Is the designer to blame? Should people claim? RCD trips.

[JohnW2]

Hi John. All good here thank yo. Hope all is well with you and yours.

We're fine, thanks, and I'm pleased to hear that you are, too. Grandchild No. 2 is scheduled to arrive in a week or two's time, but goodness knows when we will first be able to see her 'in the flesh'!

I meant the logic of the thread. I fit 5 sockets and there is a trip due to the equipment used. I don't see how I would be expected to sort this at my expense. I just wonder if Eric thinks I should replace a socket if the customer overloads it, or trips over a lead. I don't have the gift of precognition.

Thanks for clarifying. Yes, as I hope is clear from my various responses, I think eric is worrying about, and talking about addressing, an issue which normally can't be addressed. As I've said, in some cases (e.g. a room full of IT equipment), the designer will know that the total leakage current will be high, such that splitting across more than one circuit/RCD would be necessary - but in nearly all other situations, there's nothing much that a designer without a crystal ball can do about the perceived 'potential problem'.

I suppose that, in a world in which equipment with significant earth leakage is becoming increasingly prevalent, there might come to be a case for re-considering the number (and placement) of outlets that one should have on a sockets circuit - but I doubt that we have got to a stage at which that's yet really necessary. ... and, again, what is sensible will always be crucially dependent on the actual situation in question.

Kind Regards, John

 

[ericmark]

Back to basic with two up, two down no real question two RCD's are enough, and in a hotel with 20 bedrooms two RCD's are not enough, and some where between the two extremes there has to be a point where two RCD's are on their limit, so talking about an existing premises where a designer comes in and charges an existing distribution box, for a consumer unit, and after the change the RCD's are regular tripping, at what point is the client responsible for correcting, and at what point is the designer responsible for the correction?

So this house, 5 bedrooms, three floors, two kitchens, two bathrooms, plus shower room, two living rooms, and a dinning room, so not small, but not a hotel, my house all RCBO, next door just two RCD's similar size house, and they trip on regular basis, mine don't, so should the guy who changed the consumer unit now replace it with a all RCBO version labour free, I will not say material free as clearly had it been all RCBO to start with then it would have cost more from materials, but the designer has to my mind got it wrong, had the house had three RCD's then on the balance, but to my mind it is unlikely with just two RCD's that house would ever get away without a regular trip.

But where is the point where one can say down to designer, and where is it down to user, and this is the problem, there is no line as far as I can see where you can say designer was at fault.

 

[scousespark]

Following your logic an electrician can’t win. We don’t know why any RCD trips. If there is a fault in the circuit, the electrician should fix it. If is due to an appliance, or actions taken by the customer, there is no come back on the electrician. I will chat with the customer and take best effort to elicit faults. There is only so far any of us can go to protect circuits from leakage. Just as we can’t prevent overloading sockets, or running a lead across a room. As we move to a standard of RCBO for all circuits, the impact of leakage should reduce.

 

[JohnW2]

... 5 bedrooms, three floors, two kitchens, two bathrooms, plus shower room, two living rooms, and a dinning room, so not small, but not a hotel... just two RCD's ... and they trip on regular basis, mine don't, so should the guy who changed the consumer unit now replace it with a all RCBO version labour free ... the designer has to my mind got it wrong ... where is the point where one can say down to designer, and where is it down to user, and this is the problem, there is no line as far as I can see where you can say designer was at fault.

I'm not sure that it is particularly helpful or appropriate to talk about 'responsibility' or 'blame' - and particularly inappropriate to blame a designer who had absolute no control over how an installation would be used. ...

If you really want to look at it 'legally', then I think a Court would probably only say the designer was 'to blame' (i.e. 'negligent') if it could be established that 'no reasonable designer' (or perhaps 'no substantial body of reasonable designers') would design an installation for such a house which only had two RCDs - and I really don't think that is the case. Indeed, other than in very large homes (or, of course, all-RCBO installations), I would think it would actually be pretty unusual for domestic installations to be designed with more than two rcds, even for 'moderate-sized homes' such as you describe.

Kind Regards, John

 

[EFLImpudence]

Aren't two separate lots of regulations being confused?

Ones for premises where high CPC current is expected and high-integrity earthing should be installed, and

ones for dwellings where it is not.

 

[JohnW2]

As we move to a standard of RCBO for all circuits, the impact of leakage should reduce.

One would hope so, at least a bit - and the impact of a trip, if/when it happened, would then obviously be much less widespread.

having said that, I would suspect that in most domestic installations, there is probably only one circuit that is particularly likely to experience an excessive total leakage - so that an RCBO (just for that circuit) might be almost as likely to trip as an RCD which was protecting the circuit (as well as other circuits) - although, as above, an RCBO trip would have less widespread impact.

Kind Regards, John

 

[JohnW2]

Aren't two separate lots of regulations being confused? ... Ones for premises where high CPC current is expected and high-integrity earthing should be installed, and ones for dwellings where it is not.

They are certainly two different issues (and related regulations).

However, installation of high-integrity earthy will presumably do nothing to prevent the RCD trips for which eric would like to blame the designer?

Kind Regards, John

 

[EFLImpudence]

“Every installation shall be divided into circuits, as necessary, to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.”

 

[JohnW2]

“Every installation shall be divided into circuits, as necessary, to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.”

Indeed - that is what eric is talking about (and that regulation presumably applies to any installation, not just 'dwellings in which high CPC currents are not expected').

However, as I said, even when high CPC currents are expected, high-integrity earthing, per se, will do nothing to prevent 'unwanted tripping of RCDs' - the only solution then is to split the high current imbalance between two or more RCDs.

Kind Regards, John

 

[ericmark]

Following your logic an electrician can’t win. We don’t know why any RCD trips. If there is a fault in the circuit, the electrician should fix it. If is due to an appliance, or actions taken by the customer, there is no come back on the electrician. I will chat with the customer and take best effort to elicit faults. There is only so far any of us can go to protect circuits from leakage. Just as we can’t prevent overloading sockets, or running a lead across a room. As we move to a standard of RCBO for all circuits, the impact of leakage should reduce.

I would agree once we move to a standard of RCBO for all circuits then any trips can't really be placed at the electricians door, and with commercial I know my bosses would have told me no way for a cost of £10 do you risk a circuit tripping, approx £55 to £190 for a 14 way, so £135 that is nothing when compared with man hours and loss of production.

It is really only the domestic customer, and even then one freezer full, and again simply not worth fitting non all RCBO. But the house holder still seems to have consumer units with just two RCD's fitted, OK some times just £135 can tip the balance, but if the electrician says I recommend fitting a all RCBO consumer unit, and the owner selects to save money, then fair enough, not the electricians fault, but I will go to a house because of a tripping RCD and say think easy way is fit RCBO's and the owner says oh did not know you could get them, they have not been even offered to option of all RCBO.

Next door did not know, and it was only when I went into my second kitchen to work on his vacuum cleaner saying I take it down there so if it does trip will not need to reset clocks, he knew there was the option to have every circuit on it's own RCD. Comment well having all RCBO would likely cost another £150 he said that's nothing compared with loosing so much when one circuit trips. Clearly had it been on offer he would have gone for all RCBO.

Some electricians to be far do give the customer the option, but it seems rare, they get an EICR it suggests new CU, they ask how much, and say go ahead, and really they have no idea what is going to happen until latter when the RCD starts to trip. Of course you always get the guy how puts it one, I have seen where a landlord had a new CU fitted, and the tenant would ring him every time it tripped as he didn't want it fitted for some reason. He claimed he could not reach it without standing on a chair and that was dangerous. One reason I would not want to be a landlord. Same calling out plumber when the ball cock needs a slight adjustment to stop it leaking.

 

[JohnW2]

I would agree once we move to a standard of RCBO for all circuits then any trips can't really be placed at the electricians door ....

Eric, you seem to be rather inconsistent in your views.

If you feel that a designer should be 'held responsible' if he/she (presumably with some knowledge or guesswork about 'probable loads') creates a situation in which there are RCD trips because of excessive total leakage current, then why would he/she not be equally 'responsible' if they (presumably with some knowledge or guesswork about 'probable loads') created a situation in which there were RCBO trips because of excessive total leakage current in the circuit protected by the RCBO?

As I wrote earlier, I would think that in most domestic installations, there is probably only one final circuit that is very likely to have excessive total leakage currents. When that is the case, then trips may well be almost as likely if the designer protects that circuit with an RCBO as when the circuit (plus others) was being protected by an RCD. In that situation, the culprit circuit needs to be split into more than one, not simply transferred 'in toto' to one RCBO.

However, as I've said, in the real world the designer of a domestic installation will rarely have a clue as to what loads will/may be plugged into a sockets circuit in the future, so (unless they are provided with that information, or a crystal ball) all they can really do is follow 'common/standard practice for domestic installations' in deciding what to design - and (for non-RCBO installations) I doubt that common/standard domestic practice will often involve three or more RCDs.

Kind Regards, John

 

[ericmark]

To my mind we have in the main two ring finals, and likely as you say move them to a RCBO and then tripping is down to a minimum, yes cooker, immersion, and other items with mineral insulated heaters can cause problems, but as long as on a double pole isolator they are easy enough to isolate when faulty and they are clearly faulty, and that is what the RCD is for, to trip when there is a fault.

The reverse is also possible, run the lights off a RCBO and then you don't lose lights with any sockets, maybe also the fridge/freezer as one it is a likely cause of tripping with the defrost heater, and two if A1 you don't want it to fail because some other device has caused a trip.

But the whole idea is it is planned, some thought has gone into how and where the RCD protection is split, I will hold up hands and admit I was not watching the rewiring of my mothers house close enough, I caught him about to include the sub main for kitchen on a general RCD and got him to feed it from a MCB the second consumer unit being fed with SWA and all RCBO. However I missed how he had split rest of house, and a fault in the garage caused loss of lights in the house. It seemed the CU wiring was rather random, no thought taken to what would happen if either RCD tripped.

i.e. it was not designed, the house was wired in the main by two men, but at the end of week not finished, so it was flooded with labour to finish it off, and most the items found latter which were not as asked for, were done in that last day. But it did what I wanted, I could if required let the house to help pay for mothers care, or use the house to look after mother in her final years with not worry about rubber insulated cables and not RCD protection, and after her death it was sold.

And as you suggest, with 4 circuits on RCBO and two on RCD the only trips were due to a fault, not a random trip, so it complied with the division of circuits, my own house however did not, two RCD's were not enough, and we did get random trips without any good reason, this house now is all RCBO and as with mothers only trip was with good reason, roof leaked.

In mothers house and this house a 100 mA RCD would have tripped with the faults, with real faults 95% of the time a 100 mA RCD will protect as it trips before any one touches it, using a class II drill with a metal gear box yes you can drill through cables and need that 30 mA protection but most real faults happen gradually with water ingress, and a 100 mA will trip before anyone touches a live part. But now we have no option, and 30 mA or could be just 16 mA is not much of a leakage, and all cables have some leakage with AC, and I don't have a clamp on meter that can measure 1 mA would need to use the Mk 8 AVO and so I simply don't know how close to the wind I am sailing, may be it should be a requirement to enter on the installation certificate what the leakage is when installed? And there should be more attention paid to this? But still feel there is a lazy-fair attitude to installation design and when electricians get it wrong they should be brought to task.

 

[EFLImpudence]

Indeed - that is what eric is talking about (and that regulation presumably applies to any installation, not just 'dwellings).

Yes, so in 'dwellings in which excessive CPC currents are not expected' that regulation is not relevant.

However, as I said, even when high CPC currents are expected, high-integrity earthing, per se, will do nothing to prevent 'unwanted tripping of RCDs' - the only solution then is to split the high current imbalance between two or more RCDs.

No, high-integrity earthing will not prevent the tripping but in such a situation it is a requirement. How many dwellings have it?

Equally, excessive CPC current itself does not cause an RCD to trip so perhaps another case of a poorly worded regulation.

 

[bernardgreen]

I do not know if this transcript is accurate, it has several spelling mistakes ( removed in case they were source tracers )

Description found in BS7671 18th Edition Regulation 543.7.1.203

"The wiring of of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective current is likely to exceed 10mA, shall have a high integrity protective connection complying with one of the following:

(i) A single protective conductor having a cross-sectional area of not less than 10mm², complying with the requirements of Regulations 543.2 and 543.3

(ii) A single copper protective conductor having a cross sectional area of not less than 4mm², complying with the requirements of Regulations 543.2 and 543.3, the protective conductor being enclosed to provide additional protection against mechanical damage, for example , within flexible conduit

(iii)Two individual protective conductors, each complying with the requirements of section 543. The two protective conductors may be of different types, such as the armouring of a SWA cable combined with an integral cpc..

Which to me suggests that a ring final supply with 3 or more computers ( each 3.5 mA on to CPC from in line main filters ) should have a CPC that is 4mm² CSA .

If that quote is accurate which I sincerely hope it is not then in the case of (1) a Live to Earth short circuit and (2) the protection devices failing to operate then the Live conductor will melt before the CPC melts. I guess that is the safer option.

Yes I do accept that failure of all protective devices is extremely unlikely to happen. But 10 mm², of course it will take a rat much longer to chew through 10mm² of copper than the same rat munching a 4mm² copper cable. ( maybe aluminium )


I assume that transcript has to be the author's own mis-understanding of the regulation, but then the regulations do seem to written by a committee whose members know very little about the reality of electricity.

 

[JohnW2]

Yes, so in 'dwellings in which excessive CPC currents are not expected' that regulation is not relevant.

I'm getting a bit confused:

Firstly, I've just realised that what you quoted ("Every installation shall be divided into circuits, as necessary, to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.") is slightly different from the wording of 314.1 ("...Every installation shall be divided into circuits, as necessary, to: ..... (iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not due to a fault"). What reg were you quoting?

In any event, one can but presume that the reason why eric felt that the designer would be 'at fault' in the situation he described (and therefore should rectify things at his/her own cost, if not sent to the gallows) was that he feels that the designer should have "expected excessive CPC currents", and designed accordingly?

No, high-integrity earthing will not prevent the tripping but in such a situation it is a requirement. How many dwellings have it?

Even though essentially rhetorical, I'm happy to agree by answering "almost none". However, it was you who brought high-integrity earthing into the discussion, and I'm not yet sure what your point was.

Equally, excessive CPC current itself does not cause an RCD to trip so perhaps another case of a poorly worded regulation.

I imagine that many would say that that is verging on the 'pedantic'

It is obviously literally true that CPC current does not cause an RCD trip. It is also true that if piece(s) of equipment result in L-'E' leakage ("not due to a fault"), then some of that current could pass to earth via a 'parallel path' (if one existed - e.g. if a Class I item were used outdoors with its exposed-c-p in contact with wet soil), rather than all going through the CPC.

However, I think it's also true that if equipment were going to produce enough leakage current to trip an RCD ("not due to a fault"), that would remain true even if there were no parallel path to earth, with all the 'leakage' current then going through the CPC.

Kind Regards, John