Installing extra appliance, electric supply advice needed

[JohnW2]

Yes, I know all that but you are introducing red herrings.

Hmmm. I was merely responding to the concept ('red herring'?) you introduced of 2 x 2.5mm² cables being equivalent to 1 x 5mm², wasn't I?

No one would query two 2.5mm² from close points on the ring; you have suggested two spurs from the same point.

As you know, some people do query that - but, as you say, not me.

Because there is conduit in place I have proposed 4mm² and, even though you actually agree, we have ended up having a prolonged discussion although it was BAS who disagreed and it was to him that my justification was aimed.

I agreed that it was electrically OK (as OK as two 2.5mm² cables attached close, or at the same point, to the ring) - but, when I first commented, I did add that there was going to be debate about whether that re-compliant (which is when BAS jumped in and said that there was no scope for debate, because it was non-compliant!)

There is no doubt that my proposal is electrically safe.

I think that we (including BAS) are all agreed on that.

The debate concerns whether the regulations allow it or not because they do not expressly show it - but then - nor do they expressly forbid it.

That, coupled with the fact that it is clearly electrically OK (as above, as OK as 2x2.5mm² 'close spurs') is the basis on which I personally believe that it can be said to be regs-compliant - but, as you say, that is the debate, and there are clearly some (and probably not just BAS) who disagree.

Kind Regards, John ²

 

[ban-all-sheds]

Ah, the selective diversity rule is applied !

What is the rule for washing machines and tumble driers?

 

[JohnW2]

Ah, the selective diversity rule is applied !

I don't think it's really 'selective diversity'. At least as far as I am concerned, the main reason I feel the need to express caution is that a good few electricians appear to report, on the basis of their experiences, that sockets and/or plugs have suffered when a WM and TD have been run off the same double socket.

I have no personal experience of that. Until a few years ago, I had lived for years with a situation in which the two machines, often running simultaneously, were run off one double socket. Plugs and socket got pretty warm at times, but never suffered any obvious damage.

Kind Regards, John

 

[deadshort]

Well BAS according to you it is not allowed

I would also totally disagree with the 2 single sockets as 2 spurs from the same point on the ring using two cables to do so. But that's just me !


Regards,

DS

 

[JohnW2]

I would also totally disagree with the 2 single sockets as 2 spurs from the same point on the ring using two cables to do so. But that's just me !

As a matter of interest, where do you draw the line? Would you be happy if the two spurs originated from sockets/accessories/JBs which were 100mm apart? 250mm apart, 500mm apart, 1m apart, 2m apart ... or what? I presume that you don't approve of the grid switch setups which are quite common in kitchens?

If it's 'unbalancing the ring' that worries you, once you have got more than about quarter or so (IIRC - I have the sums somewhere!) of the way (from CU) down one leg of the ring, it's impossible to overload any of the cable even if the entire 30/32A load is applied at one point.

Kind Regards, John

 

[deadshort]

4x 2.5 cables in to the back of a socket is a no no from me.
It's all to do with standards of workmanship and not hypothetical theory or being a smart ar….


Kind regards,

DS

 

[JohnW2]

4x 2.5 cables in to the back of a socket is a no no from me. ... It's all to do with standards of workmanship and not hypothetical theory or being a smart ar….

Oh, I see - that's fair enough. I'm used to people raising the 'point loading of the ring' argument. So do I take it you're happy to have separate spurs originating from immediately adjacent sockets on a ring, or from adjacent DP grid switches on a ring?

Kind Regards, John

 

[aesmith]

MK double sockets are rated for 20A total, I don't know if other manufacturers are similar.

 

[JohnW2]

MK double sockets are rated for 20A total, I don't know if other manufacturers are similar.

We've had this discussion countless times before, and the truth is very difficult to ascertain (and my conversation with the MK techies didn't help much). Many, perhaps most, people seem to think that 20A is probably the 'maximum' for most double sockets, but some think it's 13A and a few think it's 26A. Many double sockets have "13A" embossed on the back, which doesn't help the confusion. However, as I've said, one hears a good few reports of plugs/sockets suffering when two heavy loads have been supplied by one double socket.

The guidance in the regs regarding ring final circuits (Appendix 15) allows for a double socket on an unfused spur to be supplied by a cable of CCC no more than 20A (per 433.1.103), perhaps implying that whoever wrote that believed that a double socket represented a maximum load of 20A.

Kind Regards, John

 

[EFLImpudence]

The guidance in the regs regarding ring final circuits (Appendix 15) allows for a double socket on an unfused spur to be supplied by a cable of CCC no more than 20A (per 433.1.103), perhaps implying that whoever wrote that believed that a double socket represented a maximum load of 20A.

I presume you meant to write 'no less than 20A'?

Therefore I am a bit confused about what you mean because Appendix 15 makes no mention of that and ...

the reference to 20A minimum in 433.1.103 refers to the circuit - the ring; it does not consider spurs - and this is after stating a minimum csa of 2.5mm² (except MICC).

 

[JohnW2]

The guidance in the regs regarding ring final circuits (Appendix 15) allows for a double socket on an unfused spur to be supplied by a cable of CCC no more than 20A (per 433.1.103), perhaps implying that whoever wrote that believed that a double socket represented a maximum load of 20A.

I presume you meant to write 'no less than 20A'?

No. I suppose that it's another of those 'language issues'. I meant what I wrote - that 433.1.103 allows a ring final to use a cable with a CCC which is "no more than 20A" (i.e. which is "as low as 20A").

Therefore I am a bit confused about what you mean because Appendix 15 makes no mention of that and ... the reference to 20A minimum in 433.1.103 refers to the circuit - the ring; it does not consider spurs - and this is after stating a minimum csa of 2.5mm² (except MICC).

I think you are probably trying to 'split hairs'. 433.1.103 starts by saying that it is talking about a "ring final circuit, with or without unfused spurs" and then goes on to say that "the circuit" should be wired in cable with a CSA of at least 2.5mm² (unless MICC) and a CCC of no less than 20A. I personally think that it is reasonable to assume that those CSA/CCC requirements relate to unfused spurs as well as the ring itself.

However, if you reject that viewpoint, and take the view that the regs (and App 15) are 'silent' about the required CCC of spur cables, then it actually gets 'worse' - since, with the most extreme of installation methods, the CCC of 2.5mm² T+E could be as low as 13.5A.

Kind Regards, John

 

[EFLImpudence]

No. I suppose that it's another of those 'language issues'. I meant what I wrote - that 433.1.103 allows a ring final to use a cable with a CCC which is "no more than 20A" (i.e. which is "as low as 20A").

Ah, right.
In that case - yes but there are two.

I think you are probably trying to 'split hairs'. 433.1.103 starts by saying that it is talking about a "ring final circuit, with or without unfused spurs" and then goes on to say that "the circuit" should be wired in cable with a CSA of at least 2.5mm² (unless MICC) and a CCC of no less than 20A. I personally think that it is reasonable to assume that those CSA/CCC requirements relate to unfused spurs as well as the ring itself.

Or you (I) could say the spurs are irrelevant to these requirements.

However, if you reject that viewpoint, and take the view that the regs (and App 15) are 'silent' about the required CCC of spur cables, then it actually gets 'worse' - since, with the most extreme of installation methods, the CCC of 2.5mm² T+E could be as low as 13.5A.

Well, yes but the installation method applies to all conductors.
That, surely is the point of stating the minimum CCC of 20A.

What do you think is the reason for NOT allowing a 1.5mm² spur feeding a single socket?

 

[JohnW2]

I think you are probably trying to 'split hairs'. 433.1.103 starts by saying that it is talking about a "ring final circuit, with or without unfused spurs" and then goes on to say that "the circuit" should be wired in cable with a CSA of at least 2.5mm² (unless MICC) and a CCC of no less than 20A. I personally think that it is reasonable to assume that those CSA/CCC requirements relate to unfused spurs as well as the ring itself.

Or you (I) could say the spurs are irrelevant to these requirements.

One could say that. However, the requirements relate to 'the circuit' and I would have thought that most people (even the BS7671 definition!) would say that spurs were part of 'the circuit'. wouldn't they?

However, if you reject that viewpoint, and take the view that the regs (and App 15) are 'silent' about the required CCC of spur cables, then it actually gets 'worse' - since, with the most extreme of installation methods, the CCC of 2.5mm² T+E could be as low as 13.5A.

Well, yes but the installation method applies to all conductors. That, surely is the point of stating the minimum CCC of 20A.

Indeed - but we're talking about the spur cable, and you don't seem to think that the 20A minimum (as stated in 433.1.103) applies to that.

What do you think is the reason for NOT allowing a 1.5mm² spur feeding a single socket?

No electrical reason, really (given the downstream ≤13A fuse in the plug) - so maybe this is another example of a 'lack of exhaustiveness' in Appendix 15. I would personally be happy with it. Maybe the reason it's not included in App 15 (whereas a 1.5mm² fused spur is) is because of a fear that some people might mis-read/misinterpret it as allowing a double socket on an unfused spur to be fed with 1.5mm²?

Kind Regards, John

 

[EFLImpudence]

One could say that. However, the requirements relate to 'the circuit' and I would have thought that most people (even the BS7671 definition!) would say that spurs were part of 'the circuit'. wouldn't they?

Spurs are obviously part of the circuit but not part of the ring.
Does the wording not say that "ring circuits must be done like {the following} whether or not there are spurs".
I cannot see why the spurs, especially the without spurs part, are mentioned at all.

Indeed - but we're talking about the spur cable, and you don't seem to think that the 20A minimum (as stated in 433.1.103) applies to that.

There is no reason for it to apply to the spurs (especially if there aren't any), is there?

No electrical reason, really (given the downstream ≤13A fuse in the plug) - so maybe this is another example of a 'lack of exhaustiveness' in Appendix 15. I would personally be happy with it. Maybe the reason it's not included in App 15 (whereas a 1.5mm² fused spur is) is because of a fear that some people might mis-read/misinterpret it as allowing a double socket on an unfused spur to be fed with 1.5mm²?

I suppose not every option can be shown but a noted box, as with the other options, could be included.

 

[EFLImpudence]

Quote instead of edit, again.