Author Topic: RCD Nuisance tripping  (Read 1196 times)

RCD Nuisance tripping
« on: December 02, 2020, 04:23:28 pm »
We're having big problems with nuisance trips with the consumer unit here.

It's nearly always associated with turning on something that draws a lot of power - shower, cooker (oven or induction hob) and occasionally the kettle.

I've just read that nuisance tripping can be made worse by having surge protectors on things like PCs or socket blocks. Anyone with any experience/comments on this?

I've just petulantly ordered a UPS for the office as my work PCs are getting as pissed off with this as me.

Feanor

  • It's mostly downhill from here.
Re: RCD Nuisance tripping
« Reply #1 on: December 02, 2020, 04:41:20 pm »
Yes, I had such issues.

The idiot who replaced our Consumer Unit when we were having building work done years ago installed a single whole-house RCD which was forever tripping.
A 30mA RCD can trip at 18mA.
That's not a lot in a big house with lots of electronics and electrical tat.

How many RCDs are there?
If it's a split load CU with two RCDs, it may be possible to re-jig the load and residual leakage between the two.

In my case, I had a lot of computer equipment in one room, so I used a big 240:240 isolating transformer and ran all the IT kit through that.
The RCD doesn't 'see' the leakage on the other side of the transformer.
That reduced the nuisance tripping a fair bit.

In the end, I replaced the consumer unit with one stuffed with RCBOs.
These are individual circuit breakers with their own RCD; ie every individual circuit has it's own RCD.
So I've got 30mA per circuit to play with.

No nuisance tripping now, but it was quite expensive.


Re: RCD Nuisance tripping
« Reply #2 on: December 02, 2020, 05:03:46 pm »
We had similar years ago with the campsite. The only thing to reduce the frequency was to put in trips with a higher trip current. It was one trip for about eight vans. Not ideal.

Ultimate fix was indeed to provide each pitch with its own RCD protected circuit.

Rust never sleeps

Re: RCD Nuisance tripping
« Reply #3 on: December 02, 2020, 05:04:41 pm »
I was rather hoping that this thread might have been heralding a new Fat Boy Slim release.
Rust never sleeps

Kim

  • Timelord
Re: RCD Nuisance tripping
« Reply #4 on: December 02, 2020, 05:47:51 pm »
If you had a safe way to measure the current in the earth conductor of a load (eg. a short extension lead with a mains-rated ammeter on the earth), you could go around sniffing for excessive leakage.

It might just be the cumulative effect of lots of electronics - most DC power supplies normally leak a little to earth by nature of their design.  In which case your only reasonable[1] option is not to have it all on the one RCD.

Circuit breakers (of all kinds) tend to get trippier as they wear, so it might just be a little oversensitive to surge current.

Happiness is a Schneider RCBO board.


[1] Discounting industrial RCDs with adjustable trip, isolation transformers and the like.
Careful, Kim. Your sarcasm's showing...

Feanor

  • It's mostly downhill from here.
Re: RCD Nuisance tripping
« Reply #5 on: December 02, 2020, 05:54:57 pm »
Using a 100mA RCD is not compliant with the domestic Wiring Regulations.
It needs to be 30mA.

Kim

  • Timelord
Re: RCD Nuisance tripping
« Reply #6 on: December 02, 2020, 05:55:59 pm »
Using a 100mA RCD is not compliant with the domestic Wiring Regulations.
It needs to be 30mA.

Rightly so, IMHO.
Careful, Kim. Your sarcasm's showing...

Feanor

  • It's mostly downhill from here.
Re: RCD Nuisance tripping
« Reply #7 on: December 02, 2020, 06:06:34 pm »
Happiness is a Schneider RCBO board.

Here's a photo of what I installed at Feanor Towers to solve the issue:


IMG_20151121_222120[1] by Ron Lowe, on Flickr

RCBOs are not cheap, though.

Re: RCD Nuisance tripping
« Reply #8 on: December 02, 2020, 06:21:25 pm »
I'd start by assuming you have an actual fault somewhere (either wiring or appliance) that's being pushed over the edge by switching things on and off. Which means some experimentation to see if isolating a particular circuit makes the problem go away.

RCDs are the difference between electrocution being often fatal to being mostly harmless. I certainly wouldn't do anything to fuck with their effectiveness.

Tim Hall

  • Victoria is my queen
Re: RCD Nuisance tripping
« Reply #9 on: December 02, 2020, 06:27:25 pm »
I was rather hoping that this thread might have been heralding a new Fat Boy Slim release.
C'mon we gotta kick that gangster shit current leak
C'mon we gotta kick that gangster shit current leak
C'mon we gotta kick that gangster shit current leak
There are two ways you can get exercise out of a bicycle: you can
"overhaul" it, or you can ride it.  (Jerome K Jerome)

Re: RCD Nuisance tripping
« Reply #10 on: December 02, 2020, 06:28:14 pm »
They do start "nuisance tripping" when they age/get worn and so it may require replacing the RCD unit.  If you can find one to fit...

When ours went - it got to the point where it refused to hold in when switched back on I had to have the whole consumer unit replaced as the RCDs were no longer available to fit it.  The new unit now has twin RCDs splitting the load so that only half the house goes off when one trips which is a much better idea.

Re: RCD Nuisance tripping
« Reply #11 on: December 02, 2020, 07:01:06 pm »
Thanks for the input so far, folks.

Any solution is somewhat complicated by this being a rental house - and there's definitely some dubious wiring in the loft; but that's a lighting circuit that has nothing to do with the fact that it's the ring-mains that get tripped, lights stay on. The landlord has been pretty responsive to issues so far, so I guess I'll fit the UPS in the office to protect The Money, and start sending emails to the landlord.

Kim's idea for protecting the Pi-of-Awesomeness (DNS, DHCP) with a power-pack was a life saver (thanks Kim!) as *nothing* works if that goes down; even if the router doesn't start after a trip, we still have local networking.

It's inconvenient as much as anything. I can't risk turning the power-shower on if fboab's on a Zwift race, and everything has to be turned off if we want to start the oven.

Re: RCD Nuisance tripping
« Reply #12 on: December 02, 2020, 08:04:20 pm »
Just for the LOLs, two weeks ago I needed to replace a double 13amp socket which Mum had b0rked by dropping a table light onto it and smashing it to bits.
I couldn't isolate it using any of the RCDs
I ended up switching off the current to the entire house.
It would appear that some of the upstairs 13amp sockets are fed by the downstairs 5amp lighting circuit. ::-)
That'll be why the hoover cooked a fuse when used upstairs.
Nice one, Dad.

Adam

  • It'll soon be summer
    • Charity ride Durness to Dover 18-25th June 2011
Re: RCD Nuisance tripping
« Reply #13 on: December 02, 2020, 08:25:28 pm »
In my old house, when I had it re-wired about 20 years ago, almost straight away I found that the consumer unit was very sensitive so that any time an old style filament bulb blew, it would trip. 

Solved by switching to LEDs so no more bulbs to go.  I remember around that time Argos were selling 10 LEDs for £1 as part of some promotion to persuade people to save energy and switch to LEDs.  I've still got some of those LEDs unused in a box somewhere.
“Life is like riding a bicycle. To keep your balance you must keep moving.” -Albert Einstein

Feanor

  • It's mostly downhill from here.
Re: RCD Nuisance tripping
« Reply #14 on: December 02, 2020, 09:52:40 pm »
In my old house, when I had it re-wired about 20 years ago, almost straight away I found that the consumer unit was very sensitive so that any time an old style filament bulb blew, it would trip. 

Solved by switching to LEDs so no more bulbs to go.  I remember around that time Argos were selling 10 LEDs for £1 as part of some promotion to persuade people to save energy and switch to LEDs.  I've still got some of those LEDs unused in a box somewhere.

That's normal; an incandescent lamp going pop will often trip an MCB.
Not a fault.
Modern MCBs are very sensitive devices compares to wire fuses, and mostly for the better.

They can trip on 2 different criteria:
1) Magnetic: This will respond very quickly to high instantaneous surges like when a lamp pops.
2) Thermal: A slower-acting thing that will trip after a sustained but small over-current.

In both cases, they are superior to wired fuses.

Re: RCD Nuisance tripping
« Reply #15 on: December 02, 2020, 10:21:18 pm »
As has been said up thread,  a compotent electrician can test the RCD, using the correct test equipment to get a readout of performance, and also get fixed equipment cooker/shower tested for leakage. That is part of full inspection and testing, which is now a five yearly requirement on a rental property.
https://www.gov.uk/government/publications/electrical-safety-standards-in-the-private-rented-sector-guidance-for-landlords-tenants-and-local-authorities/guide-for-landlords-electrical-safety-standards-in-the-private-rented-sector

fboab

  • It's a fecking serious business, riding a bike
Re: RCD Nuisance tripping
« Reply #16 on: December 02, 2020, 10:28:37 pm »


I can't risk turning the power-shower on if fboab's on a Zwift race, and everything has to be turned off if we want to start the oven.
I'm glad to know we have our priorities correct.
TSS is not Total Sex Score, Chris!

Kim

  • Timelord
Re: RCD Nuisance tripping
« Reply #17 on: December 02, 2020, 10:29:59 pm »
As has been said upthread, first get a compotent electrician to test the RCD, using the correct test equipment to get a readout of performance, and also get fixed equipment cooker/shower tested for leakage. That will lead onto full inspection and testing, which is now a five yearly requirement on a rental property.
https://www.gov.uk/government/publications/electrical-safety-standards-in-the-private-rented-sector-guidance-for-landlords-tenants-and-local-authorities/guide-for-landlords-electrical-safety-standards-in-the-private-rented-sector

I believe that requirement begins in April.

We're waiting for an electrician to get back to us with a date for an EICR.  Uncertain how pedantic they're likely to be re: access to every socket.  (And whether they'll be arsed to wear a mask, like the gas man didn't.)  Are we going to have to play Sokoban with the fridge so we can pull out the washing machine?  Are all the books going to have to come off the shelves, etc...

OTOH, if they persuade the landlord to upgrade the CU to something with an RCD on the upstairs ring, that'll be a win.
Careful, Kim. Your sarcasm's showing...

Re: RCD Nuisance tripping
« Reply #18 on: December 04, 2020, 07:35:41 pm »
It is indeed a single RCD for the whole house (sockets only though).

UPS arrived today, so let's see if that makes any difference other than just to my peace of mind.

TBF we have a f*cktonne of electrical kit in the place - I have four PCs in my office alone, and then there's a room full of trainer/tv/pc kit upstairs. Oh and a PS4 and various other things in the living room; nearly all of it on surge-protected socket extensions, so there's likely a not-insignificant amount of leakage already - so when we turn on something that pulls a lot of current, maybe that's enough to tip a aging RCD over the edge?

TimC

  • Old blerk sometimes onabike.
Re: RCD Nuisance tripping
« Reply #19 on: December 05, 2020, 05:09:46 am »
In my old house, when I had it re-wired about 20 years ago, almost straight away I found that the consumer unit was very sensitive so that any time an old style filament bulb blew, it would trip. 

Solved by switching to LEDs so no more bulbs to go.  I remember around that time Argos were selling 10 LEDs for £1 as part of some promotion to persuade people to save energy and switch to LEDs.  I've still got some of those LEDs unused in a box somewhere.

I had an LED bulb go last night, which tripped the whole house RCD and which, while the bulb was in its socket, would not allow a reset. It did not trip the lighting circuit it was on. This was at about 3am, so it took a bit of diagnosis with a tired brain!

Re: RCD Nuisance tripping
« Reply #20 on: December 06, 2020, 01:17:09 pm »
We had the old style fuse box ripped out of this house when we moved in almost a decade ago (having a kitchen wall ripped out and total renovation of that area meant getting a sparky in). That meant that we suffered trips when bulbs blow, but luckily the sparky wired the West and East wings onto separate main breakers splitting the house vertically rather than horizontally; that way we still have light and power on half of each floor when the trip goes.
MrsH's kiln does the normal kiln thing of causing trips if it's not been used for a while, as they absorb moisture and RCDs are very sensitive to that.