2 spurs coming from the same socket - NOT a spur from a spur!

[HappyHippyDad]

Hello all..

I have recently added a spur for a customer and it got me thinking again about how many spurs could I actually take from the same socket!

The only socket I could use to take the spur from was on the ring and was already feeding a spur. Now I could have extended the ring but after a small amount of investigation I found that the existing spur was to a single socket hidden behind kitchen cupboards and never used so I disconnected and then fitted my spur.

It did make me think what was wrong with adding 2 spurs to the same socket though. The new socket was a crabtree and could easily accomadate 4 2.5mm conductors.

A double socket that is feeding a double socket spur has the (unlikely) potential to take 26A from the spur plus another 26A from whatever is plugged into it (therfore a maximum of 32A could flow through that one socket). By adding another spur to the socket the maximum it could take is not changed (still 32A).

I think the answer is that although possible its not a good idea to push the limit of a socket and by adding another spur I am pushing it closer to the limit of 32A more frequently which would be bad practice and unecessary as you can just extend the ring, but I'm thinking about it and need answers from the experienced chaps as otherwise I shall become frustrated!!!!

 

[tbs1983]

Yes Tel thats what I understand but what I was trying to say (maybe worded it poor) is that my tutor taught me you can't have 2 separate spurs off a socket - e.g. 4 x 2.5mm in a socket.

But you could spur off every socket on the ring if you want, but not 2 spurs off one socket. (By 2 spurs I mean 2 extra cables or radials added to a socket off the ring).

Whether he was right or not I don't know! I've always took it as gospel.

 

[Richard Burns]

He is simplifying things, the maximum number of spurs is equal to the number of point on the ring, therefore one spur per point on the ring. However it would also be possible (if the terminals permit the number of cables) to have half of the points on the ring with two spurs each and the other half of the points with no spurs.

This would not violate the number of spurs less than or equal to points in the ring, however because at a single point on the ring you can now have three outlets (the point on the ring and two spurs) drawing current and this could unbalance the ring loading and overload the cable, therefore to maintain the recommended equal load sharing around the ring it is better practice to spread out the spurs (or not have them at all!) around the ring.

But you can, with appropriate design of current use, have two spurs off one point on the ring without breaking any regulations.

 

[Guest111]

Re the debate on the maximum loading of a twin socket,IE whether it was 20 or 26 amps,I contacted mk tech department and this was their answer.

MK 13A Switchsockets comply with BS 1363: Part 2: 1995 British Standard Specification for Switched and Unswitched Socket Outlets.

BS 1363 requires that each individual outlet is subjected to various electrical tests, e.g. Switch Endurance at Rated Current, Socket Endurance at Rated Current, Switch Breaking Capacity at 1.25 x Rated Current, Socket Breaking Capacity at 1.25 x Rated Current. BS 1363 also requires that units are subjected to Temperature Rise assessment – Two Gang products are tested at 20A, (14A / 6A).

The British Standard committee consider that the above requirements are adequate for Household, Commercial and Light Industrial purposes.

 

[electrician4u]

Re the debate on the maximum loading of a twin socket,IE whether it was 20 or 26 amps,I contacted mk tech department and this was their answer.

MK 13A Switchsockets comply with BS 1363: Part 2: 1995 British Standard Specification for Switched and Unswitched Socket Outlets.

BS 1363 requires that each individual outlet is subjected to various electrical tests, e.g. Switch Endurance at Rated Current, Socket Endurance at Rated Current, Switch Breaking Capacity at 1.25 x Rated Current, Socket Breaking Capacity at 1.25 x Rated Current. BS 1363 also requires that units are subjected to Temperature Rise assessment – Two Gang products are tested at 20A, (14A / 6A).

The British Standard committee consider that the above requirements are adequate for Household, Commercial and Light Industrial purposes.

now it's clearer why in the regs they refer to socket outlets with a rated current not exceeding 20A. i'd often wondered what kind of s/o they were refering to as logically you'd expect a twin socket to be rated as 26A. think it should be written on the back as previously discussed

 

[electrician4u]

on the subject of 2 spurs off one socket, was looking through a Collins guide to electrical installation recently and they're adamant that you can only take 1 spur off 1 socket.i know that doesn't confirm anything but curious as to how they'd reached that decision