Spurs off spurs and the Regulations

[ericmark]

The problem is with a 20 amp radial we can spur off as many times as we want with out breaking any rules and to tell the DIY guy you can't have a unfused spur from an unfused spur is wrong.

We need to tell him/her that (per Appendix 15) they can't have a fused spur from an unfused spur as well. However, because of what you say, we should perhaps be clearer in what we tell a DIYer - namely that all this talk about 'spurs from spurs' relates specifically to spurs from a 30/32A ring final circuit.

Kind Regards, John

You as so often are spot on with that. What I think we need is a well written guide which we can either copy and paste or link to as this comes up so often. Being dyslexic clearly not a job for me.

 

[JohnW2]

We need to tell him/her that (per Appendix 15) they can't have a fused spur from an unfused spur as well. However, because of what you say, we should perhaps be clearer in what we tell a DIYer - namely that all this talk about 'spurs from spurs' relates specifically to spurs from a 30/32A ring final circuit.

You as so often are spot on with that. What I think we need is a well written guide which we can either copy and paste or link to as this comes up so often. Being dyslexic clearly not a job for me.

Few things are simple! One very common problem is that those who ask questions here often do not know (at all, or for certain) whether they have a ring final or radial circuit and, if the former, whether a particular socket is part of the ring, a fused spr or an unfused spur. Explaining to them how to (safely) ascertain that is far from easy - and if they cannot find out for certain what they are dealing with, then there's obviously little point in telling them that comments only relate to 'spurs from spurs on a 30/32A ring final circuit.

Kind Regards, John

 

[ban-all-sheds]

It would help if "spur" was only used in the special sense of a branch from a ring final, i.e. radials never have spurs, they only have branches.

Like it was before the 17th.

The argument about how many things on an unfused spur is pretty simple to distill. An accessory on a spur is no longer being supplied by a ring final, so you need to consider the overload/fault protection of its cable just as you would any other circuit, so for example, a 2.5mm² cable on a 32A breaker is going to have to rely on the nature of the load for its overload protection, hence only one socket outlet. One socket outlet + one shaver socket is also OK for the load limiting by characteristic. As would be 100 shaver sockets, I shouldn't wonder.

So there's that, and bewaring the fact that you need to consider the ring up to the spur point as a parallel circuit.

 

[JohnW2]

It would help if "spur" was only used in the special sense of a branch from a ring final, i.e. radials never have spurs, they only have branches. Like it was before the 17th.

Personally, the terminology I use (which appears to be the same in current regs, certainly in Appendix 15) is that, for either a ring final or radial circuit, a 'spur' is a reduced-CSA branch. Hence, I would call any ≥4mm² branch of a 4mm² radial just a branch, but I would call a 1.5mm² or 2.5mm² emination from a 4mm² radial 'a spur'. Conversely, if it were ever done, I suppose I wouldn't consider an ≥5mm² emination from a 2.5mm² ring final as a 'spur' (indeed, although stretching my definition, I might well not consider a 4mm² one as a spur). I think such terminolgy reflects the crucial issues and therefore underlines what you go on to say....

The argument about how many things on an unfused spur is pretty simple to distill. An accessory on a spur is no longer being supplied by a ring final, so you need to consider the overload/fault protection of its cable just as you would any other circuit, so for example, a 2.5mm² cable on a 32A breaker is going to have to rely on the nature of the load for its overload protection, hence only one socket outlet. One socket outlet + one shaver socket is also OK for the load limiting by characteristic. As would be 100 shaver sockets, I shouldn't wonder. So there's that, and bewaring the fact that you need to consider the ring up to the spur point as a parallel circuit.

Yep, I agree with all that. However, as we know, those who are totally married not only to 'the regs', but even to an 'informative' Appendix of the regs, are likely to be unhappy with a lot of that - "if it's not in App 15, or contravenes what App 15 says, then it must be forbidden".

Kind Regards, John

 

[ban-all-sheds]

And those who cannot think are destined to be soft robots, not knowledge workers.

 

[JohnW2]

And those who cannot think are destined to be soft robots, not knowledge workers.

No argument with that.

Kind Regards, John

 

[securespark]

Kidn Regards, John

Yuor singnature's gnoe all wrong.

You should be very familiar by now with the 'adjacent character transpositions' that result from my high-speed two-finger typing I detect and correct a lot of them, but some get through -particularly 'obvioulsy', which I do so often that it's almost starting to 'look right' to me!

Kind Regards,Jophn

If you make it your sig, it will be added automatically to every post you make.

It is interesting to see the old regulations again

My pleasure!!

 

[ericmark]

A spur is a short appendix to the leg does not really matter if referring to horse riding, or cock fighting. And for the non electrician we have to expect them to see it that way.

Personally I would have called a fused spur a radial it is a circuit in it's self not just an appendix to an existing circuit and does not need to be short however the 17th has called them spurs so we have to accept the phrase fused spur.

I see the point that DIY people may not understand what they are working on but if we were to tell all DIY people what the rules are then they simply can't work on the electrics as they will not have the required test equipment.

So looking for a short statement which captures the essence of the rules. So I will try and get the ball rolling and this is what I feel encompasses the rules.

A 2.5mm² un-fused spur from a supply protected with a 30/32 amp fuse/MCB/RCBO should not exceed 3 meters in length and should supply only one device which either contains a fuse or can only be used with a plug which contains a fuse.

I am sure there is something I have overlooked but that's the whole point of a forum so others can highlight my errors.

Should we include

(ii) be installed in such a manner as to reduce the risk of fault to a minimum, and
NOTE: This condition may be obtained. for example, by reinforcing the protection of the wiring against external influences
(iii) be installed in such a manner as to reduce to a minimum the risk of fire or danger to persons.

I think that over complicates the answer and would not bother including but I will be interested what other think.

 

[JohnW2]

If you make it your sig, it will be added automatically to every post you make.

Indeed, but it would then always be exactly the same, with no typos - much less fun! It would also have an annoying line above it - fine if the 'signature' is actually a 'footnote' ('quote of the week', or whatever), much more odd if it really is a 'signature'

Kind Regards, John

 

[JohnW2]

So looking for a short statement which captures the essence of the rules. So I will try and get the ball rolling and this is what I feel encompasses the rules.

A 2.5mm² un-fused spur from a supply protected with a 30/32 amp fuse/MCB/RCBO should not exceed 3 meters in length and should supply only one device which either contains a fuse or can only be used with a plug which contains a fuse.

I am sure there is something I have overlooked but that's the whole point of a forum so others can highlight my errors.

Although it seems very logical that it should, I'm not even sure that 433.1.103 (which 'authorises' riing final circuits, and spurs therefrom) intends that the "3m rule" (with its conditions) of 433.2.2 should apply to unfused spurs from ring finals. The only specific guidance about the length of unfused spurs from ring finals comes from the OSG, which says:

As a rule of thumb for rings, unfused spur lengths should not exceed 1/8 the cable length from the spur to the furthest point of the ring

Goodness knows how they came up with that, but that's what it says!

Kind Regards, John

 

[ericmark]

It is possible that 434.5.2 will mean the 3 meter rule will not apply but reading 434.5.2 I can't see any DIY guy understanding the calculations given.

I do have issues with some of the suggestions given in the OSG but mine is pre-17th edition.

So now 106 meters max due to volt drop changes and use of RCD on all sockets but clearly in the centre of a 106 meter ring the length of a spur is zero but from the CU then around 30 meters before the volt drop is exceeded and I would think the 1/6th rule of thumb was designed to allow for the different lengths before volt drop is exceeded I use excel to work it out but to be frank can't see any DIY guy working it out!

So in real terms we know 1.44 ohms is the limit and we plug in the loop impedance meter and see if there is any spare capacity before adding a spur. So how can we expect a DIY guy to do that or understand that the max length will depend on how close he is to the consumer unit?

At least adopting the 3 meter rule you have something the DIY man can understand even if clearly a spur is taken from the centre of a 106 meter ring it would not comply.

The bit I missed is the RCD protection so a new un-fused spur can only be taken from a ring already protected by a RCD unless special cable or surface cable is used and the socket has a built in RCD.

Once we look at pre-2008 installations then we have many more questions for example does the max ring length drop back to 88 meters?

We all know before we extend a circuit we need the loop meter, the RCD tester and the insulation tester all which the DIY guy will not have. I was trying to reduce the information to a simple statement but clearly that's not really possible.

 

[mfarrow]

Wow, I was really just after some historic context to how the regulation disappeared, but I'm glad I ported this discussion out of the poor man's shaver socket discussion now!

What I was expecting, and tried to invoke a response on, was what the electrician's 'clubs' say about this, in terms of how the regulations would apply and what sort of EICR codes would be given. I agree that from an engineering perspective, there's very little argument to be had that a few milliamps isn't going to break the cable, even 1mm *might* be OK, however because there are so many 'robotic' electricians out there, I would sooner avoid the inevitable debate with both the electrician and his club's representatives (who often don't agree between themselves!) at EICR time, and I'd sooner have no codes if I'm trying to sell the house.

 

[JohnW2]

What I was expecting, and tried to invoke a response on, was what the electrician's 'clubs' say about this, in terms of how the regulations would apply and what sort of EICR codes would be given.

That's an interesting way of looking at it. When it comes to 'EICR codes', I think that the person creating them has to be at least prepared to cite the specific regulations with which the installation is non compliant. They therefore might struggle to 'code' many of the things we're talking about since, no matter what they may feel, they are probably only addressed by guidelines (Appendix 15 of regs and OSG), not by any specific 'required' regulations of BS7671.

I agree that from an engineering perspective, there's very little argument to be had that a few milliamps isn't going to break the cable, even 1mm *might* be OK,...

Just for completeness, unless we are talking about 'lighting', the regs require a minimum of 1.5mm².

... however because there are so many 'robotic' electricians out there, I would sooner avoid the inevitable debate with both the electrician and his club's representatives (who often don't agree between themselves!) at EICR time, and I'd sooner have no codes if I'm trying to sell the house.

I can understand that - but it is probably some of those very same 'robotic' electricians who, particularly if 'challenged', would be reluctant to code anything if they could not find a specific regulation to cite.

Kind Regards, John

 

[mfarrow]

When it comes to 'EICR codes', I think that the person creating them has to be at least prepared to cite the specific regulations with which the installation is non compliant.

They certainly do, and if we look at the BRB (sorry BGB's at work and BSOL is offline) then 433.1.5 would be the one they'd cite. This exempts all-BS 1363 accessories on British ring finals from the overload regulations, and regulates this at the same time with certain conditions, which we all know off by heart now. As soon as you add a non-BS 1363 accessory have you made the ring circuit non-compliant? Is that a code 2, or a code 3? What is best practise for this? Where is it published? What if I used 1mm² cable? It's such a complicated paragraph, that can be read in so many different ways.

When it comes to an EICR, which I may or may not have requested as a vendor/client, I'd sooner discuss regulations that are clear, but seemingly ambiguous to others:

- Single phase MCBs on 3-phase, 4-wire lighting circuits. Allowed with an isolator and safer than a 3-phase MCB.
- Bonding everything in bathrooms (had that argument in the pub the other night). Not needed.
- Double/reinforced only circuits (OK so 412.1.3 makes this a bit more contentious, as there is no definition of 'user' in the regulations). The future, IMHO.

Or the regulations that don't actually exist, but people think exist:

- ring finals only being allowed if they're ones mentioned in 433.1.5.
- Joints in main protective bonding conductors. Not regulated by BS 7671.
- Daisy-chaining between extraneous conductive parts. Not regulated by BS 7671.

'Discussing' these misunderstandings for me is a lot better use of my time than deciding whether I chisel up to the lighting circuit, or down to the socket circuit, when I want to add a shaver socket.

It's a no-brainer for me, and I'm not trying to escape proving my engineering judgement, just saving myself from the inevitable protracted discussion (I have the e-mail chains, unfortunately) for the sake of maybe 1/2 hour extra work and an extra heaped trowel of plaster.

 

[ericmark]

In the old days of PIR I have been asked to upgrade a hotel to comply and as I read the PIR I just looked at the client and had to say this guy was generating work for himself.

The problem is it is far harder to show it does comply when some one says it does not than other way around as one is looking for a fault and one first thinks I have missed something.

I would agree that the regulation number should be quoted and when I first moved from auto electrics to low voltage I was lead up the garden path many times where some one I respected told me that's not allowed.

The real problem is restrictions have been dropped we have seen this with bathroom earthing and there are many more like for example distance from sink to socket.

The problem is of course there is not just the BS7671 to consider and for example unless permission is granted there is a limit of 150W for an outside light this is building regulations not electrical regulations and one has to ask if one should or should not highlight this with a EICR?

Unlike the electrical regulations the Part building regulations are given in layman document with no reference number and so it becomes hard to insist on numbers.

I would not expect any house to get a clean bill of health and I personally think one is asking too much to expect one.