Spur from a spur? Theoretical reason for it being allowed...

[DNS1]

Hi chaps...

Been asked to add a light in an under-stairs cupboard.

A spur from the downstairs socket circuit runs through that cupboard to a double 13A outlet in the kitchen. I'd like to tap into that for the light, but under the regs I'd have to fuse it down first.

The thing is, the 2.5mm T+E used is rated for 27A (in this case, method C). Worse case scenario is that both those sockets are used at 13A, so that's 26A being drawn.

The light which is going to be fitted is a very low energy LED fitting, so uses next to nothing. If the light is on and the sockets are used, the maximum that could be drawn through the spur is only ever so slightly over 26A, so the cable is still not overloaded.

Would anyone NOT fuse the spur in this instance (as it's clearly not a risk), or should it be done anyway as per the regs (and have the inconvenience of the blown 13A fuse if the toaster and kettle are used together)

 

[somersetsparks]

Spark 68 beat me to it lol

 

[somersetsparks]

That was it SS, I cannot think properly this time of night lol

On that note, think its time for bed!

 

[martinxxxxxx]

^^^^^What He Said^^^^^^^^
If some one adds something else later, perhaps a diyer and the place burns down, yoiu'd be in a very exposed situation with the minor works certificate. Always do it right - if we don't mhow can we get up and go tut tutting at all the diy work out there. Let the regs be your guide on everything.
If they want to cut corners - let them cut corner - we aint doing it for them

 

[lardy]

Surely it must have a FCU.
I appreciate the additional load will be negligible, the lighting spur, (1.5 = 20 A/ 1.0 = 15.5A) would easily take the load of the LED light, but what about fault conditions?
If it is on a 32A MCB, it would need additional protection.

 

[Adam]

So is wiring a 2.5mm radial to 1 Socket protected by a 32A MCB O.K. as well :cool3:

As a radial, no. However, you can connect it to the mcb of a ring final circuit as a spur.

 

[brman]

Surely it must have a FCU.
I appreciate the additional load will be negligible, the lighting spur, (1.5 = 20 A/ 1.0 = 15.5A) would easily take the load of the LED light, but what about fault conditions?
If it is on a 32A MCB, it would need additional protection.

It definitely needs an FCU, the question is where.
1) ring->spur->socket->fcu3A->light cct
2) ring->fcu13A->spur->socket->fcu3A->light cct
3) ring->spur->fcu13A->socket->fcu3A->light cct

The point being I believe you need a 3A FCU to protect the light cct anyway(10A rated accessories, regardless of cable capacity) , the question is whether you need the 13A fcu to protect the spur 2.5mm2 cable.

So I still argue that 1) is a pragmatic approach. Sure, if you managed to get a load greater than 1A but less than 3A on the light circuit it would "overload" the spur cable by up to 2A. Always assuming the sockets both have 3kW appliances connected, turned on and taking continuous current. But anything over 3A on the lights (i.e. a true fault condition) will be protected by the 3A fuse.

I would argue there is a damn site more than 2A leeway in the current capacity tables so the chances of
a) both sockets being continuously loaded to the max,
b) a fault on the lights taking greater than 1A and less than 3A and
c) the 2.5mm2 cable not being able to take 28A without melting
are so remote that I would not worry about it.

Like I said in the previous post, if it was practical i would do it "properly", but I wouldn't worry if practical reasons meant just fusing down the lighting cct bit.

Lets face it, we are all more than happy to let a 32A fuse protect an unfused spur cable, 27A rated, on the assumption that any fault will be protected by a downstream fuse in the plug. What happens if the fault is in the socket? And how many of us would worry if that unfused spur cable runs through a bit of insulation or gets grouped with other cables?

 

[GLENNSPARK]

I just can't understand why a FCU is being tried to be left out. Surely as per the regs (although I'm qualified spark - I am still learning and happy to receive advice) a FCU is required??!
But on a side note surely you would want to switch the light off?? The method you plan to use would mean your light would be on 24/7!!
I would much prefer to fit a FCU as you'd get protection, discrimination and also a means to switch on and off.

BS7671....atatutary or non statutary please...come on, quick as you like...