RCD tripping on mains outage.

NewClareman

Hi,

hoping for some practical advice...

We moved to a rural area with power glitches about once a month. It can last anything from a few seconds to minutes. When the power goes it often trips the RCD on the switchboard, which means no power to the sockets when it returns. The RCD trips on mains interruption even when all that is connected is a new fridge and freezer. A local electrician tested the installation and could find no fault. He has offered to change the RCD, to see if it is faulty.

I'm wondering whether anyone has come across a situation like this and how the solved it. Im also wondering whether the protection devices have changed in the 15 years since the house was built and, if so, whether they are likely to be more resilient than older devices? I don't want to get the RCD changed just for the sake of it. At the same time we have now lost two freezers of food, when power failed while we were away.

Any thoughts welcome.

kirk.

On the freezers anyway they're allowed to be wired without RCD protection afaik but would mean some rewiring.

There's always a risk anyway with an RCD and freezers as the RCD can trip on a fault

Probably test the outgoing side of RCD anyhow for faults and try swopping RCD at a guess .

Also you could fit a separate RCBO for freezer circuit that might fix your freezer problem.

NewClareman

Yeah, I had thought of wiring a separate circuit for the freezer, as it happens there's an easy route from the fuse board. In previous times I'd have run this myself, but now I'd get a RECI. If all else fails that's what I'll do, as we're regularly away, from spring onwards.

However, I'd still lose remote access to cameras, lights and heating and the heating itself, so not ideal.

I'd really like to get to the bottom of this but I no longer have access to test equipment - hence my post here. I suspect there may be power surges from heavy duty farming equipment, but I've no way of checking.

kirk.

If you're away I would talk to the rec about wiring it without RCD protection

If you're away a lot the RCD can trip anyway on a fault even without that power loss problem you're having

JL spark

Did your electrician do a ramp test to see what the RCD was actually tripping at ? Leakage wise

meercat

Agree with Jl spark

the rcd needs to be tested

I have come across instances where the rcd won’t reset under load and the mcbs needs to be off for the rcd to reset. I’d suspect this is what’s happening in your case. It should be easy to replicate this by turning your main switch off and back on again.

my advice is to replace the rcd and(as others have said) install a dedicated line for your freezer

NewClareman

The RCD was not tested AFAIK - I wasn't standing over his shoulder. The electrician told me he did an insulation test on the wiring and verified the earthing was ok.

The RCD resets under load, I've checked this many times. I've also used a clamp meter to check for leakage, which is negligible. The issue appears to be directly related to the quality of the mains - I've been in the house when the mains was briefly interrupted and the RCD tripped, likewise for mains outages.

Anyway,, I'll get the RCD replaced, as suggested; and the freezer on a dedicated circuit.

10-10-20

This is probably a grey-area in the RCD's behaviour spec. It's trying to watch the deltas between Live and Neutral during a period where the incoming power is falling. The programmed behaviour might be overly cautious and drops the load as a precaution. You might find that another RCD manufacturer has a different behaviour in this respect. But nowhere in any RCD spec-sheet have I ever seen this documented.

kirk.

Think maybe I've seen something similar, like you're saying I think it's some sort of temporary imbalance when power is lost causing the trip

Other issue for the op is he's rural and having outages , he might need to get surge protection fitted as a precaution

10-10-20

https://www.boards.ie/discussion/comment/119938974#Comment_119938974

Yeah, falling voltages means that the mechanical device for latching the RCD can lose power and drop the breaker. Some of the newer RCD's are circuit based rather than mechanical and have a programmed response to dropping voltages, rather than a mechanical movement.

https://youtu.be/4HQ7XOVNabg?t=413

NewClareman

Thanks guys, that's exactly the type of response I was hoping for. I don't believe for a second that the existing RCD is faulty but the scenario you outline above sounds very plausible. I can't think of any other one. Before going away I unplugged everything but the fridge and freezer, both of which are new. The immersion and cookers/hob were isolated at their switches as were the showers. It still tripped, on a power outage. at other times it has worked for a number of months, without issue.

I don't see any real advantage in replacing the current unit with a random unit that the electrician has handy. How common are circuit-based RCD's and how can they be identified? I'm prepared to source one myself, if necessary. If this works I'll also add one to the circuit for the freezer.

I too had wondered whether surge protection would be of any benefit. I'm not too worried about lightening, as the final feed to the house is underground. However I suppose it could provide some protection against power surges. It's a road I'd rather avoid, if possible. For maximum effectiveness the earthing requirements are pretty onerous, and not so easy to implement.

10-10-20

Schneider super-immunised (Si) types might fit that bill.

https://www.se.com/nz/en/faqs/FA299180/

https://www.se.com/ww/en/product/download-pdf/A9R91225

kirk.

https://www.boards.ie/discussion/comment/119940401#Comment_119940401

RCDs vary a lot it's the obvious thing to do swop it out for a new one and see if that fixes it assuming everythings been tested

And why would you want to fit a new RCD on the freezer when you said rewiring was straightforward

NewClareman

Unless the RCD is a different design from the one fitted there is a good chance that a swap will achieve nothing. If I had no other option I'd go down that route. I'd now prefer to source the suggested RCD and hopefully get it sorted in one go. (Before the new regs I'd have just swapped it out myself. I'm competent to do the work but not a member of RECI.)

I don't like leaving the freezer without protection, hence why I'd fit a dedicated RCD for this and the fridge. I'm going to get the RECI to do this anyway, as I think it's good practice.

kirk.

It's the food you want to protect not the freezer

NewClareman

Yes, I want to protect the food - but not at the expense of electrical safety. Protection devices are intended to prevent accidents, and even death. In my opinion the revised standards could go even further in relation to fitting RCDs to fixed devices such as hobs and ovens.

Yeah, I know that much more relaxed guidelines have been in place, and still are in many countries. However, the technology is now available to do better; and should be used.

kirk.

Disagree but I'll leave it there

Bruthal.

Yes. Saving people from something that's not really killing them.

NewClareman

https://www.boards.ie/discussion/comment/119946026#Comment_119946026

I'm not sure what your point is, electrocution in any domestic setting in Ireland is extremely rare. However, even one death is too much, if it is easily preventable.

Bruthal.

My point is, or opinion at least, that you are identifying a risk with a fridge that probably is zero practical risk.

In the case here, if it was my own setup, id split the circuits onto a second rcd or several rcbos, or try the swop, or dedicated circuit, depending on whether the trip happens when switching the main switch off?

Where did you test for phase/neutral imbalance/residual current?

NewClareman

In my previous house I installed separate RCDs for the shower, fridge/freezer, lights and external socket in the boiler house. With a young family, I erred on the side of caution. Might seem excessive but my sister in law's husband was electrocuted, when I was a teenager. It was not his fault, there were multiple installation failures by professionals; at a house where he was working. He left behind a widow and a young family.

I measured for phase neutral imbalance at each individual circuit, under load, with all loads on other circuits removed. I also checked for earth leakage on each individual circuit and at bonding to exposed metalwork. Maybe my methodology was flawed and I'm open to suggestions - I'm retired, so plenty time on my hands. :)

The RCD only trips when there is a mains outage, even if this is momentarily. Even then it doesn't always trip. I would love to move to multiple RCBO's, as you suggest. However, getting an electrician to do this, at reasonable cost, is unlikely in the current climate.

Bruthal.

The best way to check for imbalance is clamp at phase and then neutral at the meter location if possible. And compare the readings.

Is the installation neutralized? It might reduce the chance of it happening if it is.

Another thing to look at is testing all rcd neutrals to earth with everything plugged out. It is one of those often hard to solve ones though, even if a swop of rcd stops it happening.