Wiring multiple sockets on fused spur - what is the electrician calculating?

JohnW2 · 3 Oct 2019

Risteard said:
Presumably that is what he was suggesting, and it's a view I've heard expressed on numerous occasions. That doesn't make it a valid or correct view, however. In fact it can be beneficial to centre-feed e.g. to reduce the volt drop.

Indeed - as you say, it's really the antithesis of a 'correct' view - having branches in a radial will inevitably result in reduced voltage drop and EFLI at at least some, probably most/all, sockets - which can but be regarded as an advantage.

Kind Regards, John

securespark · 3 Oct 2019

JohnW2 said:
reduced......EFLI

Has he been on a diet?

AndyPRK · 3 Oct 2019

I'd get yourself another electrican.

He seams a jobs worth.

Justin0 · 3 Oct 2019

JohnW2 said:
Fair enough - that's not as bad as some, then! As flameport implies, it could well be that he has limited understanding of basic principles which would enable him to think a bit more laterally - so instead 'plays safe' by only doing things in the manner of 'examples' in the books etc. However, that means that he is being 'over-cautious', not in any way 'unsafe' in what he is saying.

So do you think the examples in the books don't include an FCU inline at the start of a spur rather than wired into the ring? Does anyone round here have access to some of these books?

JohnW2 · 3 Oct 2019

Justin0 said:
So do you think the examples in the books don't include an FCU inline at the start of a spur rather than wired into the ring?

No, 'the books' (even the 'guidance' examples in Appendices at the back of the Wiring Regulations) include that.

I think the comment related to 'branched radials' - probably just for simplicity, examples of radial circuits in books etc. often/usually don't have branches - which perhaps leads some people to believe that they never should have branches!

Kind Regards, John

Justin0 · 3 Oct 2019

Searching online I found this:

https://www.flameport.com/electric/socket_outlet_circuits/branch_tree.cs4

I assume that is the same flameport as on this thread?

"A new circuit should never be designed in this way, but alterations and additions to existing radial circuits can result in this type of arrangement."

So the electrician was right that it is at least undesirable?

JohnW2 · 3 Oct 2019

Justin0 said:
Searching online I found this: https://www.flameport.com/electric/socket_outlet_circuits/branch_tree.cs4 I assume that is the same flameport as on this thread?

Indeed so.

Justin0 said:
"A new circuit should never be designed in this way, but alterations and additions to existing radial circuits can result in this type of arrangement." So the electrician was right that it is at least undesirable?

That is, indeed, what flameport seems to be saying there, but I don't really understand why. He goes on to say:

flameport (on his website) said:
The main problem here is that it is difficult to identify which socket outlet represents the end of the circuit - this example has three 'ends'. Some socket outlets have two cables, some have one and some have three.

True though that is, I don't understand why one would need to ascertain (or care about) which socket "is the end of the circuit" (other that for the purpose of testing) - particularly given that there is actually no single 'end'. Maybe he's just thinking of testing - in which there is a need to ascertain the voltage drop and EFLI at the socket most distant from the CU?

@flameport : can you explain your thinking, please? Is it just about testing?

As I recently wrote, having a branched radial will nearly always result in lower voltage drops and loop impedance than the corresponding radial without branches - and I would personally consider that to be a (functional) advantage, not (functionally) 'undesirable'.

Kind Regards, John

Risteard · 3 Oct 2019

Justin0 said:
It's a shame because he states on his card he is an NIC EIC approved contractor, he seems a nice guy and I don't get the impression he's trying to rip me off (he's not asking for extra payment for this). It's also not as though he's being a cowboy and trying to do something unsafe.

What I don't understand is that if you are wiring this installation, what has this contractor got to do with it? What is his involvement and why is he advising you?

sparkwright · 3 Oct 2019

John - Testing and fault finding I would guess, but don't really know what the fuss is about.

I would sometimes do a branch on a new radial circuit - the cable going to a bathroom shaver socket on a lighting circuit being the most obvious example I suppose.

JohnW2 · 3 Oct 2019

sparkwright said:
John - Testing and fault finding I would guess, but don't really know what the fuss is about.

As I said, that's all I can think of - but I wouldn't personally regard that as a reason fro calling a branched radial 'undesirable', particularly given that (as I explained) I think that (electrically speaking) it is in some senses 'better' than a non-branching one.

sparkwright said:
I would sometimes do a branch on a new radial circuit - the cable going to a bathroom shaver socket on a lighting circuit being the most obvious example I suppose.

Indeed - and, in fact, many lighting circuits themselves (i.e. the connections to the lights) are often most sensibly (and 'efficiently') done with branches.

Kind Regards, John

JohnW2 · 3 Oct 2019

Risteard said:
What I don't understand is that if you are wiring this installation, what has this contractor got to do with it? What is his involvement and why is he advising you?

It sounds as if the OP asked an 'electrician' to check 'what he had done' (or intended to do) - but, in view of what this 'electrician' then said, perhaps now regrets that he did ask!

Kind Regards, John

Justin0 · 3 Oct 2019

Risteard said:
What I don't understand is that if you are wiring this installation, what has this contractor got to do with it? What is his involvement and why is he advising you?

It's a good question. The answer is that I originally got him in to put a socket in the garden, because I understand that is "Part P" work.

This would connect inside the garage. So he needs to be happy with the wiring in the garage before he does the installation.

JohnW2 · 3 Oct 2019

Justin0 said:
It's a good question. The answer is that I originally got him in to put a socket in the garden, because I understand that is "Part P" work.

If you mean 'notifiable work', that is no longer the case in England (although it remains the case in Wales), assuming that it is not a 'new circuit' (from the house CU).

Kind Regards, John

flameport · 3 Oct 2019

JohnW2 said:
@flameport : can you explain your thinking, please? Is it just about testing?

A circuit arrangement with multiple branches, junction boxes, sockets with multiple cables, etc. will work and could be safe.
Determining where the cables are for testing, fault finding or just to determine what type of circuit it is would be rather time consuming and tiresome.
Designing and installing a new circuit that way would be an exercise in wasting everyone's time.

JohnW2 · 3 Oct 2019

flameport said:
A circuit arrangement with multiple branches, junction boxes, sockets with multiple cables, etc. will work and could be safe.

I can't disagree that 'unnecessary' (which is virtually always the case in terms of 'new wiring') JBs are 'undesirable', but I'm not sure that 'sockets with multiple cables' (not commonly more than 3) are much of an issue...

flameport said:
Determining where the cables are for testing, fault finding or just to determine what type of circuit it is would be rather time consuming and tiresome.

I suppose it's a matter of opinion,

I'm not particularly convinced that it's necessarily any more difficult to identify the socket which is 'furthest from the CU', or 'where the cables are', in a branching radial than in a ring final (particularly if the latter has spurs), and 'the type of circuit' (at least, 'ring or radial') can, if necessary, be rapidly determined by looking in the CU.

In any event, as I said, I think that those ('convenience') issues have to be balanced against the (admittedly small) theoretical electrical 'advantages' of having branched radials. I have to say that, personally, I'm fairly neutral on the issue. I would install a non-branching radial if that were reasonable and convenient, but would not hesitate to have branches if that were more convenient. As I said, it's 'everyone to their own', I suppose.

Kind Regards, John

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Wiring multiple sockets on fused spur - what is the electrician calculating?

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