RCD problems

[securespark]

Thanks. That'll make an interesting read (yes, I'm sad....).

 

[Murdochcat]

It’s no different to designing circuits limited to 10 mA IIRC

that’s why dual or single rcd boards shouldn’t be installed these days

 

[ebee]

I came from an age where RCDs were the "New kids on the block" and became either in their own encloser example for one circuit only use and wired directly after the MCB (or fuse) then a bit later they were built in as the consumer unit DP on/off switch protecting all circuits, no such thing in common as dual etc., we have come a long way in these few short years.
ELCBs were getting more common before this time and you had a choice of Voltage or Current operated , both were popular but less so than the bog standard pure plain DP switch as you only main isolator , off current ELCBs were later named as RCDs and Voltage ones ceased to be an item of choice.

yes there was a time (a very long time) before RCDs etc and a few of us on here will remember them.

I am still a front ender - well they were quite new when I put them in!

 

[ericmark]

It was on my return to the UK from the Falklands when I came across widespread use of RCD's, this would have been around 1990, and from the outset the problem was lack of neutral switching. So an item not being used could cause the RCD to trip. I had thought we would move to double pole switching, and to an extent with class II that has happened, But the RCBO has resulted in the "Every installation shall be divided into circuits, as necessary, to: (iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation" actually happening, splitting an insulation into two circuits has never been really acceptable since 2008.

The problem however is, although the regulations are not retrospective, where there has been a clarification rather than a change, that clearly shows we have in the past made errors in reading the regulations, so those faults need rectifying.

I am sure we have all made errors, I bought a new board and RCBO's and read on the packets type B, I was a little pleasantly surprised, type A would have been fine, only after they were fitted did I realise miss labelled and in fact type AC curve B. I feel the RCD is secondary protection, so as such type AC is better than no RCD, but it was not an electrical error, it was an English error.

So if inspected 9-8-2021 the question is should the way the circuits are arranged raise a comment? The IET dropped code 4 (does not comply with current BS 7671 requirements) as being unhelpful and confusing for the recipient. And we really only code dangerous and potentially dangerous so could be given a code C3, but one can hardly complain if the use of single RCD was not reported as something which would be a good idea to redress, not so much a danger, but an inconvenience.

I look at the "(viii) Limiting the number of circuits connected to any one RCD to three." and the first problem with that is to define a circuit. We have "Circuit. An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)." however, one can't have a circuit from a final circuit, that simple English, but a FCU on a ring final, supplying an array of sockets is really a circuit from a final circuit, and if that rule arrived in the UK some would simply combine circuits. So one for garage, one for sockets and microwave, and one for hob and oven, and it now complies with Australia/New Zealand standards, so would not help.

The problem is to explain to a homeowner why they should fit all RCBO's, or a SPD, or any other device takes time, it should be the owner who decides, but he can only decide if he knows all the pros and cons, and if not explained, then be it fit RCBO's or leave the common market the man in the street is likely to make the wrong selection.

So to correct in this case, £250 for parts, and a day's wages to correct, that is not chicken feed, to do less, then the problem will likely return, I would not like the task of explaining why when it says all good unto 2031, we are now saying he needs major work doing, LEGRAND TENBY 30mA type B RCBO's, 16A 606418 & 32A 606420 £49.99 as obsolete stock, so cheaper to swap whole consumer unit. Also out of stock for 32 amp and they are type AC.

I had even as an electrician in 2019 consider if a twin RCD consumer unit was worth the risk, not for very long, just lost £300 of food when RCD is last house tripped while we were away, but we are looking at a lot of money, to charge, I was fitting new, as it was clear the old Wylex fuse box was not a valid option, I needed new, and an extra £100 to ensure it did not cause more waste food was nothing. But I would not be happy having to update, which seems a modern board.

 

[Harry Bloomfield]

Which so far as the OP is concerned, means (s)he likely has an accumulation of small leakages, and the best fix is to replace the single RCD, with RCBO's. Just replacing the MCB, with the highest leakage, might well be enough, to prevent the nuisance tripping, but they would need to determine which circuit that is.

 

[ebee]

I must admit, the use of dual RCD boards is better if using double pole switching MCBs rather than purely single pole switching and solid N link type MCBs, one make I am aware of is the Garo type but personally I prefer an all RCBO consumer unit for what little extra it costs these days (well in a TN system at least)

 

[FrodoOne]

When did this rule come in?

As far as I know, since RCDs were introduced into Australia.

For a rather "earthy" discussion of this,
See

from 2:20.
[Referencing: AS/NZS3000:2018 2.6.3.2.3.3 (b) ]

However, he then found that he had "missed-out" on 2.6.2.4.(b)
See from 3:10

I have a copy of AS/NZS 3000:2007
and
the requirements of 2.6.2.4 (a & b) were the same then.

 

[ericmark]

I think their rules are good, we also say, although not in any rule book, background leakage should not exceed 30%, where I think we fail, is we don't ask the inspector to record the background leakage. We have to write down the insulation resistance, it seems, so we can see when an installation is degrading, but that will only work if the inspector is given previous test results, but we have never recorded background leakage, if we did then we could see at a glance if due to some degrading or simply due to capacitive and inductive linking.

As to more than one RCD, there are clearly problems with that, a caravan/boat supply will likely have two RCD's in series, not parallel, however with true caravans and boats we also have a 12 or 24 volt supply as well, it is the "mobile home" which causes the problem, and with this case, the way the supply is split.

Clearly pre-2008 install, so we only needed to have sockets likely to be used outside back then protected, but even post 2008, there are no rules to say anything like each floor socket outlets should be protected by two or more RCD's, and they should be arranged, so failure of a socket RCD should not result in loss of light, or any other installation design feature which would reduce the danger should an RCD trip. And I can't see how one could, my flat only have one socket circuit, which is enough, the house is spilt side to side, so should a socket supply fail I can use an extension lead to get a supply without it running up/downstairs, but there are no rules to say do this, just common sense.

I have in the last week abandoned the idea of putting the central heating supply on RCD protection, in the interests of personal safety, yes decided safer not to have RCD protection, than to have in the winter months to descend to my flat to reset any RCD down external steps in snow or ice, the risk of a fall due to snow or ice is far higher than the risk of a shock due to an earth fault.

I did some years back have an extension lead with a section of outer insulation removed so I could used my clamp meter to see what items used, it has since been replaced with one of these in fact also have two which connect to internet as well, however having an extension lead were one can get the clamp around line and neutral (the lives) without the earth, would seem a good idea to test leakage of items like the dishwasher, and washing machine.

But still back to same question, what can @heliarch do to aleave the situation? I think the meter I got at £35 is about the cheapest to read in 1 mA incruments. I got the

as both 1 mA incruments and DC, maybe there is a cheaper AC only option, but price does seem to have gone up. My orignal meter on the left only measured in 10 mA incruments, and that does seem to be the norm. It still works and measures frequancy so did not get the version of meter to right which could do that. But the other option was the same price and one needs to ask is it even worth measuring? He has a problem, showing what the problem is, does not cure it.

 

[Harry Bloomfield]

As to more than one RCD, there are clearly problems with that, a caravan/boat supply will likely have two RCD's in series, not parallel, however with true caravans and boats we also have a 12 or 24 volt supply as well, it is the "mobile home" which causes the problem, and with this case, the way the supply is split.

A hang-over from when you could never be certain a site supply actually included an RCD, or one in working order.

I was reminded I have an RCD fitted many years ago, as the one time only RCD in the place, protecting the garage/workshop/hut/summerhouse, and outdoor sockets. I was testing out something still plugged in, turned off, and managed to get the neutral to earth. It took both the local RCD out, as well as the RCD in my consumer unit.

My caravan is plugged into one of the outdoor sockets, and so has three RCD's supplying it, in series.

 

[ebee]

"As to more than one RCD, there are clearly problems with that, a caravan/boat supply will likely have two RCD's in series, not parallel, however with true caravans and boats we also have a 12 or 24 volt supply as well, it is the "mobile home" which causes the problem, and with this case, the way the supply is split."

I reckon that in this case it has two possible benefits.
1/ If one RCD fails then you have got the other that might work.
2/ The RCD inside the caravan/boat with not protect against the external commando plug and flex damage, the other one will, if in working order.