table lamp circuit off a fused spur

[danielsan]

Hi,
while I have the living room floor up and have added in some extra sockets on my ring main (which only serves that room) I would like to install a table lamp circuit - we use table lamps for low level lighting and I would like to be able to switch them all on and off at a single switch.
So ive got some (2A rated) small round pin sockets and plugs (5 of each) and have run a circuit of 1.0mm2 cable between them
To avoid having to take this back to the RCD as a new circuit, can I feed this table lamp circuit off a fused spur off the ring main? I would put a 2A fuse in the switched fuse unit. Of course the spur to the fuse unit would be 2.5mm2
1) is this acceptable under the regs
2) is it ok to wire both ends of the table lamp circuit into the 'load' terminals in the switched fuse unit - so the power can flow either way ie acting a circuit, but fed by a spur?

I have added up the current likely to be drawn form the lamps I intend to plug in, at 0.3 amps I figure the 2A fuse and rating on the plus/sockets should be ok.

any advice/corrections would be much appreciated - new to the forum: so sorry this is long. I have a reasonable amount of experience of adding in new sockets, extending lighting circuits (understanding the loading issues), but never go anywhere near the RCD unit - if I cant add something in to an existing circuit then its off bounds as far as im concerned.

 

[holmslaw]

..

 

[TicklyT]

80 Watts of incandescent lighting may be a bit dim, but 80 Watts of CFLs or LEDs could be a bit .

That might throw the current calculation out though, as the power factor could be at right angles to reality.

 

[danielsan]

Wow, those a quick responses and thanks.
re the load - I have 70w made up from two lamps wiht the tiny halogen bulbs ( a 40 and a 20) and another lamp with two 5w CFLs. would probably add another larger floor lamp with a CFL of up to 20w

so my calculation was watts = volts x amps solved for Amps, which gave me 0.3. does this apply when considering CFLs with lower wattage for given light output - would appreciate more info on that

 

[danielsan]

oh, forgot to say - given your estimation of 80w lighting, that I had used 220 v as i figured that would overestimate my amperage

Tickly T - without burdening you could I ask what is meant by the power factor being at right angles to reality?

 

[ban-all-sheds]

we use table lamps for low level lighting and I would like to be able to switch them all on and off at a single switch.

Do you plan to use the switched FCU for this purpose, or do you want to use a light switch gang?

To avoid having to take this back to the RCD as a new circuit, can I feed this table lamp circuit off a fused spur off the ring main?

Yes.

I know you keep saying "RCD", but you're using it in a sense which means "consumer unit" - is your socket circuit RCD protected?

I would put a 2A fuse in the switched fuse unit.

Better buy a supply of those - they aren't widely available. But 3A would also be OK.

Of course the spur to the fuse unit would be 2.5mm2

Can you not put the FCU directly onto the socket circuit, rather than making it a spur?

1) is this acceptable under the regs

• http://www.voltimum.co.uk/files/gb/attachments/niu/l/attachments/c5-43.pdf
• http://web.archive.org/web/20061110111450/http://www.niceic.org.uk/downloads/concealedcables.pdf
• IEE article
• IEE Article on 17th Edition requirements for concealed cables.

2) is it ok to wire both ends of the table lamp circuit into the 'load' terminals in the switched fuse unit - so the power can flow either way ie acting a circuit, but fed by a spur?

Why would you want to?

Tickly T - without burdening you could I ask what is meant by the power factor being at right angles to reality?

http://en.wikipedia.org/wiki/Power_factor

 

[danielsan]

thanks ban-all-sheds
to try and fill out the details in order
1) was going to just use the switched spur unit for switching the circuit, in large part I guess as I had been thinking of a (ring) circuit from the fuse unit and couldnt work out how to switch it downstream from the fuse unit
2) yes, thanks for the correction, i guess i mean consumer unit: my ignorance on the difference probably constitutes a can of worms
3) hadnt thought/realised I could put the fuse unit in the ring main, not on a spur. presumably I would just be wiring in/out 2.5 mm2 wires on teh ring main circuit into the 'supply side' terminals of the fuse unit?
4) wrt wiring a ring of 1.0 mm2 for the table lamp circuit, I guess I wasnt sure about having a daisy-chain of small sockets, but I guess your saying its not necessary as the whole 'circuit' is fused to 2A at the fuse unit

thanks again

what one monkey can do, so can another
but some monkeys are better trained than others!

 

[ban-all-sheds]

was going to just use the switched spur unit for switching the circuit, in large part I guess as I had been thinking of a (ring) circuit from the fuse unit and couldnt work out how to switch it downstream from the fuse unit

There you go - no need for the lighting sockets to be on a ring, so a switch(es) on the wall get easier. You could even have dimmer switch(es) if you want, but you'd need to take care which CFLs you used.

presumably I would just be wiring in/out 2.5 mm2 wires on teh ring main circuit into the 'supply side' terminals of the fuse unit?

Yup.

wrt wiring a ring of 1.0 mm2 for the table lamp circuit, I guess I wasnt sure about having a daisy-chain of small sockets, but I guess your saying its not necessary as the whole 'circuit' is fused to 2A at the fuse unit

But so would it be if you had them in a ring.

 

[Paul_C]

I'd go up from 2A at the FCU if you are planning on installing five 2A sockets. You might only be thinking of using low-power CFL's at the moment, but there might come a time you decide to plug in two or three incandescent lamps of higher rating.

In the older editions of the Regs. when BS546 outlets were still common place, the allowance was for "at least 0.5 amp" for each 2A socket on a circuit.

 

[danielsan]

Thanks paul C - for clarification, are you suggesting to keep the round-pin sockets and plugs, rated at 2A, but increase the fuse rating in the fuse unit (say to 3A) Ban-all-sheds also suggested 3A fuse would do - but would this not mean that the rating of the plugs and sockets was not protected adequately by the fuse?

 

[Taylortwocities]

The 3a fuse in the FCU is to protect the 1.0mm² cable that will run from socket to socket.

The sockets themselves are rated at 2amp. This means that the sockets and plugs at each light point can handle 2amps through them (to their attached lamps)

2 amps = nearly 500watts of light (2amps x 230volts). So it is OK to do this.

 

[Paul_C]

The sockets are rated for 2 amps, but at these low current levels it's permissible to protect them with a fuse of higher rating. The reasoning is that the normal load is limited by the appliance (a small table lamp in this case) which is connected to the socket, and a short-circuit will cause sufficient current to flow immediately to blow the fuse.

In the days when 2A lighting sockets were widely used, it was common for them to be wired to a regular 5A lighting circuit.

 

[securespark]

What do you mean, "in the days"????

That day is not done yet!!

 

[Paul_C]

I meant in the days when they were much more commonplace than they are today.