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!!!!

 

[Deleted member 9648]

A poorly designed 32a ring can be loaded at more than 32a for a period of time before the OCPD operates.The only problem I can envisage with the scenario you describe is uneven loading of the ring circuit,with a possible considerable load at one point of the ring.That said as far as I'm aware there is no regulation preventing two spurs being wired from the same part of a ring.

 

[telectrix]

look in bgb. appendix 15. 1 single or 1 double socket on an unfused spur. asny more, fuse down with a FCU to 13A.

 

[Deleted member 9648]

look in bgb. appendix 15. 1 single or 1 double socket on an unfused spur. asny more, fuse down with a FCU to 13A.

The OP is referring to two sockets wired as separate spurs from a single point on the ring,not a spur from a spur.

 

[HappyHippyDad]

A poorly designed 32a ring can be loaded at more than 32a for a period of time before the OCPD operates.The only problem I can envisage with the scenario you describe is uneven loading of the ring circuit,with a possible considerable load at one point of the ring.That said as far as I'm aware there is no regulation preventing two spurs being wired from the same part of a ring.

Thanks Wirepuller,
Thats what I was thinking but what would actually be wrong with that? I suppose the more unbalanced a ring the closer you are getting to a single 2.5mm taking 32A? (I know thats virtually impossible, just looking at the extreme to try and understand if an unbalanced ring is dangerous)

look in bgb. appendix 15. 1 single or 1 double socket on an unfused spur. asny more, fuse down with a FCU to 13A.

This would only be 1 socket on an unfused spur Tel, just 2 of them on the same socket (i.e 4 conductors in live terminal of socket)

 

[Richard Burns]

This arrangement is OK, but as you say can tend to overloading at a particular point on the ring.
In reality the loading is not likely to be a problem unless these spurs are for water /air heating appliances.
You would still have to limit the maximum spurs to less than total points on the ring.
Normally the problem with two sockets spurred individually off a ring socket is space for the cables.

 

[kingeri]

I'd also consider taking two spurs from one point a bit of a bodge job, I mean how much harder than that would it be to extend the ring?

 

[Aindowsimon]

2 x 26 = 52
Not sure if I'm reading you're post correctly if you have 2 x 2g socket of an existing 2g socket that is 6 socket on 2 legs of a ring . I agree unless these sockets are in a busy kitchen it is unlikely to be pulling at high end of OCPD but we just don't as we don't know if these sockets will get used for something different in future witch could cause issue

 

[telectrix]

soz. misread the OP.

 

[HappyHippyDad]

This arrangement is OK, but as you say can tend to overloading at a particular point on the ring.
In reality the loading is not likely to be a problem unless these spurs are for water /air heating appliances.
You would still have to limit the maximum spurs to less than total points on the ring.
Normally the problem with two sockets spurred individually off a ring socket is space for the cables.

Thanks Richard,
I think I would only use it as a last resort then, so it will probably never occur. I had a bit of a practice with the crabtree 2g socket and was suprised when 4 x 2.5mm conductors easily fitted in!

I'd also consider taking two spurs from one point a bit of a bodge job, I mean how much harder than that would it be to extend the ring?

Yes, It does seem a bit of a bodge doesn't it, just not quite sure why. You're quite right, not much harder to extend the ring, I was just interested in the facts and figures.

 

[i=p/u]

Well I think it's wrong, by all means take from the spur but not into the same skt as 1st spur... But what do I know baby

 

[Des 56]

2 x 26 = 52
Not sure if I'm reading you're post correctly if you have 2 x 2g socket of an existing 2g socket that is 6 socket on 2 legs of a ring . I agree unless these sockets are in a busy kitchen it is unlikely to be pulling at high end of OCPD but we just don't as we don't know if these sockets will get used for something different in future witch could cause issue

Simon
I believe that most double sockets are rated for 20 amp continuous load only,they are not manufactured to be able to withstand a 26 amp load for a sustained period so are not rated as such

Add to that,the likelyhood of using a number of appliances in the same location that take anywhere near that load and the risks are reduced greatly

I agree,there are much better ways to make the addition,especially getting all your eggs in the one basket, but it may not warrant any code if it were an eicr

 

[HappyHippyDad]

Simon
I believe that most double sockets are rated for 20 amp continuous load only,they are not manufactured to be able to withstand a 26 amp load for a sustained period so are not rated as such

Add to that,the likelyhood of using a number of appliances in the same location that take anywhere near that load and the risks are reduced greatly

I agree,there are much better ways to make the addition,especially getting all your eggs in the one basket, but it may not warrant any code if it were an eicr

That was another question of mine Des. What is a socket rated at? A junction box is clearly rated. A socket is acting much the same as a junction box so it should have a clear rating. Sockets state on them 13A, but what is that referring to as they clearly take much more than 13A? What is its rating?

 

[alanclifton]

the socket may only be rated for 20a but the connection is external to the socket, therefore if the connections are tight the socket is not loaded

 

[Aindowsimon]

Simon
I believe that most double sockets are rated for 20 amp continuous load only,they are not manufactured to be able to withstand a 26 amp load for a sustained period so are not rated as such

Add to that,the likelyhood of using a number of appliances in the same location that take anywhere near that load and the risks are reduced greatly

I agree,there are much better ways to make the addition,especially getting all your eggs in the one basket, but it may not warrant any code if it were an eicr

I was quoting OP

 

[Aindowsimon]

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 might be misunderstanding this ?

 

[Des 56]

I was quoting OP

Understood

I was only making available some information I had read

 

[gazj82]

I changed a socket last week in a guys kitchen. It had three spurs off the ring in it! Five 2.5's do fit in a Crabtree socket, but by god did I swear! They all lunged out at me as I took the old socket off!

 

[Lucien Nunes]

They might physically fit, but can you trust the terminal to make secure contact to all conductors at the same time? I can think of situations with four or five cables in one hole, three were clamped but the others fell out. Not an ideal setup, you must have put in some effort to get it back together as I can imagine the original workmanship not being of the best.

 

[gazj82]

It took some doing, each conductor got a good tug before the socket got screwed back.

 

[electrician4u]

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!!!!

when did 26+26 start equalling 32? it's 52

 

[markc123]

when did 26+26 start equalling 32? it's 52

Edit.

 

[Des 56]

when did 26+26 start equalling 32? it's 52

Yes indeed, 52 is what I made it ,mind you the double digit adding was a bit taxing for me

I think he had in mind 32 amp circuit max rating

 

[markc123]

Mis-read the OP....can see how you've got the 52 now.

I just presumed in my brain the 32A rating.

Not to worry ladies and gents.

 

[electrician4u]

A 32A mcb doesn't act as a current limiting device! and btw, 52A would take about 10 minutes to trip a B type mcb and likely won't trip at all until about 47A being drawn, so the Regs say anyway.
don't underestimate the general publics' ability to abuse sockets. was called out to an office some time ago as they said their sockets were tripping to find a fan heater connected next to everyone's desk.they had 8 2kW heaters connected drawing 66A and the mcb still hung on for a few minutes after re-setting! in the last Regs you could spur off a spur but that's been changed obviously.

 

[DPG]

A 32A mcb doesn't act as a current limiting device! and btw, 52A would take about 10 minutes to trip a B type mcb and likely won't trip at all until about 47A being drawn, so the Regs say anyway.
don't underestimate the general publics' ability to abuse sockets. was called out to an office some time ago as they said their sockets were tripping to find a fan heater connected next to everyone's desk.they had 8 2kW heaters connected drawing 66A and the mcb still hung on for a few minutes after re-setting! in the last Regs you could spur off a spur but that's been changed obviously.

You could spur off a spur in the last regs ??? Daz

 

[Deleted member 9648]

A 32A mcb doesn't act as a current limiting device! and btw, 52A would take about 10 minutes to trip a B type mcb and likely won't trip at all until about 47A being drawn, so the Regs say anyway.
don't underestimate the general publics' ability to abuse sockets. was called out to an office some time ago as they said their sockets were tripping to find a fan heater connected next to everyone's desk.they had 8 2kW heaters connected drawing 66A and the mcb still hung on for a few minutes after re-setting! in the last Regs you could spur off a spur but that's been changed obviously.

You could spur off a spur in the last regs ??? Daz

maybe the last regs book he possessed was the 13th?

 

[markc123]

Haha, maybe wirepuller.

That's a interesting question to be fair. Whats the oldest copy of the regs anyone holds? Or do you just bin them?

I've got a shyte load of books in the attic...im a hoarder when it comes to electrical information and publications.

 

[Deleted member 9648]

Started with the 14th and always regretted binning it,would be an interesting read now.

(note to self...GET OUT MORE)

 

[Golden_Boy]

As there is no MINIMUM distance that sockets can be spaced on a rfc.then in practice you could have 2 literally next to one another and have one spur from each of them. 3 or 4 inches of cable in between. Satisfies the regs but in practice is exactly the same as having 2 spurs from one socket, Thinking about it it is worse as there are now 8 outlets available...

 

[Aindowsimon]

That's true about the whole RFC they are only 2 legs unlimited skts within permitted square meterage and one sper permitted to each , if those skts are deemed to be likely to supply a heafty loading surley the installation design is at fault and not RFC witch 9/10 will serve occupants more than adequately

 

[electrician4u]

You could spur off a spur in the last regs ??? Daz

used to be common practise

 

[scammell man]

BS7671 433.1.103 and appendix 15 page 425 (you have got one of these, haven't you?).

very self explanatory. Unfused spur = 1 cable + 1 single gang or 1 two gang socket.
Doesn't say you can't have 2 spurs from the same point. Selection and erection criteria will apply though.
If extending the ring be very careful you don't create a figure of 8!

 

[electrician4u]

BS7671 433.1.103 and appendix 15 page 425 (you have got one of these, haven't you?).

very self explanatory. Unfused spur = 1 cable + 1 single gang or 1 two gang socket.
Doesn't say you can't have 2 spurs from the same point. Selection and erection criteria will apply though.
If extending the ring be very careful you don't create a figure of 8!

doesn't seem very good practice though even if it is technically allowed.i've only ever come across it in BIY (bodge it yourself!) situations

 

[scammell man]

personally I think unfused spur in 2.5mm to a 2 gang is poor practice. Why not use 4mm?

 

[DPG]

used to be common practise

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

 

[telectrix]

personally I think unfused spur in 2.5mm to a 2 gang is poor practice. Why not use 4mm?

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.

 

[scammell man]

[/QUOTE] 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.[/QUOTE]

Then you would be in departure from BS7671 and lots of onus on you to show equivalent safety. Agree this is possible though.

I work on 2x13 A load continuous, 4mm should be good provided installed correctly, i.e. no serious down ratting factors applied. Now totally safe and no chance of thermal overload. I do not like cable rated below breaker rating in ANY situation.

 

[gazj82]

I work on 2x13 A load continuous, 4mm should be good provided installed correctly, i.e. no serious down ratting factors applied. Now totally safe and no chance of thermal overload. I do not like cable rated below breaker rating in ANY situation.

In theory it is limited by the fuses in the plugs that will go in the socket. In practice this sort of doesn't work because of unfused doublers etc.

A good example of where fusing down after a reduction in cable size does work is the old busbar chamber method. Tap off in smaller cables and switch fuse after the reduction. Just because the fuse is not immediately before cable reduction does not mean it's not protected.

 

[jamminuk]

Doing an EICR on a property and came to the kitchen, when i dropped the sockets my jaw also dropped, no end to end on the ring, one socket had the following spurred off of it - 3 double sockets, extractor hood, cooker ignition which then also had another socket spurred off that to feed a washing machine!!!! dropped another socket as looking for other leg of the ring to find a socket fed in 1.5mm!!! The guy has just had his kitchen fitted, looks all lovely and nice on the surface but really bad underneith. This was done by a Romanian builder who has no clue re electrics. I told the guy this needs to be sorted asap, i suggested he'll need a few fcus for the various spurs but it'll mean breaking a tile or two to put them in, cant really put any sockets below as cupboards already fitted, then try to find the other leg and put links between to make a complete ring, cant see any other way of doing it other then putting it on a 20A radial but that's not an ideal solution in my mind really, any other ideas? I thought you could only spur once off a socket unless you put an fcu then you can have as many as you like, didn't think you could spur out of a socket as many times as you can fit the cables into the terminal, doesn't sound like the right thing to do even if not in regs.

 

[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