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

[electrician4u]

funny you should mention that. i was thinking along the same lines. it's like a reverse lollipop circuit. in effect the 4mm would give you a 32A capability on the spur, so theoretically you could add more than 1 outlet on the spur.

where does 32A come from?

 

[telectrix]

the 4mm on the spur can handle 32A, similar to 2 x 2.5mm if the rfc was extended. whereas a single 2.5mm is only good for 27A (clipped direct).

 

[electrician4u]

Not in the last regs though as the poster suggested. Daz

could have been thinking of socket fed from fcu and is actually still permitted in that circumstance. also can spur off a spur on a radial circuit, without fcu but only with 20A protection

 

[tbs1983]

I was taught in college you could only take one spur off any point of the ring. Fine to fuse down to 13A then have as many sockets in a radial spur as you want, but only ONE spur per ring socket.

Now after being taught that I always took it as gospel that it was a reg, although i've never looked it up.
But having read the above posts i'm wandering if my tutor was right or not?

 

[telectrix]

I was taught in college you could only take one spur off any point of the ring. Fine to fuse down to 13A then have as many sockets in a radial spur as you want, but only ONE spur per ring socket.

Now after being taught that I always took it as gospel that it was a reg, although i've never looked it up.
But having read the above posts i'm wandering if my tutor was right or not?

it's 1 outlet on an unfused spur off the ring, but if it's a fused spur, you can fit as many as you want.( within reason). see app. 15. bgb.

 

[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