Understanding fused spur

[markus2025]

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I believe you currently have thisView attachment 397264


View attachment 397265View attachment 397266View attachment 397273

Essentially the simple rule is an unfused spur from a ring, be it from a socket or junction box etc may only be connected to one of these accessories: single socket or double socket or fused connexion unit. After the fuse in those accessories almost anything may be added.

Th

I believe you currently have thisView attachment 397264


View attachment 397265View attachment 397266View attachment 397273

Essentially the simple rule is an unfused spur from a ring, be it from a socket or junction box etc may only be connected to one of these accessories: single socket or double socket or fused connexion unit. After the fuse in those accessories almost anything may be added.

Thanks alot for the advise yeah so basically once you have a fcu on you can basically connect anything to the load side of the fcu obv aslong as you have the correct fuse in the fcu

So on a other questionnwith regards to coming from a juction box in the loft to bring a new 13amp fcu whats the rules on this can you only bring 1 supply from one junction box and if you wanted another you would have to cut into the ring and add another junction box ?

But yeah covering my orginal question i though if you had a single run of 2.5mm coming from a junction box in a loft down to single/double socket you could then spur off that socket with a fcu and the add as many as you want but the ruling is you need to removed the double/single socket and replace it for a fcu then add your sockets aftwards which you have confirmed

but if the socket was on a ring showing by having 2L 2N 2E then it would be ok in that instance to then add a fcu so the socket would then have 3 cores going into and in and a out for the ring and then a cable off to the fcu

Again thanks alot for the help

 

[SUNRAY]

⁴


Th

Thanks alot for the advise yeah so basically once you have a fcu on you can basically connect anything to the load side of the fcu obv aslong as you have the correct fuse in the fcu

So on a other questionnwith regards to coming from a juction box in the loft to bring a new 13amp fcu whats the rules on this can you only bring 1 supply from one junction box and if you wanted another you would have to cut into the ring and add another junction box ?

But yeah covering my orginal question i though if you had a single run of 2.5mm coming from a junction box in a loft down to single/double socket you could then spur off that socket with a fcu

No

and the add as many as you want but the ruling is you need to removed the double/single socket and replace it for a fcu then add your sockets aftwards which you have confirmed

Correct

but if the socket was on a ring showing by having 2L 2N 2E

As long as someone has not been naughty and added a second socket to a spur

then it would be ok in that instance to then add a fcu so the socket would then have 3 cores going into and in and a out for the ring and then a cable off to the fcu

Correct

Again thanks alot for the help

 

[SUNRAY]

If your ring final runs in the loft and drops down to each socket, essenntially you can add additional points in the loft quite easily

 

[markus2025]

Once again thanks for the help
My loft circuit is quite old and quite a few points around the house have been ran off 30a junction boxes on a single run of cable and i belive if this is the case you then should not be running a fcu off the back of that double socket

How many single runs can you do from one 30a junction box

Many thanks

 

[ebee]

If a Ring Final Circuit is in T & E 2.5 for example (or 1.5 if "Pyro" usually) then you may spur anywhere either from the ring itself using say a junction box or for any point(socket, twin or single) and/or at the origin of the circuit (i.e. at the fuseway) .
That is pretty much the accepted way of running a Ring Final Circuit.
If you decide to have no more on spurs than on the ring proper itself it is a rule to encourage good housekeeping and is usually applauded.
If you try to keep a ring roughly balance by spacing according to load requirements fairly equally distributed around the ring with load itself and likely perceived duration of such or, alternatively, within the middle one third of the ring length total is usually a good idea in basis, if only for the fact it does not "cook" and "age" cables in some places faster than others for one thing - no need for massive reams of calculation but a quick "back of a fag packet" idea is usually acceptable.
In a similar way you would try to avoid running as if a radial except at the last point you make a longish run back to the origin, that is not a good idea for getting benefits of a ring final usually anyway.
You could actually run any number of radial spurs (not just one) to a single point (twin or single socket) but that is often baulked at purely for good housekeeping in effect. In fact if you did all that then removed the ring itself some might consider it has become suddenly "dangerous" by doing so, and in itself for no good reason to think so really.
In some instances a defect on a Ring Final Circuit might be safer than a similar defect on a Radial Final Circuit and yet again vice versa.
You might decide whether to run a ring v a radial for a host of reasons.
The UK (and some that follow) are quite unusual because of the Ring Final Circuit idea, that in itself does make us any better or any worse solely because of that although it could sometimes be considered worse under certain likelihoods of some defects becoming present.

In my book, no clear winner overall, horses courses!

PS - Because of my age was brought up by the "Rings are Kings" era so am I liable to be biased? Some might think so yet I do not, if I were 60 years younger or 60 years older then I have no idea how I would view those differences.

 

[securespark]

I haven't

Nor me.

In 30 years.

 

[pete01]

Nor me.

In 30 years.

I thinks it very hard to overload a 2.5mm on a 32 amp mcb, although it says 27 amps ish, it can definitely take a lot more for a long time......probably

 

[JohnW2]

I thinks it very hard to overload a 2.5mm on a 32 amp mcb, although it says 27 amps ish, it can definitely take a lot more for a long time......probably

Quite so. We at least know that it is deemed to be able to carry 39.15 A (27A x 1.45) for an hour without coming to any harm.

 

[EFLImpudence]

If a Ring Final Circuit is in T & E 2.5 for example (or 1.5 if "Pyro" usually) then you may spur anywhere either from the ring itself using say a junction box or for any point(socket, twin or single) and/or at the origin of the circuit (i.e. at the fuseway) .
That is pretty much the accepted way of running a Ring Final Circuit.
If you decide to have no more on spurs than on the ring proper itself it is a rule to encourage good housekeeping and is usually applauded.
If you try to keep a ring roughly balance by spacing according to load requirements fairly equally distributed around the ring with load itself and likely perceived duration of such or, alternatively, within the middle one third of the ring length total is usually a good idea in basis, if only for the fact it does not "cook" and "age" cables in some places faster than others for one thing - no need for massive reams of calculation but a quick "back of a fag packet" idea is usually acceptable.
In a similar way you would try to avoid running as if a radial except at the last point you make a longish run back to the origin, that is not a good idea for getting benefits of a ring final usually anyway.
You could actually run any number of radial spurs (not just one) to a single point (twin or single socket) but that is often baulked at purely for good housekeeping in effect. In fact if you did all that then removed the ring itself some might consider it has become suddenly "dangerous" by doing so, and in itself for no good reason to think so really.
In some instances a defect on a Ring Final Circuit might be safer than a similar defect on a Radial Final Circuit and yet again vice versa.
You might decide whether to run a ring v a radial for a host of reasons.
The UK (and some that follow) are quite unusual because of the Ring Final Circuit idea, that in itself does make us any better or any worse solely because of that although it could sometimes be considered worse under certain likelihoods of some defects becoming present.

In my book, no clear winner overall, horses courses!

PS - Because of my age was brought up by the "Rings are Kings" era so am I liable to be biased? Some might think so yet I do not, if I were 60 years younger or 60 years older then I have no idea how I would view those differences.

What?

If you decide to have no more on spurs than on the ring proper itself it is a rule to encourage good housekeeping and is usually applauded.

Extra - what nonsense.

Have you been to any bungalows?

 

[securespark]

I thinks it very hard to overload a 2.5mm on a 32 amp mcb, although it says 27 amps ish, it can definitely take a lot more for a long time......probably

I went to a job where the customer complained the shower had packed up. Of all the jobs I visited, electric showers not working were pretty much top of the list.

This one was a 9.5 fed with 2.5 cable. It turned out it used to be a 7.5 shower then it was upgraded by a DIYer. It lasted a fair while before shriveling up to be fair.

 

[ebee]

What?


Extra - what nonsense.

Have you been to any bungalows?

Indeed I have been to bungalows, the info I put about rings have been in vogue at one time or another as being so called official guidance by the great and good or so for quite a few years each.
Exactly why it was taught than no more spurs than on the ring proper became a well adopted rule I have no idea and as such as far as I am concerned if you had 12 points on the ring and each one fed a spur and between each point on the ring you had another 13 points and then from the fuseway you had two points you would certainly have a lot more on the end of spurs than on the ring itself but what would it matter.
Similarly you might have zero points on the ring proper and 100 points spurred from the ring and what would that matter either?

The only reason I could envisage is to reduce hap hazard thinking/good housekeeping or good planning as against adding things piecemeal.
But why were such things taught? I do not know!

Some of the rules are made and adhered to are done so as a good practice (sometimes) even though the regs might not actually state them.

 

[EFLImpudence]

Yes, I just thought when reading about the shower upgrade on too small a cable.

IF the reason for only one single socket on a (2.5mm²) spur is to prevent two singles being increased to two doubles, why then do they not just insist on 4mm² for all spur cables and with reference to the shower, why not insist on 10mm² - or 16mm² - cable for showers?

 

[JohnW2]

This one was a 9.5 fed with 2.5 cable. It turned out it used to be a 7.5 shower then it was upgraded by a DIYer. It lasted a fair while before shriveling up to be fair.

Are you talking about the cable 'shrivelling up'? If so, I'm more than a little surprised ...

... even if the 9.5 kW is quoted for 230V (unlikely) that only represents 41.3 A and, as I recently wrote, Method C 2.5mm² cable is deemed to be able to carry 39.15 A for an hour without coming to any harm - and, even in the presence of teenage daughters, showers rarely last for an hour

 

[JohnW2]

IF the reason for only one single socket on a (2.5mm²) spur is to prevent two singles being increased to two doubles, why then do they not just insist on 4mm² for all spur cables ...

You talk about 'insisting' but, as you are aware, the suggestion that an unfused 2.5mm² spur should not supply two single sockets is only 'informative guidance'.

 

[EFLImpudence]

You talk about 'insisting' but, as you are aware, the suggestion that an unfused 2.5mm² spur should not supply two single sockets is only 'informative guidance'.

I didn't say they did insist on anything; I said why do they not insist on 4mm² for the spur?