Quick Question re: Garage

[JohnW2]

Though sometimes people experience thermally damaged plugs and sockets with only a single plug in a single socket..........

They do.

It was also written in a time when H&S wasn't anything like as extreme as it is today.

Very true, but it was based on what would seem to be somewhat iffy assumptions. They surely must have realised that virtually all users would believe that it was appropriate to plug any 13A load into any "13A outlet", even if the outlet was one of two in a double docket?

I think there is a big difference between how safety authorities view new things and existing things.

Very much so - as people would discover if they tried to introduce asprin or paracetamol (at least, as non-prescription medicines), alcohol or tobacco for the first time in 2021 - I seriously doubt that any of them would stand much of a chance!

Presumably the safety authorities have not seen enough issues caused by overloaded double sockets to push for changing the standards.

Probably true. Indeed, I doubt that anyone has "seen enough issues caused by overloaded double sockets" to warrant any changes. Some people do experience thermally-damaged double sockets (and, as you say, also single ones) but I have personally never heard of one causing a fire (or any other major problem) - and the smell associated with 'serious thermal damage' will usually alert people to the problem before anything disastrous has a chance to happen.

Kind Regards, John

 

[plugwash]

Very true, but it was based on what would seem to be somewhat iffy assumptions. They surely must have realised that virtually all users would believe that it was appropriate to plug any 13A load into any "13A outlet", even if the outlet was one of two in a double docket?

The guidance for the rings and spurs supplying those sockets makes the same "iffy assumption" that it's unlikely for a high concentration of load to be placed in a single location.

IIRC it even used to be considered acceptable to have two seperate single sockets on a spur.

 

[EFLImpudence]

IIRC it even used to be considered acceptable to have two seperate single sockets on a spur.

I presume you mean an unfused 2.5mm² spur.

It still is acceptable despite some thinking it is not.

 

[JohnW2]

The guidance for the rings supplying those sockets makes the same "iffy assumptions".

I wouldn't personally say that. Although 'a risk' exists, both the regs themselves and associate guidance require/advise on the minimisation of that risk.

As for the regs themselves, 433.1.204 includes "... if, under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable." and Appendix 15 contains several items of advice/guidance as to how one can attempt to comply with the regulation.

Of course, sockets circuits are essentially a designer's nightmare, since, in the final analysis, he/she has no control over what might be plugged into the circuit. If there are umpteen '13A outlets', then .... The best he/she could do would be to avoid having any sockets near either end of the ring, in which case no part of the cable of the circuit could be overloaded IF the total load did not exceed the In of the OPD - but even that could theoretically lead to some overload 'of a part of the cable' for an indefinite period, and higher degrees of overload for 'appreciable periods' if a total load >In were connected.

Kind Regards, John

 

[JohnW2]

I presume you mean an unfused 2.5mm² spur. It still is acceptable despite some thinking it is not.

Yes, despite 'guidance' (Appendix 15), it would still be acceptable (to the regs themselves) if the 2.5mm² cable were 'Method C'.

Kind Regards, John

 

[plugwash]

Of course, sockets circuits are essentially a designer's nightmare

Exactly, if you consider two 13A loads plugged into the same double socket a risk worth mitigating then surely you would also consider two 13A loads plugged in near the same end of the ring (whether into the same double socket or not) or two 13A loads on the same spur to be a risk worth mitigating, yet I've never heard of any installer deliberately making a ring longer to avoid putting loads near the end of the ring.

Now of course if you assume "method C" and no grouping factors or other derating factors then 2.5mm² T&E has a significant margin above the regs-required 20A, but I question how often in a real installation that 100% of the run to the CU will be method C with no grouping factors. Afaict most installations have a large bunch of cables coming in to the CU, often enclosed in trunking.

 

[winston1]

Very much so - as people would discover if they tried to introduce asprin or paracetamol (at least, as non-prescription medicines), alcohol or tobacco for the first time in 2021 - I seriously doubt that any of them would stand much of a chance!

Not so sure about that.
Vaping products seem to have been introduced in most countries with no problem. Thailand has banned them however. Canada has restrictions but addicts pop down south to buy.

 

[JohnW2]

Exactly, if you consider two 13A loads plugged into the same double socket a risk worth mitigating then surely you would also consider two 13A loads plugged in near the same end of the ring (whether into the same double socket or not) or two 13A loads on the same spur to be a risk worth mitigating, yet I've never heard of any installer deliberately making a ring longer to avoid putting loads near the end of the ring.

Well, personally speaking, I regard them as rather different situations (i.e. different 'risks' that are being mitigated).

As far as cables are concerned, I'm afraid that I am fairly pragmatic in my approach (even if it attracts flak ), since even moderate degrees of theoretical 'overload' of cables for appreciable periods of time are not, in reality, going to do any harm to anything - I therefore cannot get very excited about that. However, visibly scorched and/or smelling plugs/sockets are a different matter, and are things which I would not want to carry on living with.

Now of course if you assume "method C" and no grouping factors or other derating factors then 2.5mm² T&E has a significant margin above the regs-required 20A, but I question how often in a real installation that 100% of the run to the CU will be method C with no grouping factors. Afaict most installations have a large bunch of cables coming in to the CU, often enclosed in trunking.

Again, waiting for flak, I wonder how many people bother to even think about minor occurrences of 'grouping' such as you mention - since I certainly don't. In any event, even if CCC is only 20A (the minimum permissible for a ring final) a designer could, if they so wished, ensure that no 'cable overload' would occur (with total loads ≤In) by not installing sockets within the appropriate distance from an end of a ring.

Kind Regards, John

 

[JohnW2]

Not so sure about that. Vaping products seem to have been introduced in most countries with no problem.

They have, but I think only as the lesser of evils (in comparison with what already exists legally). If tobacco didn't exist and/or was 'illegal', I very much doubt whether 'vaping products' would have been allowed to appear legally.