since I last posted about this in May 2019 it's tripped a handful of times, sometimes months apart, sometimes days apart.

Today, it tripped twice within a couple of hours, which was annoying but also gave me a possible clue.

When it was happening fairly regularly last year I purchased a UPS for my computer, router and modem. The UPS is a 'line interactive' style one which as well as providing battery backup for the appliances, it also actively monitors the mains supply and is able to correct over and under voltage situations. When it detects an under-voltage (which is set to a threshold of 220V) it switches to the battery powered inverter to bring the output back up to ~240V.

Earlier tonight, a while before the first RCD trip, the UPS alarmed for under-voltage, when I checked it the mains input voltage was all over the place, dropping as low as 213V and up to 235V. The UPS alarmed for this another 2 times, then the RCD tripped about 20 minutes after that. I then reset the RCD, and the UPS alarmed for under-voltage again a few minutes later, then a few minutes after that the RCD tripped again.

So annecdotally at least, it would seem that under-voltage on the main supply could be tripping the RCD. I did a bit of reading on this and the conclusion is that voltage drops on their own cannot trip an RCD however rapid fluctations in supply voltage are indicative of HV switching changes in the network which can cause noise on the supply which can trip an RCD. So I am concluding that this is probably the case, and perhaps I have a particularly sensitive RCD.

Case closed.

 

[oldbutnotdead]

Interesting- and worth an email probably to your electricity supplier in the first instance since the low number is outside tolerance for UK electrical supply. They'll probably swerve and point you at the DNO for your area but could be an amusing hobby if you wanted one. Does the UPS app give you a pretty graph- if so then screenshot it & attach it to the email

 

[Seb101]

Interesting- and worth an email probably to your electricity supplier in the first instance since the low number is outside tolerance for UK electrical supply. They'll probably swerve and point you at the DNO for your area but could be an amusing hobby if you wanted one. Does the UPS app give you a pretty graph- if so then screenshot it & attach it to the email

I would imagine there is some threshold for 'transient' dips/spikes on the network, especially when dealing with the aftermath of a storm. Either way, I don't have the time or inclination to get into a correspondence battle with the DNO

 

[oldbutnotdead]

I would imagine there is some threshold for 'transient' dips/spikes on the network, especailly when dealing with the aftermath of a storm. Either way, I don't have the time or inclination to get into a correspondence battle with the DNO

Ah yes, valid point (Storm Thing has been a bit of a non-event here, an excess of surface water but otherwise nowt to write home about)

 

[evdamadiynot]

I've had random tripping on two occasions over the years
One ,some 20 years ago was cured by tightening an earth post screw on a metal ceiling lamp.This only tripped when there was heavy pedestrian traffic above.
The other more recently was cured by moving an (aledgedly)IP junction box from a laid down to upright position.It actually turned out to be a gland without a grommet and was only a problem in a rain bearing north easterly wind.
Going through Absolutely every possibility is a time consuming pita but it paid off for me......