Voltage sags tripping RCD

[beddhist]

We live in the rice paddies and recently our RCD keeps tripping, usually accompanied by V sags and/or spikes. (lights flicker and the UPS relay clicks on and off.) PEA is aware of the problem and they are upgrading mains lines everywhere as I am writing this. (My guess as to the cause are the many bore pumps being installed everywhere to compensate for the lack of irrigation water.)

But why does that trip the RCD? We have a separate switch board with RCD in the workshop and I had to adjust this to the lowest sensitivity and it hasn't tripped since. In the house it's not adjustable. Sometimes the RCD will refuse to even switch back on or trip again soon.

Should I replace the RCD for something better?

[bankruatsteve]

1 hour ago, beddhist said:

Should I replace the RCD for something better?

No.  (except for possible difference in brand quality, there is nothing "better")

Low voltage should not affect RCD.  Neither should high voltage unless it puts downstream equipment into a fault condition somehow. 

The main reason for RCD trip is critters (ants, geckos, ants) getting into outlets or equipment boards, relays, etc.  Then, when things get really humid, faults go through the nests, eggs, whatever.  Check outlets for that.  Check AC compressors for ant invasion.  You should find the culprit(s) eventually.

edit:  I have even found dust webs creating faults in very humid conditions.

Edited March 15, 2021 by bankruatsteve

[Crossy]

Yes ^^^.

Plus, I'd put up with it until PEA stop mucking around and see if things improve.

Then (when it doesn't improve) and you've checked for critters.

I would look at replacing your single RCBO/RCD with a simple MCB and then placing individual RCBO's on "hazardous" circuits, water heaters, bathroom outlets, outdoor outlets, kitchen outlets (but keep the freezer on its own non RCD circuit), outdoor lighting and leaving other less risky circuits just on MCBs.

Do you have a lot of technology, PC's, inverter A/C etc etc? Most of these devices leak quite considerably to earth as part of their design. So these could be putting your RCD already on the point of tripping, noise or a mains glitch could tip it over the edge. Unfortunately checking for this type of thing needs some specialist kit (low current range AC clamp meter) not the sort of thing that finds a lot of use in the average toolbox.

[beddhist]

Thanks guys! There is definitely a connection between sags and tripping. I can see the voltage drop on my solar inverters and the lights often flicker. I can see how critters can do it and I have vacuumed a few spiders out of sockets.

PCs leak current by design? Seems daft... But yes, I do have a few of these and once, when I was unable to reset the RCD we unplugged everything and the moment I plugged the UPS back in it tripped. Then it worked again only minutes later.

Ok, we will wait for the works to be completed, but at current speed that will take weeks, if not months.

[Crossy]

15 minutes ago, beddhist said:

PCs leak current by design? Seems daft...

It's the RFI filters on the inlets (anything with a switching power supply has them), intended to stop nasty interference getting out into the wide world (not the other way round as many think).

It's the same circuit that makes desktop PCs tingle if you run them without an earth.

It's also worth understanding that RCDs have a pretty large "grey area" in their characteristics to take account of manufacturing tolerance.

For a 30mA RCD:-

• < 15mA : Device must NOT trip.
• >= 30mA : Device MUST trip.
• 16-29mA : Device MAY (or MAY NOT) trip.

[beddhist]

interestingly, I never had this problem in NZ and I ran more old PCs there (also out in the countryside). Never heard of anybody else having it, either. When we lived in our workshop here we had none of this equipment and the RCD still tripped, until dialled back.

[bankruatsteve]

Humidity and dust webs. Give your PCs a vac.