Extending a ring, or a spur?

[JohnW2]

I thought I read on here they were likely to be rated at 13A x2

As I said, they are (and, I think, have always been) 'rated' at "13A per socket outlet" - but, as I said, even their Technical Support people could not tell me for certain what that means. However, as per post#9 above, it is MK who (at some point in the past) said that when total (continuous) current rises above 19.5A "Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period."

... unlike other brands which were 20A

As I've also said, despite the fact that such is a commonly held belief (quite probably based on the fact that the BS1363 test is carried out with 20A), I can't recall ever having seen a double socket, of any make, that says that it is "rated" at 20A - have you ever seen that?

Kind Regards, John

 

[john4703]

One of the interesting things about this forum is how an apparently simple question can lead to a lengthy discussion of the pros and cons and solutions. I have decided that if the floor level socket is on a ring main, (I will check that when I can have time in the building to turn of MCBs to find which feeds this socket) I will put three single sockets at a higher level. That solves the problem of overloading a twin socket and occasionally three would be useful. As far as I am concerned anything that stops people using 4 way extension leads for highish loads is good.

 

[JohnW2]

One of the interesting things about this forum is how an apparently simple question can lead to a lengthy discussion of the pros and cons and solutions. I have decided that if the floor level socket is on a ring main, (I will check that when I can have time in the building to turn of MCBs to find which feeds this socket) I will put three single sockets at a higher level. That solves the problem of overloading a twin socket and occasionally three would be useful. As far as I am concerned anything that stops people using 4 way extension leads for highish loads is good.

Assuming that you are talking about putting those three single sockets 'on the ring' (assuming that it is a ring!), then that sounds like a good plan.

Kind Regards, John

 

[john4703]

Assuming that you are talking about putting those three single sockets 'on the ring' (assuming that it is a ring!), then that sounds like a good plan.
Kind Regards, John

Thanks JohnW2, if it is not a ring I'll leave it as it is until a full rewire is possible..

 

[scousespark]

Thanks JohnW2, if it is not a ring I'll leave it as it is until a full rewire is possible..

If it is a radial circuit, you can just add your single sockets now. Do you know how to tell the difference and how to test your installation?

 

[john4703]

If it is a radial circuit, you can just add your single sockets now. Do you know how to tell the difference and how to test your installation?

I know I could add a socket safely but if it is a radial on a 20a breaker I'd worry about adding any more sockets as they could cause the breaker to trip as people would use them all.

 

[JohnW2]

I know I could add a socket safely but if it is a radial on a 20a breaker I'd worry about adding any more sockets as they could cause the breaker to trip as people would use them all.

I agree. If it were 20A radial, I don't think it would be good (or even necessarily 'competent') design practice for the designer to add sockets which he/she knew were likely to be used (possibly simultaneously) for two or more electric kettles.

If it were a 32A radial, then, of course, the situation would be no different from a 32A ring circuit. However, again, (although probably not the situation you have) if the designer believed that it was likely that more than two electric kettles would be used simultaneously, he/she should probably question the wisdom of having them all on the same 32A circuit.

Kind Regards, John

 

[AndyPRK]

If it’s a breaker it’s ok.
It’s not like a fuse will blow.

Anything is better than an extension lead

 

[JohnW2]

If it’s a breaker it’s ok. It’s not like a fuse will blow.

In pragmatic terms, that's true, but that doesn't make it any more correct a design practice to install a circuit which one knows is 'likely to be overloaded'. Don't forget that it requires 60A+ to trip a B32 in less than 10 minutes, so 4 or 5 3kW kettles all 'on' simultaneously might well not trip it.

Anything is better than an extension lead

Again, maybe pragmatically true but at least an extension lead will have a 13A fuse.

Kind Regards, John

 

[AndyPRK]

And how long does it take to blow a 13a fuse with 2 Kettles

 

[JohnW2]

And how long does it take to blow a 13a fuse with 2 Kettles

There's quite a large spread of characteristics - per the curves, at one extreme it could (assuming 3kW kettles) blow in under one second, but it could take as much as 6 minutes or thereabouts. I have no idea where 'typical' 13A BS 1362 fuses sit in that spectrum.

Kind Regards, John

 

[scousespark]

I know I could add a socket safely but if it is a radial on a 20a breaker I'd worry about adding any more sockets as they could cause the breaker to trip as people would use them all.

I assume the kettles are in use now, on an extension lead, and the breaker hasn’t tripped. Given the short time it takes t boil a kettle, I would take the view that adding sockets to 20a radial is low risk.

I’m concerned that you seem out of your depth here. Electrical installation is a bit more than odd job. You are not sure if you have a ring or radial, the number of cables in conduit, how to connect a spur to a ring. Are you aware of the tests you need to do? I’m not being clever here, just pointing out that this job seems to be a stretch for you.

 

[JohnW2]

I assume the kettles are in use now, on an extension lead, and the breaker hasn’t tripped. Given the short time it takes t boil a kettle, I would take the view that adding sockets to 20a radial is low risk.

Pragmatically, I would certainly agree.

However, pragmatism and 'correct design practice' do not necessarily coincide and, perhaps unusually (and perhaps because we are not talking about a domestic installation), I have been attempting the represent the latter. I would say that if a designer knows that it is 'likely' that two particular sockets will be used simultaneously to serve two 13A loads, that he/she should not really be party to putting both of those sockets on the same 20A circuit. Do you agree, or do you feel it's OK if (as in this case) the regulations are only likely be violated for short periods?

Kind Regards, John

 

[john4703]

I’m concerned that you seem out of your depth here. Electrical installation is a bit more than odd job. You are not sure if you have a ring or radial, the number of cables in conduit, how to connect a spur to a ring. Are you aware of the tests you need to do? I’m not being clever here, just pointing out that this job seems to be a stretch for you.

Thanks scousespark and I appreciate what you are saying. My main concern when I started this post was if it is OK to run both legs of a ring in one length of conduit, I can't think of a reason not to for a short run but I wondered if there was a reg that made it a no go. I'm guessing it is on a ring as I can see two T&E cables entering/leaving the existing socket. I will check it two ways: what size is the MCB? If it is 32A I'd guess it is a ring but it might not be as someone could easily have done something wrong in the past. I'd then turn off the MCB and RCD, remove the existing socket and check for continuity on all three wires. If it is a ring all should be continuous. If it is a radial they would not be. I'm getting old and it is a while since I served my time, 14th edition ruled then and I'd have been suggesting 7/.029 cable rather than 2.5mm.
I agree it is safe to fit as many sockets as you want to a 20A radial but I don't want phone calls to go and unlock the cupboard where the distributions board is to reset a breaker. I agree with the comments about the time it takes a fuse or breaker to open. It can take them a while to react to a reasonable overload.