Spur from a spur

[Steve D]

Greetings all, and a Happy new Year !

Regarding (unfused) spurs, can anyone offer some guidance please.

I used to think that it was a cardinal sin to spur from a spur (unless you use a fcu) and I'm sure the regs (haven't got my regs to hand so can't quote the reg) says somewhere that an unfused spur can supply only a single or a twin socket.

However, the diagram they have of a typical radial final circuit in the appendices (Appdx 15 ?) shows an unfused spur feeding an additional 2 sockets.

Is this just an error in the diagram ?

Also, can you clarify exactly what is meant when they say "an unfused spur may be connected to the origin of the circuit in the consumer unit."

They're talking about the origin in the consumer unit, but surely they're not saying you can run a parrallel circuit (albeit only a single or twin socket) on the same breaker are they? That's the only way I can interpret that statement, but I thought that in other places in the regs they make it perfectly clear that each circuit needs it's own protection device.

Also, is there a difference in spurring from a socket and spurring from a junction box ?

Regards
Steve

 

[ian.settle1]

If you look at the diagram the cable is 4.0mm and not 2.5mm for a 32a CPD.

Here is a link to a update which came out in July IEE Wiring Regulations updates - The IET

 

[Steve D]

I see what you're saying regarding the radial diagram on the right hand side "An unfused spur run in 2.5 mm2 cable should feed one single or one twin socket-outlet only."

However looking at the radial diagram on the left hand side it clearly shows 'all live conductors' as 2.5mm2 and it shows spurring from a spur?

 

[ian.settle1]

I see what you're saying regarding the radial diagram on the right hand side "An unfused spur run in 2.5 mm2 cable should feed one single or one twin socket-outlet only."

However looking at the radial diagram on the left hand side it clearly shows 'all live conductors' as 2.5mm2 and it shows spurring from a spur?

Yes but look at what the protective device for the circuit that one is 20A for 2.5mm spur off spur and the other is a 32A device for 4.0mm off 4.0mm, it all comes down to the current carrying capacity of the cable.

 

[randyrat]

As far as spurring from the origin of the circuit in the CU goes, I take that to mean that you can run a spur from the SAME CU TERMINALS as the circuit you intend to spur from, rather than spur out of an existing socket on the circuit. Its a way of adding a spur without breaking into an existing circuit, but it still counts as a spur on that circuit.
Useful to know......

 

[Guest123]

Hey there.

When I was doing my training my old lecturer used to say to me there's 3 places you can spur from on a ring.

1. from an existing socket
2. from a joint box
3. from the mains board itself i.e off the same breaker.

If i spur off to a new twin socket I always use 4mm but, if only a single then 2.5mm.