fused spur wiring... advice

[Jake1579]

i was at work today replacing some sockets and backboxes and there was 2 fused spurs im a 1st year apprentice... i dropped the faceplates put the new backboxes in etc... and there was a linking cable for the 2 fused spurs and i linked the supply and the actual linking cable together in the supply terminals. But on the other one there was no load connected to it, it was just the linking cable and this is the bit im worried about i put the l and n in the supply side and i dont think that was right... at the time i thought it was right so i didnt ask any questions

 

[baldsparkies]

Never be afraid, or too proud to check with someone with more experience.
Your on a long learning curve and need to get the work you have done verified by someone who is physically with you, on site.
Forums are good, but advice is limited to your explanation and as such open to interpretation.
Like I said, if in doubt ask someone your senior to check, they will think more of you for it.

 

[Andy78]

Never be afraid, or too proud to check with someone with more experience.
Your on a long learning curve and need to get the work you have done verified by someone who is physically with you, on site.
Forums are good, but advice is limited to your explanation and as such open to interpretation.
Like I said, if in doubt ask someone your senior to check, they will think more of you for it.

Sound advice. An apprenticeship is there for you to learn your craft. Ask the guy(s) supervising you.

Also there is a trainee forum here to join, with mentors to give you lots of guidance on your journey.
Announcements - Trainees Only

 

[Richard Burns]

Do ask the question of those who are meant to be advising you on the correct methods.
If you have wired it like the below diagram then it should not be a problem but does not strictly meet the recommendations in the regulations as you should only feed one double socket or one fused connection unit off a spur.
The diagram below shows two fused connection units off one spur.

 

[PiousJim]

Would this method fail in terms of regulations? The reason I ask I had a tutor once tell us "From the ring Main you can spur to a FCU then from there you could add as many sockets and FCU as you need/wanted" to be honest at the time it didn't feel right.

 

[Andy78]

Would this method fail in terms of regulations? The reason I ask I had a tutor once tell us "From the ring Main you can spur to a FCU then from there you could add as many sockets and FCU as you need/wanted" to be honest at the time it didn't feel right.

Have a think about current carrying capacities of the cable used, the potential load drawn in sections of a circuit and the current any part of the circuit may be subjected to, and protective devices for overcurrent used for the different sections of the circuit.
Reference your thinking with appendix 15, appendix 4, and chapter 43.

 

[PiousJim]

I did have a look at appendix 15, I still didn't feel confident that we could spur to a FCU then to a second FCU (on the same radial).

Going to have a look at appendix 4, and chapter 43.

Thanks Andy

 

[Richard Burns]

MY diagram above would be OK if the second SFCU were fed from the load side of the first FCU (rather than the supply side) because the maximum current that can be taken on the single spur cable is 13A.
However two FCUs as in the diagram can only take 26A which might unbalance the ring but would not overload the cable.

 

[Dave OCD]

Are you sure Richard ? I'd say 26 amps is really pushing it for 2.5, especially when the fuses will allow more than 13 amps to flow for a period of time in reality.

 

[Richard Burns]

It would of course depend on the method of installation of the cable but if it is clipped direct the tabulated current carrying capacity is 27A.
One of the requirements for protection against overload is that if the cable because of the nature of the load is not likely to overload you do not need to protect against overload.
A 13A fuse would be suitable to protect a cable with a 13A current carrying capacity against overload, even though the fuse could take more current for a period of time as this is accounted for in the design.
Similar considerations apply to the 27A current carrying capacity cable.

There is no pushing it consideration, there are limits which must not be exceeded, I am not saying it is good design, (I am actually saying it is bad design) however it would not be a risk of overloading the cable.

 

[M-Ty]

It would be interesting to know the load on the first.
However, the second is stated to have nothing connected.
Is it not reasonable to assume that the characteristics of that "load" are currently such that it draws no current and therefore cannot cause an overload, and it would be the responsibility of whoever intends to connect something to it to take into account the cable rating and existing load to ascertain its suitability?

 

[Dave OCD]

It would of course depend on the method of installation of the cable but if it is clipped direct the tabulated current carrying capacity is 27A.
One of the requirements for protection against overload is that if the cable because of the nature of the load is not likely to overload you do not need to protect against overload.
A 13A fuse would be suitable to protect a cable with a 13A current carrying capacity against overload, even though the fuse could take more current for a period of time as this is accounted for in the design.
Similar considerations apply to the 27A current carrying capacity cable.

There is no pushing it consideration, there are limits which must not be exceeded, I am not saying it is good design, (I am actually saying it is bad design) however it would not be a risk of overloading the cable.

Yes but that initial stated tabulated rating is without any de-rating factors whatsoever Richard and of course considerations on cable length and volt drop. A single 2.5mm spurred off a RFC feeding two 13 amp fused spurs could be overloaded fairly easily I think, but neither of us would do that anyway. :smile5: