RCDs trip after isolation?

[dkjfnvfd]

Last week I checked a workshop that had a beeping dekstop UPS and found it was in discharge mode and all the 30 mA RCDs built into the small power sockets had tripped. Not all of the sockets had anything connected to them.

I absent mindedly reset them all and left it at that, but over the weekend I thought about it again and decided it was pretty weird.

I don't know for sure but I think the RCDs probably tripped either after a recent isolation of the workshop, or after the power was reinstated.

I've had a think on my own and asked a couple of people at work and none of us thing an RCD should have tripped in these situations, but when I've informed the relevant people they haven't responded which has left me wondering if it's not a problem.

Should I be concerned or should I let it drop?

 

[itsmoked]

RCDs can get faked out and trip due to spurious happenings. This can happen with unusual loads.

Computer switching power supplies often have capacitors between lines and the ground for EMI reduction requirements. These caps are 'leakage' that RCDs see and it goes towards the available leakage budget that the RDC will trip at. I'd reset as you have and keep an eye on the situation. If you get another RCD trip in less than a year you'll need to take further action. The first of which would be replace your existing RCD device with a new one of different make. Often RCDs can be too sensitive due to manufacturing tolerances or just flat bad. Replacement often cures nuisance tripping.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I have seen inverters with a "modified sine wave", a polite term for a two step square wave trip downstream GFCI (RCD) receptacles with no load. Daisy chaining standard receptacles downstream of the GFCI receptacles made the situation worse.
eg: A single GFCI receptacle may hold in at no load, but adding downstream non GFCI receptacles would cause a no-load trip. The length of the downstream circuit seemed to be a factor.
With four rising and four falling square wave-fronts per cycle, strange things may happen with sensitive circuits. It may be high frequency harmonics coupling with the equipment grounding conductor and a resulting HF current to ground.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RRaghunath]

I have seen the RCDs maloperating when there is overvoltage in the distribution company lines due to a transient fault (overvoltage in unfaulted phases in case of SLG fault) or single phasing.
If the circuits are RCDs are stable after resetting, it could be due to the above.