Extend RFC to a detached building/garage/shed?

[Spoon]

You brainy guys may be able to help with this thought I was having.
There has been a thread recently about 4mm radial from ring main.

This got me thinking..... (No funny comments)
So my question is: If you had a building/garage/shed, say about 5 meters away from a house, is it acceptable to extend one of the RFC's to this building?

I know its best to have it's own circuit, but just for this conundrum lets say there are no spare ways in the CU.
Yes you could use a 13A fused spur, but what if you wanted to have a few appliances in there that would draw more than 13A.

You would also be within the 100m area as well.

 

[Strima]

Nothing to stop you from doing it, not ideal though.

 

[Spoon]

Nothing to stop you from doing it, not ideal though.

Totally agree mate, its not ideal.
I was just thinking of different ways of doing things. Never thought of extending a RFC to something what was not part of the house.
It's something that I have not read about on here... That's why I asked.

 

[pc1966]

Agreed. So long as the cables are suitably protected, the only real down-side is the lack of fault separation, or having an independent means of isolation.

 

[Pete999]

You brainy guys may be able to help with this thought I was having.
There has been a thread recently about 4mm radial from ring main.

This got me thinking..... (No funny comments)
So my question is: If you had a building/garage/shed, say about 5 meters away from a house, is it acceptable to extend one of the RFC's to this building?

I know its best to have it's own circuit, but just for this conundrum lets say there are no spare ways in the CU.
Yes you could use a 13A fused spur, but what if you wanted to have a few appliances in there that would draw more than 13A.

You would also be within the 100m area as well.

Extend the RFC in 2.5MM2 no point in changing cable size half way through a circuit, no point whatsoever

 

[Dustydazzler]

you could extend the ring to an outside building , but I personally wouldn’t do it this way...

 

[telectrix]

the problem with doing that, if unfused, is that although the 4mm cable may be OK for 32A, you're running the risk of taking 32A from 1 point on the RFC. this is the whole capacity of the RFC without other outlets being considered, and, if the point where it's tapped off is close to 1 end of the RFC, then almost all of the 32A would be carried by the short leg. best to fit FCU and use 2.5mm cable for the spur, or redesign to provide a separate circuit.

 

[Spoon]

I was just thinking of, is it acceptable to extend the RFC using 2.5mm to another building close to the house, like a garage/shed. Then the RFC is also in there for the appliances.
So basically use 5 core SWA cable from socket in house to outbuilding. It's still a ring... but extended.

 

[Pete999]

I was just thinking of, is it acceptable to extend the RFC using 2.5mm to another building close to the house, like a garage/shed. Then the RFC is also in there for the appliances.
So basically use 5 core SWA cable from socket in house to outbuilding. It's still a ring... but extended.

The cpc wont be a ring though will it? 6 core maybe.

 

[telectrix]

The cpc wont be a ring though will it? 6 core maybe.

unless he uses 5 core SWA. 1 conductor and the armour for cpc?????

 

[Pete999]

unless he uses 5 core SWA. 1 conductor and the armour for cpc?????

Can of worms that one TEL

 

[telectrix]

yup. ? ? ?

 

[FatAlan]

I was just thinking of, is it acceptable to extend the RFC using 2.5mm to another building close to the house, like a garage/shed. Then the RFC is also in there for the appliances.
So basically use 5 core SWA cable from socket in house to outbuilding. It's still a ring... but extended.

Must admit that I have done this. Run a short section of 5C SWA from a metal clad garage socket a couple of metres out under a path and into a shed to another metal clad socket then continue the ring round the shed. CPC and armour all connected at each end of the SWA so end to CPC readings would be inaccurate and lower. If honest, not totally happy as ideally would be nice to be able to isolate shed. RFC in garage was small and not one of the main house circuits. Does anyone make a four pole isolate switch?

 

[pc1966]

Does anyone make a four pole isolate switch?

You could use a TPN style, though the majority are not switched-N. For 32A ring this would do:

32A TP+N Metal Isolator Switch Disconnector

With switched neutral, surface mounting in a metal enclosure

www.cef.co.uk

 

[Spoon]

The cpc wont be a ring though will it? 6 core maybe.

Glad you mentioned that mate. I was wondering if the earth had to be a ring as well.
All theoretical this anyhow, but I'm learning stuff, so all is good.

Regarding the isolation of the supply to the garage/shed, you could use a 4 pole changeover isolator. So in the 'off' position the garage/shed supply is isolated..

 

[Pretty Mouth]

The cpc wont be a ring though will it?

Would that matter? Assuming cpc meets adiabatic requirements throughout the circuit, and is taken to every point in the circuit?

 

[Spoon]

Would that matter? Assuming cpc meets adiabatic requirements throughout the circuit, and is taken to every point in the circuit?

This is where I wasn't sure so suggested a 5 core, hoping someone would correct me if I was wrong.

 

[pc1966]

Regarding the isolation of the supply to the garage/shed, you could use a 4 pole changeover isolator. So in the 'off' position the garage/shed supply is isolated..

That is a good point as you don't want the ring opened to isolate! Problem is many are centre-off which is not what you really want.

This might be usable (4P with NO/NC contacts), but you would need a separate box and knob to complete it. at 25A it ought to match the 2.5mm cable's rating:

CA20A223/GBA001*FT | Kraus & Naimer, 4P 2 Position 60° Double Throw Cam Switch, 25A | RS

uk.rs-online.com

 

[Pretty Mouth]

This is where I wasn't sure so suggested a 5 core, hoping someone would correct me if I was wrong.

I'm not sure myself tbh, which is why i worded it as a question. Have to check the regs. I was led to believe that a ring could be run in conduit or trunking, using containment as CPC, where there's no need for it to make a ring. Would the same not apply in this case?

 

[Spoon]

That is a good point as you don't want the ring opened to isolate! Problem is many are centre-off which is not what you really want.

This might be usable (4P with NO/NC contacts), but you would need a separate box and knob to complete it. at 25A it ought to match the 2.5mm cable's rating:

CA20A223/GBA001*FT | Kraus & Naimer, 4P 2 Position 60° Double Throw Cam Switch, 25A | RS

uk.rs-online.com

https://cpc.farnell.com/europa-components/lbc324p/isolator-change-over-32a-4p/dp/MC02638

This says its a 4 pole changeover isolator but the data sheet doesn't???? Or I'm tired and missing something.