two ring mains joined

[JohnW2]

The radial circuit arrangements offer increased safety over the ring (in its present standard form) ....

.... other than in terms of CPC redundancy.

... so why don't they promote those and abandon rings entirely?

As I've just written, I imagine that they are under constant pressure from some quarters to do just that.

Kind Regards, John

 

[securespark]

Does it say 'should'?

No. It says "shall".

 

[PBC_1966]

.... other than in terms of CPC redundancy.

True. So if they were were trying to combine the two aspects of providing extra earth integrity and eliminating the possibility of overload, they could specify radials with an extra earth conductor "just to make sure." Or specify that 30A rings be run in 4 sq. mm minimum. Or keep 2.5 sq. mm but only allow 20A protection.

The point I was trying to make is that "they" might not always acknowledge what would be better, or there are numerous things which "they" could do.

 

[EFLImpudence]

No. It says "shall".

Ok, fair enough.


Does it also say window frames shall be bonded?

 

[JohnW2]

True. So if they were were trying to combine the two aspects of providing extra earth integrity and eliminating the possibility of overload, they could specify radials with an extra earth conductor "just to make sure."

They already do, but only in situations (of high anticipated 'leakage') that require 'high integrity earthing'. One imagines that what you suggest would only have appreciable effect if they 'banned' current-day ('low integrity earthing') radials!

... Or specify that 30A rings be run in 4 sq. mm minimum. Or keep 2.5 sq. mm but only allow 20A protection.

Again, unless they 'banned' radials, I suspect that no-one would bother to install rings under those rules!

Kind Regards, John

 

[ban-all-sheds]

Why not? Are you perhaps just trying to be 'clever'

I have no need to do that.

by thinking of a situation other than that (which is obviously what I was talking about) of a 2.5mm² unfused spur (from a 32A ring final) that is supplying multiple sockets? If not, please clarify.
Again, unless you are thinking of something other than what I was obviously talking about (a 2.5mm² 32A radial sockets circuit), please clarify.

An unfused spur is a "circuit" like any other. Ignoring what is or is not a "circuit", it has a cable with a certain capacity, it has a design load (perhaps) and it has a protective device.

There is no need for it to have its own prescriptions and proscriptions in the regulations as it is already dealt with perfectly well by existing regulations.

Again, unless you are thinking of something other than what I was obviously talking about (a 2.5mm² 32A radial sockets circuit), please clarify.

I did think that the discussion had become more generic:

I forgot to add - supplying a fixed appliance via an FCU is obviously not a "non-fused spur".

But if you want to focus only on socket circuits then that's fine. I see no problem with declaring that the Ib of a spur with 2 sockets, singles if you like, to be 26A. That is, installation method permitting, less than Iz. The nature of loads connected by BS 1363 plugs & sockets is that they cannot cause an overload, and as we all know, a B32 is fine for fault protection on 2.5mm² cable.

So the regulations do permit a 2.5mm² 32A socket radial (and therefore also an unfused spur). Put more than two sockets on it though and it becomes much harder to justify a 26A Ib

 

[JohnW2]

So the regulations do permit a 2.5mm² 32A socket radial (and therefore also an unfused spur). Put more than two sockets on it though and it becomes much harder to justify a 26A Ib

That's the point - that, since the regs appear to allow an unfused spur from a ring final to have a CCC as low as 20A, then (regardless of the In of the OPD) it would clearly not be acceptable (or compliant), in terms of other regulations, to have that cable supplying a load with an Ib >20A. By suggesting (in the 'informative' Appendix) one double socket, but not two single sockets, they are presumably assuming that a double socket represents a maximum load of 20A.

Kind Regards, John

 

[PBC_1966]

By suggesting (in the 'informative' Appendix) one double socket, but not two single sockets, they are presumably assuming that a double socket represents a maximum load of 20A.

Which I believe is what some manufacturers specify as the total allowable current for a double socket, even though we know that in practice there's nothing to stop somebody plugging two 3kW loads into one. And at one time the regs. did allow two single sockets to be run on a non-fused spur, with no stipulation about the location of the two sockets in relation to each other.

 

[JohnW2]

Which I believe is what some manufacturers specify as the total allowable current for a double socket, even though we know that in practice there's nothing to stop somebody plugging two 3kW loads into one.

Indeed, but even the manufacturers don't seem to be sure what they are specifying. You will recall that I got essentially nowhere talking to an MK techie about what they mean by "13A per socket outlet", although there is an MK document knocking around that appears to indicate socket damage at 22A continuous and 'serious damage' at 24A. However, I would probably have expected that the regs would (should) consider the possibility that two plugs with 13A fuses (and 3kW loads) could be plugged into a double socket. I'm sure that very very few members of the general public even dream of the fact that such is not 'OK'.

Kind Regards, John

 

[securespark]

Ok, fair enough.


Does it also say window frames shall be bonded?

Seen that done under the 15th in my Gran's house in Guildford...with a link across to the opening light.

 

[ban-all-sheds]

That's the point - that, since the regs appear to allow an unfused spur from a ring final to have a CCC as low as 20A, then (regardless of the In of the OPD) it would clearly not be acceptable (or compliant), in terms of other regulations, to have that cable supplying a load with an Ib >20A.

So what?

Worst case CCC for 2.5mm² is 13.5A. I really don't see what your point is. There are already existing regulations which prevent people from designing circuits where all or part of them will be subjected to overload - I can't see what could be done in compliance with the regs today which could not be done if unfused spurs were explicitly prescribed tomorrow.

By suggesting (in the 'informative' Appendix) one double socket, but not two single sockets, they are presumably assuming that a double socket represents a maximum load of 20A.

I think all one can safely assume is that they are assuming that the spur cable might not have a CCC of at more than 20A, and that 2 single sockets represent a load of 26A.

 

[ban-all-sheds]

As I've just written, I imagine that they are under constant pressure from some quarters to do just that.

Not least from the makers of structured wiring systems, who probably have a great deal of lobbying clout.

 

[JohnW2]

There are already existing regulations which prevent people from designing circuits where all or part of them will be subjected to overload.

There are and, were it not for the 'dispensation', those regulations would preclude ring finals as we know them.

Kind Regards, John

 

[ban-all-sheds]

True.

I still don't see what your point is. A spur is not a ring.

 

[JohnW2]

I still don't see what your point is. A spur is not a ring.

Indeed it isn't. However, 433.1.204 appears to be saying that a ring final ("with or without unfused spurs") may be wired in cable with a CCC of 20A and the guidance in Appendix 15 suggests that such a spur may supply a double socket. Since that cable may well only be protected from overload by two 13A fuses (downstream), unless the designer has a crystal ball which can tell him/her that the load will never be >20A, such a circuit would be non-compliant with other regulations. It therefore seems as if only 'the dispensation' as regards ring finals (and spurs therefrom) allows what would otherwise (without that crystal ball) be non-complaint if it were, say, a 20A CCC cable supplying just one double socket as a 32A radial.

... or do you perhaps believe that a 32A radial supplying one double socket, wired in cable with a CCC of 20A, would be compliant?

Kind Regards, John