Myths

[JohnW2]

Anyway, compliance aside, my opinion is NO it has not become any more risky/dangerous to remove the ring and leave everything else as it was. ... It can`t be.
Electrons do not care about topology.

Quite so.

The discussion/argument all centres around the question of whether or not the 'minimum CCC' of 20A 433.1.204 applies to unfused spurs as well as to the ring itself. As I've said, the words of the reg seem to me (and presumably SUNRAY, and probably others) to be saying that it does apply to the spur cable, but some, certainty EFLI, appear to feel strongly to the contrary.

Do you have a view? (you appear to have agreed with my interpretation in post #55)

Kind Regards, John

 

[Diver Fred]

There was a requirement for switches for fixed appliances in bathrooms to be of the pull cord type, but only if the switch was in the bathroom, and that last appeared in the 13th edition in 1962.

View attachment 325609

However even then it was permitted for the switch to be located outside the room, so the 'electric board' person was still wrong.
That requirement was removed in the 1966 edition.

This may be where the 'pull cords required for bathroom lights' mess originated from, although it was only ever a requirement for fixed appliances. Lights never needed a pull cord in bathrooms or anywhere else.

The fan heater had it's own integrated pull cord operated switch. The switched FCU was outside, above the bathroom door (where most people have such such switches/protection).

 

[ebee]

Well, not usually "1, 2 OR 3" reasons - isn't it usually 'all three of them' ?

Not always John, often it is but some might be dealt with by other means. Overload is a common one, fixed loads that have a maximum rating such as an electrical shower for example.
Obviously a cluster of sockets can commonly overload the cable, they might do rarely if ever but yes, unless the number on the circuit is so small that plugtop fuses negate it we can not rely on floorspace estimations etc because overload is quite possible. A motor stalling to some extent could cause overload etc etc. A fixed heater such as an immersion heater could not overload.
Short circuit protection is just about always needed.
Earth fault is often needed but we could put some reliance on an RCD , however unless TT we usually use the MCB/Fuse etc for eartgh fault protection and if an RCD is present we include it as back up.
So overload not needed on a fixed load really.

 

[ebee]

Quite so.

The discussion/argument all centres around the question of whether or not the 'minimum CCC' of 20A 433.1.204 applies to unfused spurs as well as to the ring itself. As I've said, the words of the reg seem to me (and presumably SUNRAY, and probably others) to be saying that it does apply to the spur cable, but some, certainty EFLI, appear to feel strongly to the contrary.

Do you have a view? (you appear to have agreed with my interpretation in post #55)

Kind Regards, John

I am happy to agree with your interpretation John but I do pay respects to ELFI in his logic take too, I can see what he is thinking, we do not allow it on radials so why in this one case? after all a spur is in reality a radial supplied by a ring rather than directyly from the fuseway so in actuallity not different. Think of it as a "get out of jail free card" in this instance!

 

[EFLImpudence]

Surely the argument cannot stand and is indeed rendered futile (even if it did apply to unfused spurs) because 433.1.204 states that:

"The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm2 except for two-core mineral insulated cables"

So, the situation cannot arise.

 

[SUNRAY]

Surely the argument cannot stand and is indeed rendered futile (even if it did apply to unfused spurs) because 433.1.204 states that:

"The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm2 except for two-core mineral insulated cables"

So, the situation cannot arise.

Which seems to distinctly rule out the often suggested use of 4mm² spurs if that is the wording related to ring finals.

 

[JohnW2]

I am happy to agree with your interpretation John but I do pay respects to ELFI in his logic take too,

Same here. I've already agreed with EFLI that what the regs appears to say is nonsense, and that the requirement for the CCC of cable in an unfused spur should be no different from the situation with any other radial - BUT I do believe (as you also seem to) that the reg, has been written in a manner which gives it that 'nonsense' meaning.

I can see what he is thinking, we do not allow it on radials so why in this one case? after all a spur is in reality a radial supplied by a ring rather than directyly from the fuseway so in actuallity not different.

Exactly. As above, that why I've agreed with him that it is 'nonsense', but nonsense is what the words of the reg, as written, appear to say!

Kind Regards, John

 

[JohnW2]

Surely the argument cannot stand and is indeed rendered futile (even if it did apply to unfused spurs) because 433.1.204 states that:
"The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5 mm2 except for two-core mineral insulated cables"
So, the situation cannot arise.

What situation 'cannot arise' ?

You surely aren't suggesting that the CCC of 2.5mm² T+E cannot be reduced to 20A as a result of 'de-rating factors'?

I though that the 'fiddles' in Table 4D5 (in comparison with 4D2A) were introduced to allow Method A (and also Methods 100 and 102) 2.5mm² T+E to comply with the CCC requirement of 433.1.204, weren't they?

Kind Regards, John

 

[Murdochcat]

Wasn't Murdochcat referring to a radial final circuit?

No

Ring
Final
Circuit

 

[JohnW2]

I can see what he is thinking, we do not allow it on radials so why in this one case? after all a spur is in reality a radial supplied by a ring rather than directyly from the fuseway so in actuallity not different.

As you know, I agree with that. However, there is one implication that we haven't discussed.

If EFLI believes that the "20A minimum CCC" of 433.1.204 does not apply to the cable of unfused spurs from ring finals (which should just be treated as 'any other radial') then he presumably also doesn't think that the "minimum 2.5mm²" applies to those unfused spurs, either ?

That being the case, I wonder if he would regard it as acceptable for an unfused spur from a ring supplying just one single socket to be wired in 1.5mm² cable (all but Method 103) - or, indeed, now even 1.0mm² (Method 100, 102 od C) ?

Kind Regards, John

 

[JohnW2]

Not always John, often it is but some might be dealt with by other means. Overload is a common one, fixed loads that have a maximum rating such as an electrical shower for example.

Fair enough. There are some stations in which the regs allow omission of overload protection, primarily when the nature of the load is such that it is 'unlikely to result in an overload current' (usually purely resistive loads) - but, as you will often see here, it is nearly always a contentious issue, with some people always willing to think up ways in which almost any load can (very rarely) result in overload current.

Short circuit protection is just about always needed.

Interestingly, although you mentioned it as 'one of the 3 protections', BS7671 really only talks about overload and fault protection. I don't think there is any situation in which BS7671 permits the omission of both overload and fault protection and if either (or both) of those is present, that will inevitably also provide 'short-circuit protection' - so that doesn't really need to be considered as a separate 'protection'.

.... So overload not needed on a fixed load really.

I'm nor sure what you mean by 'fixed' but, as above, there are limited situations in which overload protection may be omitted, and most of those are to some degree contentious. If the load is not purely resistive, and particularly if it involves significant motors, overload protection is likely to be required.

Kind Regards, John

 

[EFLImpudence]

What situation 'cannot arise' ?

You surely aren't suggesting that the CCC of 2.5mm² T+E cannot be reduced to 20A as a result of 'de-rating factors'?

I though that the 'fiddles' in Table 4D5 (in comparison with 4D2A) were introduced to allow Method A (and also Methods 100 and 102) 2.5mm² T+E to comply with the CCC requirement of 433.1.204, weren't they?

Kind Regards, John

Yes, sorry again. I forgot about the derating.

The more I read the regulation, the dafter it gets.

 

[EFLImpudence]

If EFLI believes that the "20A minimum CCC" of 433.1.204 does not apply to the cable of unfused spurs from ring finals (which should just be treated as 'any other radial') then he presumably also doesn't think that the "minimum 2.5mm²" applies to those unfused spurs, either ?

I do not. There is no reason it should apply to the ring using 32A MCBs as opposed to 30A BS3036s for wich the regulation is still written.

That being the case, I wonder if he would regard it as acceptable for an unfused spur from a ring supplying just one single socket to be wired in 1.5mm² cable (all but Method 103) - or, indeed, now even 1.0mm² (Method 100, 102 od C) ?

Yes, I would as long as the derating and fault conditions are met.

 

[EFLImpudence]

No

Ring
Final
Circuit

Ah, right. Only you wrote RFC.

 

[ericmark]

I do like the ring final circuit, but I also accept it has a problem where sockets are too close to the origin to ensure the 20 amp per leg is not exceeded.

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:
(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile frog the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit
(iv) taking account of the total floor area being served. (Historically, limit of 100 m² has been adopted.)

This is clearly to reduce the chance of an over load, but the radial idea does not get away Scot free either, as having unfused spurs from a 4 mm² or 6 mm² cable presents a problem getting the cables into the socket, and using 20 amp causes problem with inrush on items like 110 volt transformers.

I am sure we could today develop another design to get around the problems, but to get it to integrate with what we already have would be the problem. We have to accept the system was designed to be run as a ring final, and accept in general it is still the best system for use with our 13 amp sockets.

I do feel we need a 16 amp fused connection unit taking a fuse something like this for use on cooker supplies and the like to feed ovens, but from a radial not a ring final, and it would need to be made clear not for use on a ring final. Mainly to allow a 32 amp or larger supply to feed multi items designed for Europe where a 16 amp supply is standard.

However I also see the problems, some one is bound to try fitting one on a ring final. But to me these may do the job, but are not aesthetically pleasing and I would not want one on my kitchen wall. I am sure a unit like a cooker connection unit could be produced to take one 16 amp fuse. However also the appliance could incorporate an overload like these so it could be safely supplied from a 40 amp supply, or even a panel fuse.

The

433.2.2 The device protecting a conductor against overload may be installed along the run of that conductor
if the part of the run between the point where a change occurs (in cross-sectional area, method of installation, type
of cable or conductor. or in environmental conditions) and the position of the protective device has neither branch
circuits nor outlets for connection of current-using equipment and fulfils at least one of the following conditions:
(i) It is protected against fault current in accordance with the requirements stated in Section 434
(ii) Its length does not exceed 3 m, it is installed in such a manner as to reduce the risk of fault to a minimum,
and it is installed in such a manner as to reduce to a minimum the risk of fire or danger to persons (see also
Regulation 434.2.1).

I am told does not include unfused spurs, I have not yet worked out why this does not limit the length of an unfused spur, I know it is to allow small cross section cabled from the bus bar chamber to the distribution units within a switch room, but it does not say that, so I would think it does apply to unfused spurs, and those who believe it does not, realise they have run over length unfused spurs and don't want to admit they got it wrong?

The BS 7671 is not published in Welsh, or any other British language other than UK English, and I can understand why, as it is hard enough to prevent any ambiguity in English never mind translating into Welsh. It is so easy to do, I remember the sign on the old A6 before the M6 opened, it said "Beware of the man eating haggis" clearly they wanted the duel meaning, but we don't what that in the regulations, we had this with wires coloured green and yellow, I have seen so many tank thermostats where the green/yellow core was a line wire, but fed with flex and held on with a Bungy cord so not really fixed, so does not require an earth, but ask anyone doing the PAT testing why there is no label on it, and one gets don't be daft that's part of the EICR, and if part of the installation then it needs an earth wire.

This what is current using equipment, and what is part of the installation has been argued about since I started my apprenticeship, we all I think accept lights is part of the EICR in spite of them using current, but it seems nothing else is considered part of the installation. But seen reports with a C2 code for missing smoke alarms, how can some thing being missing what ever it is, cause a potential electrical danger? Unless bare wires left where it should go.