Extending a ring, or a spur?

john4703 · 15 Jan 2020

I’m trying to work out how to add a double socket to a ring. I want to either spur off a surface mounted metal clad socket which is near the floor or extend the ring. It is in a church hall and the main reason to extend it is to allow for electric kettles and such to be easily used on tables as people tend to use extension leads which have all sort of dangers like tripping over them. I’d rather extend the ring as the power used on the new double socket will be fairly high. Two kettles will draw 6kw, about 26 amp, and I’d rather have plenty of capacity.

I am thinking of putting in a new metal clad double socket at tabletop height with a single length of 20mm plastic conduit linking the two socket boxes. Can I put a terminal block behind the existing socket and run three singles up to the new socket, and three singles down to the existing socket? All 6 singles would be in the same conduit. I could run two conduits but wonder why I would need to. The terminal block is accessible as it is inside the box, behind the socket. I’m sticking with metal clad as they are not perfect but do withstand the odd hit by a football better than plastic.

I suppose I am asking two questions.

1. Is it OK to extend a ring by using a terminal block inside the back box?

2. Is it ok to run both legs of a ring in one conduit?

DetlefSchmitz · 15 Jan 2020

I think the other question may be 'how much Public Liability Insurance do you have'. Whilst I would have no problem doing something like this in my own home, I would think twice about a church hall.

winston1 · 15 Jan 2020

Don’t run two kettles from a double socket. Double sockets are mostly rated at 20 amps not 26. Use two singles.

JohnW2 · 15 Jan 2020

winston1 said:
Don’t run two kettles from a double socket. Double sockets are mostly rated at 20 amps not 26. Use two singles.

We know that the BS1363 temperature rise test is conducted at 20A (although there's obviously nothing that says that a double socket must not be able to pass the test at higher currents!), but are there such products around whose documentation actually says that they are 'rated' at 20A?

Kind Regards, John

oldbutnotdead · 15 Jan 2020

All the above about PLI and working on non domestic installations.
Is the existing socket definitely on a ring final? Reason I ask- in churches where I've had to investigate the wiring (usually for running dimmer packs) the ones wired in the 60s and 70s tended to have not many sockets on MICC on radials fused to 20A. Usually beautifully done as well- lovely smooth curves and straight runs.
Operationally, get a Burco rather than using a load of kettles.
Electrically- if the existing socket really is on an RFC then you can add another socket to the ring. Use terminal block in the existing socket to link 1 incoming set with 1 outgoing set (to the new socket), the other incoming set stays in the existing socket with the return set from the new socket. Or just use 4mm singles up to the new socket.
4 x 2.5mm and 2 x 1.5mm in 1 20mm run is a squeeze but acceptable, for a short run like that neater and easier to use 2 runs.

john4703 · 16 Jan 2020

winston1 said:
Don’t run two kettles from a double socket. Double sockets are mostly rated at 20 amps not 26. Use two singles.

I agree but it is impossible to stop people doing so. It is better than using a 4 way extension and hoping the 13a fuse survives long enough for one of them to boil.
The PLI covers me doing "odd jobs" around the building and is for several million so I can risk that. I asked the insurance company may years ago.

JohnW2 · 16 Jan 2020

john4703 said:
I agree but it is impossible to stop people doing so. It is better than using a 4 way extension and hoping the 13a fuse survives long enough for one of them to boil.

You could perhaps go a long way to 'stopping them' by installing only single sockets.

Another possibility to consider might be to use 'modular' sockets. I've never looked into this but, given that each socket module surely must be rated for 13A, I would think that will more-or-less remain true when two are attached to the same faceplate.

Kind Regards, John

AndyPRK · 16 Jan 2020

use an MK.

Diversity - but I guess they will boil kettle after kettle. (although they will need refilling! so that's some off time)

JohnW2 · 16 Jan 2020

AndyPRK said:
use an MK.

It is what MK wrote (somewhere - but no-one seems to know where!) about their double sockets a long time ago that led to a lot of these "20A max" discussions ...

Some MK Technical Document said:
All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995 and are rated at 13A per unit. Double socket-outlets have been manufactured and tested to exceed this rating by margin that allows electrical safety and reduces the risk of heat and mechanical damage to components due to overloading. It should be noted that BS1363 part 2: 1995 does not allow double sockets to operate at twice the permissible maximum loading and it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time.

Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period. Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-outlet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire.

MK recommend that users of their sockets consult professional design Engineers when designing installations to avoid the possibility of heat and mechanical stress to components and installations caused by overloading of MK socket-outlets.

The Technical Data Sheets for MK double sockets have always said "13A per socket outlet" but, as I've reported before, even their Technical Support guys have told me that they are not sure what that is meant to mean!

The above test results obviously relate to pretty long periods of use.

Kind Regards, John

scousespark · 16 Jan 2020

Why can’t you put the table against the wall near the existing low level socket?

SUNRAY · 16 Jan 2020

AndyPRK said:
use an MK.

Diversity - but I guess they will boil kettle after kettle. (although they will need refilling! so that's some off time)

Why MK?
Are they supposed to be some holy grail or something?

In my rental properties I refuse to use them as they DON'T withstand 2x large loads, in fact in my experience the older Homebase DSSO's lasted longer at about 1/3 of the price.
As I sit here in my kitchen which we refitted some 12 years ago and spent a lot of money on a box of 10 MK DSSO's with neon and fitted 7 I see there is only one remaining, having used up all 3 spares, ie in 12 years we have had 8 failures, 9th was due to physical damage. As a comparison every socket in the house was replaced as we started decorating when we moved in 25 years ago and not a single one has been replaced since.

SUNRAY · 16 Jan 2020

john4703 said:
I’m trying to work out how to add a double socket to a ring. I want to either spur off a surface mounted metal clad socket which is near the floor or extend the ring. It is in a church hall and the main reason to extend it is to allow for electric kettles and such to be easily used on tables as people tend to use extension leads which have all sort of dangers like tripping over them. I’d rather extend the ring as the power used on the new double socket will be fairly high. Two kettles will draw 6kw, about 26 amp, and I’d rather have plenty of capacity.

I am thinking of putting in a new metal clad double socket at tabletop height with a single length of 20mm plastic conduit linking the two socket boxes. Can I put a terminal block behind the existing socket and run three singles up to the new socket, and three singles down to the existing socket? All 6 singles would be in the same conduit. I could run two conduits but wonder why I would need to. The terminal block is accessible as it is inside the box, behind the socket. I’m sticking with metal clad as they are not perfect but do withstand the odd hit by a football better than plastic.

I suppose I am asking two questions.

1. Is it OK to extend a ring by using a terminal block inside the back box?

2. Is it ok to run both legs of a ring in one conduit?

With all the usual caveats about safety, competancy and testing. My rule of thumb has always been 6x 2.5mm² singles is good to 2 straight lengths of 20mm tube , or 6m. Adding any bends halves the distance, ie 3m for first bend 1.5m for second. I haven't looked but I think the book shows something more than my figures.
My experience of public spaces points to using metal conduit and metal clad sockets, as you state 2 kettles I'd definitely go for 2 single sockets over a double.

john4703 · 16 Jan 2020

scousespark said:
Why can’t you put the table against the wall near the existing low level socket?

The leads on the kettles are too short to reach!!! I know but I am dealing with elderly ladies who know how to do it and I'm a silly young man who knows nothing about how they do things or about their aches and pains (as I am 72 I like the young part).
A twin socket in the higher position will be useful for many things, not just the kettles.

JohnW2 · 16 Jan 2020

john4703 said:
A twin socket in the higher position will be useful for many things, not just the kettles.

No doubt - but two single sockets in the same place would presumably be at least as useful?

Kind Regards, John

AndyPRK · 16 Jan 2020

"Why MK?
Are they supposed to be some holy grail or something?"

I thought I read on here they were likely to be rated at 13A x2
unlike other brands which were 20A

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Extending a ring, or a spur?

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