FCU spur on spur acceptable?

[Delboybully]

I sometimes get some work helping a fellow sparky. Last week he asked me to help him on wiring a loft conversion. He is the one responsible for the cert (design, install and testing). I was just the hired help.

He said we are going to take a spur from the ring to a 13A FCU for the sockets and a 3A FCU for the lights (personally i would of extended the ring- the Zs was low enough to do this). I suggested taking a feed from the lighting circuit for the lights but he told me the customer didnt want the boards taken up or the additional costs this would of occured. So as i was wiring up the FCU's i took a feed from the load of the 13A FCU to feed the 3A FCU for the lights. He said he didnt want it done this way because if the 13A fuse goes then the lights will be lost. He wanted the feed for the 3A FCU for the lights to be taken from the supply side of the 13A FCU. I said this isnt allowed as its a spur of a spur. He said that the spur cable cant be overloaded so its ok.

Now i can see his argument and it makes sense but i still say it not allowed in the regs as its a spur of a spur. What do you all think.

 

[Farmelectrics]

Strange you have a feed up there anyway for the upstairs lighting circuit why not just extend this to the loft conversion

 

[Hiddo]

It's a spur off a spur, so no can do!!

Without seeing the job it's difficult to advise what to do, but another way to do it would be to break the ring twice and provide two spurs.

If you can get at the ring then surely you can get at the lighting circuit?

 

[timo1]

Sounds less than ideal but I'm guessing there must be a good reason he's opted to do it this way. I'm struggling to picture it but it is a spur off a spur isnt it? Although the cable would never get overloaded as the 3a fuse would protect it. I would have thought that 13a would be enough for sockets and lamps in a loft, the most loading they would see would be a hairdryer and some table lamps or a t.v surely?

 

[telectrix]

it's not a spur off a spur, it's 2 spurs taken from the same point on the RFC. each one is fused accordingly.

 

[Delboybully]

It is a spur of a spur.

A spur to the loft was taken from a socket on the ring on the upstairs ring circuit to a 13A FCU. From the feed side of the FCU (unfused) then fed the 3A FCU. The 13A FCU fed the loft sockets and the 3A FCU did the lights. The reason the lights were not fed from the upstairs lighting circuit was because the customer didnt was the additional costs associated with taking up all the tongue and groove boards that had been laid. Please remember i was only helping with this, i wasnt involved with the costings or the design etc. I didnt like the idea of the sockets and lights being on the same circuit (and thus the same RCD).

Personally given the customer restraints i would of extended the ring at least to the 13a FCU then spurred from that to the 3A FCU thus no spur of a spur. It isnt that much more work to run two cables through the same route as it is one. There Zs was easily low enough and there was enough room in the ring socket back box to extend the ring.

In my book it is a spur of a spur which isnt allowed in the regs, however i can also see the other sparks argument in that the spur cant be overloaded so is safe. What do you all think, acceptable or not

 

[Moses]

It is a spur of a spur.

A spur to the loft was taken from a socket on the ring on the upstairs ring circuit to a 13A FCU. From the feed side of the FCU (unfused) then fed the 3A FCU. The 13A FCU fed the loft sockets and the 3A FCU did the lights. The reason the lights were not fed from the upstairs lighting circuit was because the customer didnt was the additional costs associated with taking up all the tongue and groove boards that had been laid. Please remember i was only helping with this, i wasnt involved with the costings or the design etc. I didnt like the idea of the sockets and lights being on the same circuit (and thus the same RCD).

Personally given the customer restraints i would of extended the ring at least to the 13a FCU then spurred from that to the 3A FCU thus no spur of a spur. It isnt that much more work to run two cables through the same route as it is one. There Zs was easily low enough and there was enough room in the ring socket back box to extend the ring.

In my book it is a spur of a spur which isnt allowed in the regs, however i can also see the other sparks argument in that the spur cant be overloaded so is safe. What do you all think, acceptable or not

What happens when the 3A fuse blows and the customer only has a 13A fuse to replace it and then what?

 

[Silly Sausage]

What happens when the 3A fuse blows and the customer only has a 13A fuse to replace it and then what?

That would apply to the countless 1000s of fused spurs across the country.
You can only design and install a compliant installation, you can't be responsible for what happens it in the future.

 

[Jimmy Boy]

A protective device fuse/cb etc is there to protect the supply cable not the end usage although in many cases it does so if someone put a 13A in a FCU feeding lights in theory it would be difficult to overload it ( That doesn't make it right of course ) so you need to consider whether enough fault current would flow under fault conditions in a 1mm cpc to operate the device or blow the 13A fuse within the prescribed time in the regs, lets work it out someone.

 

[AndyL]

You are right dellboy, it is two points fed from an unfused spur which is not allowed.
The lights should be fed from the fused/load side of the 1st FCU

 

[flake]

Its strange to know. Really like it..

 

[B16 Tom]

Thats a not in my book :cry_smile: Sometimes its better not to do the work than have a customer dictate how things are done.
Do you tell a mechanic how to fix ya car?? Why tell a spark how to do his job??? Many customers do it and advise them to try some1 else, they usually come back:tongue3:

 

[jamie-spark]

Its not how i would do it and spurs off spurs maybe a no no. With that said what he has done and the way he has done it it is no worse than a spur off the ring with a twin skt . where the potential current flow in that cable could be 26 amp say ( which is unlikley and if it were would not be for long, unless he is growing something in the loft lol) Or say one twin skt with a 13 amp mutiplug extension and a table lamp plugged in . due to the nature and protection its unlikely the spur cable is going to be overloaded

IMO
again not how i would go

 

[Adam W]

I reckon best to extend the lighting circuit. This guy you're working with mentions having no lights if the 13A fuse goes, well you wouldn't have any lights if the MCB tripped either, but you would if the lights and sockets were on different circuits, which is one of the reasons we do it.

 

[dwardy]

if the customer knows so much about what needs doing he should do it himself. cutting corners to make things easier/cheaper is the quickest way to cause injury/fire. tell your friend to remember whose name is going on that cert. if he is only putting a 3A fuse there he has no worries about it blowing the 13A fuse and should connect it off the load side, where he can have as many extra sockets as he wants (providing volt drop requirements are met)