The most basic problem with DIY work

[EFLImpudence]

So what does that mean in terms of how you would treat it for an EICR?

As you have to quote a regulation number now it may be difficult.

Does that mean that you'd feel obliged to 'pass' it (1.5mm² protected by B32 or B40) because you did not feel that the immersion was likely to overload the cable?

Can the immersion cause an overload?
If not, which regulation do you think it contravenes?

... So what about the much more real-world scenario, of some simple lighting circuitry (maybe in a garage or outhouse) fed in 1mm² cable as a 'spur' from a 32A sockets circuit without any 'fusing down'? Would that 'pass' your EICR?

The installer would have to test for various things so he would be better off fitting a fuse so I think it may be getting too hypothetical.

I don't really understand that. What various things would (s)he need to test if there were no FCU that (s)he wouldn't need to test if there were one? Nor do I really see why it's hypothetical. If you and others really felt that it was not only compliant but also reasonable to run lighting (maybe in 1.5mm² cable - see below) straight from a 32A-protected circuit, without any intermediate fuse, wouldn't/shouldn't you all be suggesting that 'simple solution' for the garage/shed lighting we so often get asked about in this forum? Why would you tell them to buy and install an FCU if you didn't feel it was necessary?

434.
I don't think I have advocated the situation.
I am merely trying to answer your (devil's advocate) questions.

Also, 1mm² is not allowed for power circuits or is that no longer a power circuit being a spur without a fuse for lighting.?

Well, there's certainly a debate to be had there, but I can short-circuit the need for it by saying 1.5mm² - which leaves the basic issue (32A OPD protection) still there.

Again, it either complies or it does not.
It depends on whether the load can overload or not.
If not, which regulation do you think it contravenes?


I just cannot envisage these scenarios occurring.
Who would, when installing a 1.00 or 1.5mm² lighting circuit think " I will fit a 32A MCB for devilment" and look forward to a lengthy argument with someone.

 

[JohnW2]

Does that mean that you'd feel obliged to 'pass' it (1.5mm² protected by B32 or B40) because you did not feel that the immersion was likely to overload the cable?

Can the immersion cause an overload? If not, which regulation do you think it contravenes?

Well, it's your view about that (when deciding how to complete an EICR) which I've been trying to get out of you We are agreed that if an immersion cannot cause an overload that there would be no regulations contravened. My question to you is whether, when completing an EICR, you would, or would not, take the view that an immersion cannot cause an overload.

I don't really understand that. What various things would (s)he need to test if there were no FCU that (s)he wouldn't need to test if there were one?

434

Do you mean that you wouldn't bother to undertake tests to confirm that the fault protection (i.e. disconnection times) was adequate if you had fitted an FCU?

I don't think I have advocated the situation. I am merely trying to answer your (devil's advocate) questions.

I'm not sure that I'm really being a devil's advocate here. I think my position is fairly clear - I wouldn't dream of suggesting that anyone should connect lighting circuitry direct to a 32A circuit, even with 1.5mm² cable, without an intervening FCU. However, if there are those who believe that lighting 'cannot' result in an overload of the cable, then I would expect them to be suggesting just that.

I just cannot envisage these scenarios occurring. Who would, when installing a 1.00 or 1.5mm² lighting circuit think " I will fit a 32A MCB for devilment" and look forward to a lengthy argument with someone.

As you say, there would be no sense in that. However, as above, there's a genuine scenario in which it could (and does) often arise - not a dedicated 1mm² or 1.5mm² lighting circuit protected by a 32A MCB (which would be plain daft, and totally unnecessary) but, rather, connecting such a lighting 'circuit' to an existing 32A-protected sockets circuit in a garage, shed or whatever.

Kind Regards, John

 

[EFLImpudence]

Does that mean that you'd feel obliged to 'pass' it (1.5mm² protected by B32 or B40) because you did not feel that the immersion was likely to overload the cable?

Can the immersion cause an overload? If not, which regulation do you think it contravenes?

Well, it's your view about that (when deciding how to complete an EICR) which I've been trying to get out of you We are agreed that if an immersion cannot cause an overload that there would be no regulations contravened. My question to you is whether, when completing an EICR, you would, or would not, take the view that an immersion cannot cause an overload.

I don't see how it can cause an overload but I don't see how the situation would arise unless someone had gone out of their way to install it on purpose for no reason.

I don't really understand that. What various things would (s)he need to test if there were no FCU that (s)he wouldn't need to test if there were one?

434

Do you mean that you wouldn't bother to undertake tests to confirm that the fault protection (i.e. disconnection times) was adequate if you had fitted an FCU?

No, but there are further things to consider with non standard circuits.

I don't think I have advocated the situation. I am merely trying to answer your (devil's advocate) questions.

I'm not sure that I'm really being a devil's advocate here (Edit ). I think my position is fairly clear - I wouldn't dream of suggesting that anyone should connect lighting circuitry direct to a 32A circuit, even with 1.5mm² cable, without an intervening FCU. However, if there are those who believe that lighting 'cannot' result in an overload of the cable, then I would expect them to be suggesting just that.

Lighting CAN. A single light may not so perhaps it would be acceptable in an electrician's shed but in a customer's it would be undesirable as they could fit a light with a heater or similar - perhaps their fault but a fuse would prudent for their protection as well as the cable's.

I just cannot envisage these scenarios occurring. Who would, when installing a 1.00 or 1.5mm² lighting circuit think " I will fit a 32A MCB for devilment" and look forward to a lengthy argument with someone.

As you say, there would be no sense in that. However, as above, there's a genuine scenario in which it could (and does) often arise - not a dedicated 1mm² or 1.5mm² lighting circuit protected by a 32A MCB (which would be plain daft, and totally unnecessary) but, rather, connecting such a lighting 'circuit' to an existing 32A-protected sockets circuit in a garage, shed or whatever.

As above.

 

[JohnW2]

I don't see how it can cause an overload but I don't see how the situation would arise unless someone had gone out of their way to install it on purpose for no reason.

Fair enough. I'll take that to mean that you'd 'pass' it for an EICR if you ever came across it (which you won't). I've always said that the immersion example was an extreme (essentially ridiculous) hypothetical one - but the lighting case is a different kettle of fish...

Do you mean that you wouldn't bother to undertake tests to confirm that the fault protection (i.e. disconnection times) was adequate if you had fitted an FCU?

No, but there are further things to consider with non standard circuits.

Some learning for me, it seems ... what sort of 'further things' did you have in mind?

However, if there are those who believe that lighting 'cannot' result in an overload of the cable, then I would expect them to be suggesting just that.

Lighting CAN. A single light may not so perhaps it would be acceptable in an electrician's shed but in a customer's it would be undesirable as they could fit a light with a heater or similar - perhaps their fault but a fuse would prudent for their protection as well as the cable's.

Ah, right - so you're not 'one of them'. Fair enough. I thought we were talking about about whether or not the lighting circuit could be overloaded by faults, not future idiotic changes to the installation. Mind you, there's always the question of the extent to which design has to take into account possible future very unlikely changes (do we have to consdier the possibility of some future idiot connecting a cooker or shower to the immersion circuit?!). Particularly if we're talking about 1.5mm² cable, that could be 16A worth of 'light with a heater' that some idiot would have to install to overload the cable - and I think one would have to try extremely hard to find such a fitting (and would probably fail!)!

Kind Regards, John

 

[JohnW2]

I think that all this "Devil's Advocate" stuff (not just one one side!) is at risk of obscuring my position, which I thought I had made clear at the very start. So, to be clear .... It is my personal view that to be always totally sure/ cautious/ conservative/ 'safe'/ whatever, any cable (be it fixed wiring, an appliance flex or whatever) should be protected against overload current by an OPD (usually, but not always/necessarily upstream of the cable) whose In is no more than the CCC of the cable. That applies to plug fuses for appliance flexes, immersion circuits, lighting circuits or anything else. Any 'wriggling' out of that basic approach strikes me as unnecessary and potentially risky, even if the risks are, in some situations, undoubtedly very low

Kind Regards, John

 

[EFLImpudence]

Some learning for me, it seems ... what sort of 'further things' did you have in mind?

You would probably have to calculate if the cpc were large enough.

Ah, right - so you're not 'one of them'. Fair enough. I thought we were talking about about whether or not the lighting circuit could be overloaded by faults,

When? Why? That's not the definition of 'overload'.
Cable's ALWAYS have to be protected against fault current.

not future idiotic changes to the installation. Mind you, there's always the question of the extent to which design has to take into account possible future very unlikely changes (do we have to consdier the possibility of some future idiot connecting a cooker or shower to the immersion circuit?!). Particularly if we're talking about 1.5mm² cable, that could be 16A worth of 'light with a heater' that some idiot would have to install to overload the cable - and I think one would have to try extremely hard to find such a fitting (and would probably fail!)!

I know we don't have to future proof but leaving a 1mm² protected by a 32A opd at a customer's where anything could be done would be irresponsible.

I'm just trying to answer your questions; not promoting the practices.

I think that all this "Devil's Advocate" stuff (not just on one side!) is at risk of obscuring my position, which I thought I had made clear at the very start. So, to be clear .... It is my personal view that to be always totally sure/ cautious/ conservative/ 'safe'/ whatever, any cable (be it fixed wiring, an appliance flex or whatever) should be protected against overload current by an OPD (usually, but not always/necessarily upstream of the cable) whose In is no more than the CCC of the cable. That applies to plug fuses for appliance flexes, immersion circuits, lighting circuits or anything else. Any 'wriggling' out of that basic approach strikes me as unnecessary and potentially risky, even if the risks are, in some situations, undoubtedly very low

Unless of course they cannot be (overloaded).
Not in a hypothetical pointless way but where it may be useful or necessary.

 

[westie101]

do we have to consdier the possibility of some future idiot connecting a cooker or shower to the immersion circuit?!

Though I have seen a 7.5kw shower connected to a lighting circuit protected by a re-wireable fuse, strangely enough the house didn't burn down.
It does raise the question of just what factor of safety is there in the system?

Though in answer to the question, no.

 

[securespark]

Not seen anything quite that bad, but did find a 10.8 on 2.5 on a 30A 3036.

Think that was an ex-immersion circuit...

 

[JohnW2]

Some learning for me, it seems ... what sort of 'further things' did you have in mind?

You would probably have to calculate if the cpc were large enough.

Fair enough.

Ah, right - so you're not 'one of them'. Fair enough. I thought we were talking about about whether or not the lighting circuit could be overloaded by faults,

When? Why? That's not the definition of 'overload'.
Cable's ALWAYS have to be protected against fault current.

Sorry - bad choice of words. I didn't mean 'fault' in the BS7671 sense but, rather in the everday sense - i.e. something going wrong within the load which caused it to draw an excessive current (via either L-N or L-CPC), but well below the 'fault current' resulting from a BS7671 negligible impedance ('bolted') fault (e.g. like Simon's hypothesised immersion 'problem') - which is what I thought we were talking about. If we were only talking about overloads due to normally-functioning loads, it would then obviously be impossible for any fixed-wired fixed load to ever produce such an overload (if it didn't when first installed)

I know we don't have to future proof but leaving a 1mm² protected by a 32A opd at a customer's where anything could be done would be irresponsible.

It should be clear from what I've said that I agree - but it's a judgement that may differ from person to person. For anyone whose view is that the characteristics of the load (or 'possible future loads') is such that overload is 'unlikley', the setup would be compliant.

... So, to be clear .... It is my personal view that .... Any 'wriggling' out of that basic approach strikes me as unnecessary and potentially risky, even if the risks are, in some situations, undoubtedly very low[/color]

Unless of course they cannot be (overloaded).

If there are any situations in which you are (or anyone else is) absolutely certain that overload is impossible, then I'd have to agree - but I'm not convinced that any such situations actually exist. The moment that overload becomes 'a possibility' (even if remote), I would personally stick to my cautious approach.

Not in a hypothetical pointless way but where it may be useful or necessary.

Are you saying that you feel that there are some situations in which having a cable protected from overload by an OPD whose In is greater than the CCC of the cable is 'useful or necessary'?

Kind Regards, John

 

[JohnW2]

Not seen anything quite that bad, but did find a 10.8 on 2.5 on a 30A 3036.

"Don't tell anyone, but..." I suppose this is where the wide 'safety margins' come in. At 230V a 10.8 kW (at 240V) shower will only draw about 1.6 times the CCC of 2.5mm² clipped direct - and I rather doubt that such a degree of overload would, in reality, do any great harm.

Kind Regards, John

 

[EFLImpudence]

Not in a hypothetical pointless way but where it may be useful or necessary.

Are you saying that you feel that there are some situations in which having a cable protected from overload by an OPD whose In is greater than the CCC of the cable is 'useful or necessary'?

Well. in that case it wouldn't be protected from overload.

Why else would the regulations allow it?

 

[JohnW2]

Are you saying that you feel that there are some situations in which having a cable protected from overload by an OPD whose In is greater than the CCC of the cable is 'useful or necessary'?

Well. in that case it wouldn't be protected from overload.

Well, it would be 'protected' to some extent, even if not to the extent normally required by BS7671 [per implication of my most recent post, I strongly suspect that an OPD which only protected the cable from currents more than, say, double its CCC would probably prevent any great harm resulting]

Why else would the regulations allow it?

Being 'allowed' and being 'useful or necessary' (particularly 'necessary') would seem to be very different things. In what sort of circumstances would you personally consider it 'useful or necessary' to invoke 433.3.1(ii)?

Kind Regards, John

 

[securespark]

I rather doubt that such a degree of overload would, in reality, do any great harm.

Oh, it did, but to be fair, it took a while!

 

[JohnW2]

I rather doubt that such a degree of overload would, in reality, do any great harm.

Oh, it did, but to be fair, it took a while!

I have to say that I'm very surprised, particularly given the relatively brief, and infrequent, durations of use of a shower. What 'harm' resulted, eventually?

Kind Regards, John

 

[EFLImpudence]

Are you saying that you feel that there are some situations in which having a cable protected from overload by an OPD whose In is greater than the CCC of the cable is 'useful or necessary'?

Well. in that case it wouldn't be protected from overload.

Well, it would be 'protected' to some extent, even if not to the extent normally required by BS7671 [per implication of my most recent post, I strongly suspect that an OPD which only protected the cable from currents more than, say, double its CCC would probably prevent any great harm resulting]

Apart from going round in circles It would seem one of us is confused.

An appliance which cannot cause an overload (an overcurrent occurring in a circuit which is electrically sound) can be installed on an OPD whose rating is greater than the CCC of the cable because it (the cable) will not have to deal with loads greater than that of the appliance's stated rating for which the cable has been selected.
Should a fault occur the OPD will operate as this will have been determined.
That was what I thought wrong with Simon's hypothesis because, I don't think, an immersion can cause a fault current which is (as you mention) only double the cable's CCC.

Why else would the regulations allow it?

Being 'allowed' and being 'useful or necessary' (particularly 'necessary') would seem to be very different things. In what sort of circumstances would you personally consider it 'useful or necessary' to invoke 433.3.1(ii)?

The first that springs to mind is connecting a small oven to the cooker circuit by the supplied flex (MIs notwithstanding).
(I never recommend this on the forum because DIYers will not be able to test to ensure the other conditions are met and have stated that several times.)