Spur question

[sneakers]

In my understairs cupboard there is spur which powers an alarm panel via a fused connection box, the spur cable is routed through a hole in the wall to the back of a double socket in the sitting room.

I want to add a single socket in the same understairs cupboard, can I (or more likely an electrician) wire it in on the same spur, before the alarm panel's fused box?

 

[AndyPRK]

I don't think an electrican could as it would be breaking the regulations.

In practice there would be no hazzard though

 

[PrenticeBoyofDerry]

In my understairs cupboard there is spur which powers an alarm panel via a fused connection box, the spur cable is routed through a hole in the wall to the back of a double socket in the sitting room.
I want to add a single socket in the same understairs cupboard, can I (or more likely an electrician) wire it in on the same spur, before the alarm panel's fused box?

There certain regulations/requirements to uphold when taking a spur from a socket circuit, the nature of the spur that can be taken would depend on what type of socket circuit the spur has been taken from. There two main types of socket circuit, one is a ring fing final, where the regs are a little more stricter for spurring and the second is a radial circuit.

So to give you an informed answer we would need to know a little more about the feed socket/circuit.

In general you can only take one unfused socket outlet from a ring final socket, so cannot spur from a spur, but if a 13 FCU was connected at the point of intersection at the feed socket then you could have a number of socket outlets and the addition of the FCU for the alarm. But would be restricted to a maximum load of 13A.

The radial circuit is a little more flexible and there are no requirements to protect multiply sockets via a FCU.

 

[AndyPRK]

If it were a ring the fuse would be 30/32A

Radials are usually fused at 15/16/20A


In the fusebox / consumer unit.

 

[sneakers]

I don't know if it's radial or ring i'm afraid, I think i'll need a professional to look at this.

I'm not sure what rating the FCU is but would have thought it was less that 13 for an alarm panel, it's a box with a pull out fuse on a tray type

In my mind I had imagined fitting the new socket between the feed socket and the existing FCU. Are you saying that the new socket should be wired at (after) the FCU?

 

[JohnW2]

In my mind I had imagined fitting the new socket between the feed socket and the existing FCU. Are you saying that the new socket should be wired at (after) the FCU?

To be compliant with regulations, it would have to be wired from the load side of the FCU (together with whatever the FCU is currently supplying). However, your alarm might call for a fairly small fuse (maybe 3A) in that FCU, which, if so, would obviously seriously limit the amount of current available to your new socket. If that issue arose, the 'proper' solution would be to insert a second FCU (with a 13A fuse) in the feed to the present FCU and to wire your new socket off the load side of that new FCU - that would limit your new socket to around 13A, but that would be better than 3A!

Another approach which many might regard as 'bad practice' but which, as far as I am aware, does not actually contravene any regulations (except possibly the instructions of the manufacturer of the socket about how many wires could go into each terminal - you would then have 4 conductors per terminal) would be to wire your new socket as a second spur from the same double socket in your sitting room.

Kind Regards, John

 

[JohnW2]

If it were a ring the fuse would be 30/32A. Radials are usually fused at 15/16/20A

You're thinking only 2.5mm² cable. "A2 circuits" (30/32A 4mm² ones) are not at all uncommon.

Kind Regards, John

 

[Risteard]

does not actually contravene any regulations (except possibly the instructions of the manufacturer of the socket about how many wires could go into each terminal - you would then have 4 conductors per terminal) would be to wire your new socket as a second spur from the same double socket in your sitting room.

Not permitted, as it could pull an excessive current through one leg of the ring.

 

[bernardgreen]

would be to wire your new socket as a second spur from the same double socket in your sitting room.

Not permitted, as it could pull an excessive current through one leg of the ring.

Which highlights how poorly constructed the regulations are

Suppose you replace the double socket with two singles in a dual box and then take a spur from each single socket. Will the 3 inches of ring cable between the two single sockets have any effect on how much current is flowing in each leg of the ring ?

 

[JohnW2]

does not actually contravene any regulations (except possibly the instructions of the manufacturer of the socket about how many wires could go into each terminal - you would then have 4 conductors per terminal) would be to wire your new socket as a second spur from the same double socket in your sitting room.

Not permitted, as it could pull an excessive current through one leg of the ring.

Someone always says that! For a start, there's only any sense at all in the suggestion if the spur joins the ring very close to one of its ends. Secondly, few people would complain if there were two sockets on a ring, with six inches of cable between them, each supplying a spur - and few would even think to question two or more double sockets fairly close to one end of a ring. There is no regulation which explicitly prohibits two spurs having the same point of origin, so if a sensible electrician does not believe that there is a significant risk of overloading one leg of the ring, then I see no problem.

In terms of 'sensible', you presumably would have no problem with the double socket being spurred from the socket in question. Do you then seriously believe that also having a feed to an alarm hard-wired via a (probably) 3A FCU spurred from the same point on the ring would create a risk of 'pulling excessive current through one leg of the ring'?!!

Kind Regards, John

 

[JohnW2]

Not permitted, as it could pull an excessive current through one leg of the ring.

Which highlights how poorly constructed the regulations are ... suppose you replace the double socket with two singles in a dual box and then take a spur from each single socket. Will the 3 inches of ring cable between the two single sockets have any effect on how much current is flowing in each leg of the ring ?

No, it's not a poorly-constructed real regulation, it's one that Risteard has invented. All the regs require is that the designer is satisfied that the design is such that "the load current is unlikely to exceed the CCC of the cable for long periods of time". Any sensible electrician would hopefully believe that what I was suggesting (in the context of this thread) did not make such an event 'likely'!

Kind Regards, John

 

[PrenticeBoyofDerry]

I don't know if it's radial or ring i'm afraid, I think i'll need a professional to look at this.

It would be difficult to tell by the untrained eye, even the trained eye can have problems, there is no real way of telling without testing the circuit out, regardless of the fuses that are connected to the circuit, normally a ring final would be protected by a 30A/32A fuse/breaker but so can a radial circuit, I have also come across occasion where the ring final has been split across two protective device which can also leave someone somewhat puzzled, so only really investigation and testing would prove.

I'm not sure what rating the FCU is but would have thought it was less that 13 for an alarm panel, it's a box with a pull out fuse on a tray type

The alarm system will very likely be on a 3A fuse but in truth will not use 1A of current.

In my mind I had imagined fitting the new socket between the feed socket and the existing FCU. Are you saying that the new socket should be wired at (after) the FCU?

You should install the 13A FCU directly after the feed socket, then you new socket and then the FCU for the alarm.
There is one other issue that all new socket outlets require 30mA RCD protection, if this does not already exist on the circuit, the a combined RCD/FCU would be recommended. If not already mentioned not read all the replies since mine early on.