Fused light switches. When do you use em?

[Dooby]

I've just come back from the parents and it's a very old house that's had a couple recentish rewires.
They had a few fused light switches, one was for a bathroom light, one was for an outside light. Now normally I'd think spurs, but there was always lighting there that I know. And the special locations thing, well they weren't on all bathroom and outside lights.
Is it as straightforward as fused light swtiches = spur?

Am dismayed have to ask this as google has let me down.

 

[trev]

Pics would help but they certainly sound like fused spurs mate. Is there a separate lighting circuit or are the lights powered from the RFCs?

 

[Dooby]

Ha, didn't occur to me to take pics, I was at the parents, I was too busy necking port and scoffing cakes. Ok RFC is not on the acronym list here and I've got in one of my dyslexic tangles having immediately thought of many things that could be.
I couldn't get to see the CU this time, thought there were several lighting circuits on it so didn't know it would jsut be a spur - but you've satisfied me they probably were. Am always worried am missing something obvious.

 

[Marvo]

Ok RFC is not on the acronym list here

RFC stands for a 'Ring Final Circuit'. It's a circuit that runs from the CU through the various sockets on the circuit then back to the CU again at the far end. An RFC would have 2 lives in the MCB 2 neutrals on the neutral bar and 2 earth wires on the earth bar.

A spur is where an extra circuit is run using a single cable from somewhere on the RFC.

 

[Dooby]

Ahh cheers for that, I know exactly what a ring final circuit is, couldn't think what a RFC was, if you know what I mean. Terrible with acronyms.

RFC stands for a 'Ring Final Circuit'. It's a circuit that runs from the CU through the various sockets on the circuit then back to the CU again at the far end. An RFC would have 2 lives in the MCB 2 neutrals on the neutral bar and 2 earth wires on the earth bar.

A spur is where an extra circuit is run using a single cable from somewhere on the RFC.

 

[Paul.M]

Just to add to the teaching, please remember a basic thing that most trainees forget and try to over engineer.

The fuse is there to protect the cable. (told you it was simple )

If the cable can not handle the amount of maximum amps from the protective device which it is being fed from, it needs to be "fused down". Look at the list below.


C/U = 100A main fuse to feed a buzz bar.

From 100A buzz bar to RFC = 32A to protect a 2.5mm RFC.

Spur from 32A RFC to a light circuit = 5A to protect 1.5mm cable (radial).


If you downsize the csa of the cable you must protect it by the use of a fuse.