I'm confused about junction box rules

JohnW2 · 16 Oct 2025

SUNRAY said:
Are you saying a DSSO on a 32A radial cannot be done with 2.5mm²? ... I believe we have established several times that it is permissible

No, you are 'over-interpreting' what I wrote. As you say, what you describe is not only permissible, but it's actually one of the things which IS shown in Appendix 15 - but there then are 'restrictions', in that one could not power further sockets (or anything else) through that same 2.5 mm² cable.

In contrast, in what I previously wrote, I meant exactly what I did write - that IF everything is done in the same size cable (e.g. 4 mm² for a 32A radial or 2.5 mm² for a 32A ring final) then there are no such restrictions' with a radial, but there are with a ring final.

By analogy with what you suggest for a radial, I can't see that there would be any (electrical) problem with a 1.5 mm² unfused spur from a 32 A ring final feeding one single socket - but that's certainly not something you'll find suggested in App 15

trojanhawrs · 16 Oct 2025

PotatoSoup said:
Thank you

I hope he's not my electrician!!

Thank you

It would probably be an overreaction just because of the junction box but I'd like my electrics checked anyway to make sure all of them are ok (not just to check this chap's work) but this has made me prioritise getting a check up while everything is accessible rather than it being something I leave on my "to do down the line" list. My guess would be that everything else he's done will be absolutely fine. As someone said, the junction box is probably safe - just not regulation. Also - this is probably a silly thing to base anything on but it's in my head - this electrician is definitely a perfectionist normally. The way he aligned the wires coming out of the consumer unit was a work of art!! It was honestly soothing to watch him work lol. And he's clearly intelligent. It's why I came on here to check if there was something I was missing because he just didn't seem the type of person to fumble. But, I'm not an electrician, so for all I know he's made loads of mistakes and I'm just blissfully unaware.

Thanks so much - I appreciate it I'll go find another electrician.

Sorry, last question on this, which professional body is the best one to look for when searching for an electrician, please?

It might be he didn't properly take in the fact you're plastering it, it might be that maintenance free JBs can be awkward to use depending on the existing cable you've got and the reality is if someone gives it a tug the screws are a lot more likely to hold than plastic cable grips and some wagos.
I personally wouldn't worry about it, if the light stops working you can call him back.

SUNRAY · 17 Oct 2025

JohnW2 said:
No, you are 'over-interpreting' what I wrote. As you say, what you describe is not only permissible, but it's actually one of the things which IS shown in Appendix 15 - but there then are 'restrictions', in that one could not power further sockets (or anything else) through that same 2.5 mm² cable.

In contrast, in what I previously wrote, I meant exactly what I did write - that IF everything is done in the same size cable (e.g. 4 mm² for a 32A radial or 2.5 mm² for a 32A ring final) then there are no such restrictions' with a radial, but there are with a ring final.

By analogy with what you suggest for a radial, I can't see that there would be any (electrical) problem with a 1.5 mm² unfused spur from a 32 A ring final feeding one single socket - but that's certainly not something you'll find suggested in App 15

It can be tricky to to follow the intended meaning of a comment sometimes. But that clarifies it.
As I wrote before; basically the rules for spurs on the two circuit types are essentially the same. That doesn't mean I like all of the rules though

JohnW2 · 17 Oct 2025

SUNRAY said:
It can be tricky to to follow the intended meaning of a comment sometimes. But that clarifies it.

Yes, it can be very difficult, but I'm glad you now understand what I meant!

SUNRAY said:
As I wrote before; basically the rules for spurs on the two circuit types are essentially the same.

Yes, they're the same in the sense that a 2.5² mm 'spur' (or branch) from a 32A circuit can only support one (single or double) socket regardless of whether it is a radial or ring final circuit [that being because cable protection derives from the downstream fuse(s) in plug(s) (or FCU). ]. The 'difference' which may cause confusion for some people is that that 2.5 mm² spur is the same size cable as the main part of the circuit for a ring, but smaller than the cable in the main part of the circuit in the case of a 32A radial.

Another difference, which again can cause confusion, is that a spur (which has the 'load restrictions') from a ring is obvious from the topology, whereas that is not the case with a radial - with a radial there are only load restrictions on a branch if its cable is smaller than that of the rest of the circuit (which is why I personally use the term 'branch' for an equal-size branch in a radial, but call it a 'spur' if it is reduced in cable size).

ebee · 17 Oct 2025

blup said:
I note you are referring to bad practices now rather than breach of the regulations.

I'm not sure what sort of wriggling that is meant to represent, but I use wording fairly loosely and on the occasion the reason for the 'bad practice' is that it represented 'a breach of the regulations'.

The most powerful reg in the book is ???
Hint - around about reg no Regulation 421.1 as your starter for 10!

If some tradesman is doing a paying job for a paying customer then he is obliged to use reasonable skill and care, that would include doing any wiring to BS7671 (or a sufficient standard - including one of a "civilised" country or something.) you would not be compliant with something you could not be able to stand up in court to defend. BS 7671 is not the law in itself, but it would usually be extremely unwise not to treat it as if it the actual law!

securespark · 17 Oct 2025

EFLImpudence said:
However two sockets, or possibly more, each on its own spur cable - spurred from a single point - is still allowed.

I have never thought this was a good idea.

Think about the loading of a ring final, where you may have two or three sockets close to each other, each drawing a heavy load.

To my mind, the scenario is made better by connecting the loads across a few sockets wired on the ring final circuit, rather than all connected to the same single point on the circuit.

Having had discussions with Paul Cook (IEE) about this in the distant past, he was very much in agreement.

If I were wiring a house today, I wouldn't even entertain using ring finals for sockets. I'd just use 20A radials and possibly a 32A radial for the kitchen.

Now, I know that could spawn a whole thread's worth of responses...!

blup · 17 Oct 2025

ebee said:
I'm not sure what sort of wriggling that is meant to represent, but I use wording fairly loosely and on the occasion the reason for the 'bad practice' is that it represented 'a breach of the regulations'.

Work can comply with tne regulations but still be bad practice eg quality of thd installation. A poorly installed mf jb can create problems regardless of whether it’s accessible or not. It may not be picked up at all on an EICR.

ebee said:
The most powerful reg in the book is ???
Hint - around about reg no Regulation 421.1 as your starter for 10!

The regs refer to non combustible rather than a metal surround, is it bad practice to come up with a workable alternative?

ebee said:
If some tradesman is doing a paying job for a paying customer then he is obliged to use reasonable skill and care, that would include doing any wiring to BS7671 (or a sufficient standard - including one of a "civilised" country or something.) you would not be compliant with something you could not be able to stand up in court to defend. BS 7671 is not the law in itself, but it would usually be extremely unwise not to treat it as if it the actual law!

I agree as a general rule, which is why I suggested that the use of a single piece of plasterboard would be a suitable exception to the regs.

SUNRAY · 17 Oct 2025

securespark said:
securespark said:

EFLImpudence said:

...However two sockets, or possibly more, each on its own spur cable - spurred from a single point - is still allowed.

Click to expand...

I have never thought this was a good idea...

Click to expand...

It's no different to having the additional sockets as part of the ring, in which case the number of sockets is unlimited

However yes I am very aware of the problems with heavy loads at a single point, example https://www.diynot.com/diy/threads/...s-is-this-good-pic.483672/page-9#post-3927729 #124

EFLImpudence · 17 Oct 2025

securespark said:
I have never thought this was a good idea.

Nevertheless.

securespark said:
Having had discussions with Paul Cook (IEE) about this in the distant past, he was very much in agreement.

Perhaps you have discovered the cause of the poor(wrong) guidance.

JohnW2 · 17 Oct 2025

securespark said:
EFLImpudence said:

However two sockets, or possibly more, each on its own spur cable - spurred from a single point - is still allowed.

Click to expand...

I have never thought this was a good idea. ... Think about the loading of a ring final, where you may have two or three sockets close to each other, each drawing a heavy load. ....To my mind, the scenario is made better by connecting the loads across a few sockets wired on the ring final circuit, rather than all connected to the same single point on the circuit. Having had discussions with Paul Cook (IEE) about this in the distant past, he was very much in agreement.

He, and anyone else who understands the principles, should understand that potential overloading of parts of the cable of a ring final has got absolutely nothing to do with the number and size of loads connected at a single 'point' but, rather, depends entirely on where the 'points' are on the ring.

A potential (in practice, very rare) problem only arises if a lot of loads are connected close to one end of the ring. In fact, the very best scenario of all (from the POV of cable loading) is to have ALL of the loads connected at a single 'point', that point being the mid-point of a ring.

Many people don't seem to think very straight about any of this. The same people who are unhappy with two or three spurs being connected to a ring at one 'point' (e.g. socket) seem happy with, say, one spur coming from each of three sockets which are only an inch or two apart. Similarly, we only really hear people discussing this issue in relation to spurs, whereas exactly the same considerations (and potential 'concerns') apply to the location of sockets on a ring (i.e. it's theoretically not desirable to have a lot of sockets close to one end of the ring.

JohnW2 · 17 Oct 2025

blup said:
Work can comply with tne regulations but still be bad practice eg quality of thd installation. A poorly installed mf jb can create problems regardless of whether it’s accessible or not.

Very true. The converse is also true - that an installation which has been immaculately executed (which some would call 'good workmanship/practice') may be non-compliant (e.g. excellently installed wiring, but which used undersized cable.
However, as I wrote, when talking about a paid professional electrician, I would say that 'good practice' had to start with compliance with relevant rules/regulations (and then also be 'good' in its execution).

blup said:
The regs refer to non combustible rather than a metal surround, is it bad practice to come up with a workable alternative?

As above, I think that 'good practice' on the part of a professional electrician must start with compliance with relevant regs. However, as you imply, BS7671 does not insist on a metal CU (only a 'non-combustible' one, however you choose to interpret that), so there is scope for a 'workable alternative' to be compliant. More generally, BS 7671 says that alternatives to what is required by its regulations are always acceptable IF one can demonstrate/prove (very difficult for most people) that the result is no less safe than would be the case with strict compliance with the regs.

blup said:
I agree as a general rule, which is why I suggested that the use of a single piece of plasterboard would be a suitable exception to the regs.

If the electrician were going to install the ceiling, then, yes, he could have created a 'removable panel'. However, that was not the situation, and we are told that the electrician was aware of the fact that a (not 'removable') ceiling was going to be installed by the OP.

JohnW2 · 17 Oct 2025

ebee said:
If some tradesman is doing a paying job for a paying customer then he is obliged to use reasonable skill and care, that would include doing any wiring to BS7671 (or a sufficient standard - including one of a "civilised" country or something.) you would not be compliant with something you could not be able to stand up in court to defend. BS 7671 is not the law in itself, but it would usually be extremely unwise not to treat it as if it the actual law!

Quite so - that's exactly what I've been saying - that, although 'good workmanship/good practice' on the part of a professional electrician involves a lot more than just this, I believe it has to start with compliance with relevant rules, regulations and laws.

Kind Regards, John

JohnW2 · 17 Oct 2025

SUNRAY said:
However yes I am very aware of the problems with heavy loads at a single point ...

As I've just written, that us only a potential issue if the 'single point' is fairly close to one end of the ring. As I also wrote, the very best situation (for the cable) is to have ALL loads connected at a 'single point' (the mid-point of the ring).

ebee · 17 Oct 2025

A good approximation to start with is
A/ loads divided equally fairly equally around to ring and avoiding unequal loading of the two legs.
or
B/ Most loading centred around the midpoint - the middle one thiird of the ring length would usually be considerd acceptable
or
C/ Combining A/ and B/ above.

Note - Loads divided equally not just as required but also giving due consideration to likely duration.
"bag of a fag packet" is usually quite acceptable rather than reams and reams of Precise calculations.

No AMPS or VOLTS were harmed during the making of this statement!

securespark · 17 Oct 2025

JohnW2 said:
As I've just written, that us only a potential issue if the 'single point' is fairly close to one end of the ring. As I also wrote, the very best situation (for the cable) is to have ALL loads connected at a 'single point' (the mid-point of the ring).

The single point I was talking about here was literally that: multiple spurs being taken from the same single point on a ring final.

Your single point scenario is not quite that.

Further, the very best situation of which you speak often does not happen.

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I'm confused about junction box rules

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