spur query

[bones75cbr]

Why is it advised that you cannot take a spur of a socket that is already a spur?

 

[andy]

Why is it advised that you cannot take a spur of a socket that is already a spur?

because it will overload the cable.

 

[kai]

The way round it is to fit a 13amp fuse connection unit at the very beginning of the run, and then run the sockets from that.
This ensures the whole spur cable is protected along it's entire length.

 

[Lectrician]

Rings...hate them!

Radials is the way!

 

[felix]

A ring main is typically wired with 2.5mm cable rated at 20 amps. A socket on the ring has two parallel cables back to the consumer unit. Between them these can carry 40 amps although the current won't always divide equally. The upshot of this is that a ring of 20 amp cable can be protected by a 30 amp fuse.

Now look at a spur. It's only one piece of 20 amp cable but it's still on a 30 amp fuse. This is looking dodgy already but at least you can only put one 13 amp fused plug into it. (I'm sure it used to be two sockets allowed on a spur.) If you attach a spur to another spur you can draw rather more current than the cable can carry but not blow the 30 amp fuse.

It gets worse. How do you know that the spur you are about to attach to isn't already attached to a spur? If it is then you're pushing the possible load up to 39 amps.

 

[plugwash]

HOWEVER

the iee regs do not make any allowances for load duration in cable calculations. So in practice spurs off spurs and broken rings are rarely too much of a problem.

not that you should be doing it but kitchen fitters leave broken rings all the time and it doesn't seem to cause many problems.

 

[steve190]

HOWEVER

OSG states that an unfused spare may supply one single or one twin or one multiple socket outlet. So a triple takes us up to 39 Amps again.

 

[andy]

HOWEVER

OSG states that an unfused spare may supply one single or one twin or one multiple socket outlet. So a triple takes us up to 39 Amps again.

no. there rated at 13A max, even if double or triple.

 

[plugwash]

triple sockets are always fused so would presumablly be treated the same as a socket fed through a FCU though i don't belive the regs explicitly mention them.

 

[ban-all-sheds]

HOWEVER

OSG states that an unfused spare may supply one single or one twin or one multiple socket outlet. So a triple takes us up to 39 Amps again.

You'll be telling us next that a double socket means 26A....

 

[steve190]

So from this I take it that it is impossible to plug two 13 amp plugs into a twin socket.


And if each 13 amp plug had a 3 Kw radiant heater on the end it still only comes to 13 amps

Triple sockets are always fused? MK are but I don't believe to 2 to 3 gang conversion is.

 

[securespark]

So from this I take it that it is impossible to plug two 13 amp plugs into a twin socket.


And if each 13 amp plug had a 3 Kw radiant heater on the end it still only comes to 13 amps

Triple sockets are always fused? MK are but I don't believe to 2 to 3 gang conversion is.

No, it is perfectly possible to plug in two 13A plug tops simultaneously into a 2 gang socket.

No, the total load would be 26.09A.

Yes, they are fused, even the Convertas.

Felix - 2,5 is rated 28A.

 

[Damocles]

It is perfectly possible to plug two 13A plugs into a double socket, each drawing 13A. Only if you do the socket will melt, never mind the cable. Must be designed that way as a safety feature?