Sockets on a radial circuit

Stephen-d · May 7, 2021

Hi all,

After some advice here to settle my mind, is there any regulations to limit the number of sockets on a 20A 2.5mm radial? Reading regulation 433.1 i know it states 50m² floor area, but i can't seem to find anything about the number of sockets? Or is it just the total load that determines this?

The reason is, i have been asked to install some sockets, 10 in total, for means of flexibility of plugging appliances in around the area, I'm being told that the sockets will be used for power tools, chargers, a computer and occasionally a heater.

Any information to help clear this up is appreciated.

littlespark · May 7, 2021

is that 10 x doubles?

realistically, they're not all going to be used at the same time? or is it something like a school workshop where several people will be working.

There must be a reason they give a floor area, rather than a number of points.... but it'll be down to the installer to know how many points for that area is being silly about it.

timhoward · May 7, 2021

Stephen-d said:
After some advice here to settle my mind, is there any regulations to limit the number of sockets on a 20A 2.5mm radial? Reading regulation 433.1 i know it states 50m² floor area, but i can't seem to find anything about the number of sockets? Or is it just the total load that determines this?

I think the only reference to 50 sq. m is in informative appendix 15 where it says "historically the floor area served has been limited to 50 sq m". So not a hard and fast rule and somewhat half-heartedly stated even there.
Total load is the main thing.
1 nail gun and a heater could make things interesting on a B16.
Are you at all tempted to do it in 4mm csa, just to leave it more flexible with loading?

westward10 · May 7, 2021

There is no restriction to the number of outlets you can put 500 on it if you wish.

Brian246 · May 7, 2021

It’s all just about suitability, if you think the demand won’t exceed 20amps then it’ll be fine, if not I’d probably split the circuit to two radials or upgrade to a 4mm. My personal take on the 50m2 rule is the cable length and potential volt drop? Correct me if I’m wrong though!

brianmoooore · May 7, 2021

IIRC. historically the max. area for 2.5mm2 T&E/20A MCB was 20m2. 4.0mm2 T&E/32A MCB was 50m2, and 2.5mm2 T&E ring was 100m2.

loz2754 · May 7, 2021

Stephen-d said:
Reading regulation 433.1 i know it states 50m²

Not in my book.

Stephen-d · May 7, 2021

littlespark said:
is that 10 x doubles?

realistically, they're not all going to be used at the same time? or is it something like a school workshop where several people will be working.

There must be a reason they give a floor area, rather than a number of points.... but it'll be down to the installer to know how many points for that area is being silly about it.

Yes doubles. No they won't be used all at the same time, i gather its just for ease of moving around and not using extension leads

Stephen-d · May 7, 2021

timhoward said:
I think the only reference to 50 sq. m is in informative appendix 15 where it says "historically the floor area served has been limited to 50 sq m". So not a hard and fast rule and somewhat half-heartedly stated even there.
Total load is the main thing.
1 nail gun and a heater could make things interesting on a B16.
Are you at all tempted to do it in 4mm csa, just to leave it more flexible with loading?

Yes 4mm did also cross my mind and possibly the better option i guess

Stephen-d · May 7, 2021

brianmoooore said:
IIRC. historically the max. area for 2.5mm2 T&E/20A MCB was 20m2. 4.0mm2 T&E/32A MCB was 50m2, and 2.5mm2 T&E ring was 100m2.

Sorry have i got this wrong? Im looking at appendix 15, is this the right place to look?

Stephen-d · May 7, 2021

loz2754 said:
Not in my book.

Sorry have i got this wrong? i am looking at appendix 15, is this the right place to look?

brianmoooore · May 7, 2021

I was referring to Edition 15, not appendix 15.

Stephen-d · May 7, 2021

brianmoooore said:
I was referring to Edition 15, not appendix 15.

Ah apologies, I was looking at the 18th edition

pc1966 · May 7, 2021

As above, you can put as many sockets on as you want. The fact you can does not mean you should!

Really it comes down to expected use/load. If most are phone chargers, etc, then 10 doubles sockets are no big deal, but if a large area than a RFC makes more sense, or going in 4mm radial, so 32A MCB is reasonable.

Stephen-d · May 7, 2021

pc1966 said:
As above, you can put as many sockets on as you want. The fact you can does not mean you should!

Really it comes down to expected use/load. If most are phone chargers, etc, then 10 doubles sockets are no big deal, but if a large area than a RFC makes more sense, or going in 4mm radial, so 32A MCB is reasonable.

Yea I understand that, since posting this and seeing the feedback I am favouring the 4mm radial, it is not a large area that it will be covering, I have been told there won't be any heavy loads its just the ease of having sockets in different locations. Thanks for your help ?

pirate · May 8, 2021

If you DID put 500 sockets in, you'd save on cable length...but your wrist would ache from making all the terminations...
and it would be rather more costly

Mike Johnson · May 8, 2021

For information only, the French Regulations allow twelve sockets on a 20amp MCB 2.5mm radial and eight on a 16amp MCB 1.5mm radial, a recent amendment to the regs was that a double socket counts as two, so prior to this you could have twenty four outlets on a 20amp 2.5mm.

brianmoooore · May 8, 2021

Mike Johnson said:
For information only, the French Regulations allow twelve sockets on a 20amp MCB 2.5mm radial

UK 20m2 (4m x 5m room). A room that size would have around 6 doubles, so not a great deal different.
I assume that if it's known that the sockets are going to be heavily loaded, then design considerations would override the general rule, just as in the UK.

Mike Johnson · May 8, 2021

Except for the amendment a couple of years ago where you could instal twelve doubles, forgot to mention the regs only allow for six sockets in a Kitchen above the worktop in 2.5mm, and appliance's have to be on their own 2.5mm 20amp radial.

Rockingit · May 8, 2021

The answer, I think, is more a practical one than theoretical - at some point you'll run out of allowable Zs!!

pc1966 · May 8, 2021

Rockingit said:
The answer, I think, is more a practical one than theoretical - at some point you'll run out of allowable Zs!!

From the OSG 4mm on 32A B is limited to 43m on VD (really 86m if loads are evenly distributed, as they probably would be with multiple sockets over a couple of rooms) and potentially much less on Zs (if, like me, you really don't like the idea of depending on the RCD for disconnection). Then it has 28m on TN-S typical max Ze

For comparison a RFC with 2.5mm on 32A B is 106m / 96m

For the OP's original 2.5mm & 20A probably around 84m on VD (distributed load) and 60-70m or so on Zs?

Rockingit · May 8, 2021

The true answer is provided in the Design Guide....

Stephen-d · May 8, 2021

Thanks for the information and help, the sockets won't be heavily loaded and not all used at the same time but just to be safe I think i am going to go with the 4mm radial ?

Dartlec · May 8, 2021

pirate said:
If you DID put 500 sockets in, you'd save on cable length...but your wrist would ache from making all the terminations...
and it would be rather more costly

Just been doing a loft extension with a client who really likes sockets.... A child's fairly normal size bedroom with 12 sockets - I think he wanted them near the bed, but couldn't decide where the bed was going!

Also 4 round pin sockets on the light circuit in the master bedroom, while will probably never get used....

I did put in 2 x 20A radials for 4 upstairs bedrooms when I might well have only gone with one in a 'normal' installation.

brianmoooore · May 8, 2021

If I could go back 40 years to when I wired my own house, each kid's bedroom would have been a separate 2.5mm2 radial. individual control over each room from the CU.

nicebutdim · May 8, 2021

Other than slightly increased initial costs, I can see only benefits to running several circuits where tradition might dictate that one would suffice.

Less inconvenience in the event of a fault. Less time involved in fault finding, should future issues arise. Reduced likelihood of a broken neck when extension leads are used in place of diagnosis and repair...

Dartlec · May 8, 2021

nicebutdim said:
Other than slightly increased initial costs, I can see only benefits to running several circuits where tradition might dictate that one would suffice.

Less inconvenience in the event of a fault. Less time involved in fault finding, should future issues arise. Reduced likelihood of a broken neck when extension leads are used in place of diagnosis and repair...

If AFDDs are required in AMD2 then I can see new builds going back to as few circuits as possible!