UK RCD Anomalies FYI

[Ohmless]

Hi folks.
I don't normally enter information on forums but here goes, in case it helps someone.
Two RCD peculiarities solved:
1) RCD tripping randomly + Solar panels Feed in Tariff.
After all usual checks and many frustration weeks eventually deduced tripping mostly coincided with dawn and dusk particularly. Solution was to run solar feed-in through its own mini (RCD) consumer unit. Yay!
2) Garage/workshop Consumer Unit RCD tripped (and tripped main CU. RCD) but the garage RCD would not reset. Carried out all the usual checks (these can be found on numerous helpful threads) to no avail. Contrary, however, to many listings that advise that RCDs rarely go wrong, and one professional site advising that if the RCD won't go back on then the fault is definitely within the circuit (s) 'because a RCD is at fault only if it doesn't trip' - yes, the RCD was at fault and it was that which actually tripped the main CU RCD! Replaced the offending item and Bingo! - And there were no faults on any of the garage circuits...
..ho hum, so put them all back together again

 

[Mikegh]

RCDs are totally imperfect devices but they may save your life or the building

Go figure

 

[pc1966]

They can and do fail. Though failing in a not-tripping mode is worse than becoming a tad premature and few test them periodically and, as above, the RCD might just save you on day, It if works.

 

[UNG]

I've had quite a few that failed the testing when brand new and fresh out of the box

 

[LastManOnline]

I've had quite a few that failed the testing when brand new o and was and fresh out of the box

When talking about failed rcd, s or any other electrical accessories, it's worth noting the brand used. I have consistently used either Hagar or GE throughout my career. Can't remember a single issue with either brand. Due to circumstances I needed to use Garo and experienced so many issues I wrote to the supplier and now avoid them like the plague. If we go for price over quality there will naturally be a "price" to pay

 

[Lucien Nunes]

the RCD was at fault and it was that which actually tripped the main CU RCD

It's interesting to ponder how the garage RCD (which presumably only connects to L & N) could cause a current imbalance to trip the main RCD regardless of what faults it might have.

My only suggestion is that downstream of it there are some loads with significant suppression capacitors that can cause a trip if the neutral of a DP switch opens before the line, and in this situation the garage RCD was merely playing the part of a DP switch. If so, the main RCD might still trip occasionally when the new RCD is operated manually.

 

[MJPD29]

When talking about failed rcd, s or any other electrical accessories, it's worth noting the brand used. I have consistently used either Hagar or GE throughout my career. Can't remember a single issue with either brand. Due to circumstances I needed to use Garo and experienced so many issues I wrote to the supplier and now avoid them like the plague. If we go for price over quality there will naturally be a "price" to pay

You get what you pay for. There's no doubt about that. Some cheaper brands like BG have caused me a right pain in the past. At least 3 faulty RCDs by them that I can remember, only ever supplied one BG board and had a faulty RCD, and then a faulty replacement. The others were supplied supplied me by customers to fit. Avoid cheap brands like the plague.

 

[UNG]

When talking about failed rcd, s or any other electrical accessories, it's worth noting the brand used. I have consistently used either Hagar or GE throughout my career. Can't remember a single issue with either brand. Due to circumstances I needed to use Garo and experienced so many issues I wrote to the supplier and now avoid them like the plague. If we go for price over quality there will naturally be a "price" to pay

I don't think brand matters a lot of the problems I've had wouldn't necessarily be found under normal testing as suggested in BS7671 , how many ever ramp test an RCD as it is not one of the prescribed tests how many would think to do it. I only started ramp testing RCD's on every job after going back to do some additional work on a job I had completed 6 month's earlier came to the testing and the RCD results were a little different to what I got 6 months earlier ended up ramp testing and the RCD was only tripping at around 36mA, so was it faulty at install or had it become faulty, since then I've found a number of faulty RCD's that will pass all the tests except for the ramp test

 

[LastManOnline]

My only suggestion is that downstream of it there are some loads with significant suppression capacitors that can cause a trip if the neutral of a DP switch opens before the line,.....

That's an interesting point. I, m curious to know what the circuit would look like if the N does open before time.? In my mind the leakage to earth from the Line from the downstream rcd should, nt necessarily be greater than it was prior to the rcd opening? (when been used as DP switch)

 

[LastManOnline]

I don't think brand matters a lot of the problems I've had wouldn't necessarily be found under normal testing as suggested in BS7671

I would disagree on this point. When I complained to the manufacturer, they sent their rep with a "present", a selection of rcbo, s, rcd, s and mcb, s, which was very hard to say no to. However the results in practice were the same.Failure rate compared to their better quality competitors was rediculous

, how many ever ramp test an RCD as it is not one of the prescribed tests how many would think to do it.

No its not proscribed, but ramp testing is becoming increasingly more common

I only started ramp testing RCD's on every job after going back to do some additional work on a job I had completed 6 month's earlier came to the testing and the RCD results were a little different to what I got 6 months earlier ended up ramp testing and the RCD was only tripping at around 36mA, so was it faulty at install or had it become faulty, since then I've found a number of faulty RCD's that will pass all the tests except for the ramp test

I agree on this point. An rcd tested today can vary quite a bit in 6 months when tested again. This is common to all brands in my experience. But is has more to do with the rcd mechanism which needs regular use to stay "fit" I think an rcd should really be tested every month to keep it in good nick.

 

[LastManOnline]

RCDs are totally imperfect devices but they may save your life or the building

Go figure

The rcd, for reasons I have never fully understood has not been valued in the UK as it has in most other countries. Though that is clearly changing. Its a crucial accessory in the "Electrical family".

Also rcd, s subject to testing in ways other accessories are not. They are tested to death. Its, easy to establish when they fail and hence much easier to be critical of them. We have currently no such means of testing mcb, s or fuses. We install them purely on trust. We cannot know how many issues may have been caused in the past due to them malfunctioning.

 

[pc1966]

The rcd, for reasons I have never fully understood has not been valued in the UK as it has in most other countries. Though that is clearly changing. Its a crucial accessory in the "Electrical family".

I think historically the use of polarised plugs with a reliable earth (both plug design and the RFC) and a fairly strict regime for design Zs to clear on the OCPD in the UK meant they were not seen as so important for indoors stuff (other than TT supplies) compared to a lot of the EU or USA where neither was always true.

Where they did come in to popularity was for outdoor sockets / extension leads as there was quite a long period from the 70s through to 00s when folk were killed in the garden following a mower or hedge trimmer encounter with its supply cable. Far less common now as most sockets are on RCD supplies now, and the trend for battery tools as well.

Of course we have also seen tragedies with cable damage in homes leading to wider adoption in the regs (e.g. for lights as well) along with the aspect of cables < 50mm from surfaces or walls with internal metalwork.

 

[Mikegh]

Started off as supplementary protection when using portable appliances


Moving now to all 30ma rcbo protected final circuits

So many issues and quirks with them though, blinding, standing leakage , ramp, stiction,nuisance trips

 

[UNG]

The rcd, for reasons I have never fully understood has not been valued in the UK as it has in most other countries. Though that is clearly changing. Its a crucial accessory in the "Electrical family".

I think we better understand their limitations and failure points better than other countries sparks from what I've seen and even talking to sparks in other countries they don't test them and some look quite surprised when you tell them test equipment is available to check trip times and trip current as if it is some sort of alien procedure
Do I totally trust RCD's to operate when really needed and my answer would be no but they are a good backup to good circuit design

 

[Mikegh]

I think we better understand their limitations and failure points better than other countries sparks from what I've seen and even talking to sparks in other countries they don't test them and some look quite surprised when you tell them test equipment is available to check trip times and trip current as if it is some sort of alien procedure
Do I totally trust RCD's to operate when really needed and my answer would be no but they are a good backup to good circuit design

Surprised to hear other countries don't test

An RCD test result is only really a snapshot like an MOT

It might pass.on the day of testing but could fail another day

Hager for me is probably the brand Ive found to be the most reliable