4mm spurred from ring main

[Bradley6969]

32A ring main, adding 2 more sockets off this, spark I’m working with says add radial 4mm to 2 new sockets from ring I’m saying extend ring? I know 4mm can take 32A but I wouldn’t do it his way

 

[mydigitalhome]

Yes I would normally agree extend the ring, but, with limited infomation provided there could be a good design reason for that choice in that situation.

 

[Bradley6969]

Yes I would normally agree extend the ring, but, with limited infomation provided there could be a good design reason for that choice in that situation.

It’s in an industrial unit, the most plugged in will be a heater and drill chargers, and it’s not how I would extend doing his way that’s all

 

[Midwest]

App 15 gives recommendations on RFC & Radials, spurs etc.

 

[HappyHippyDad]

I agree with you, I don't think it is a very good idea. I expect it'll be fine and you'll never have any problems but you could say that about a lot of electrical work that is poor.

If this 'radial' extension of the ring circuit is at a point near the consumer unit or rather the beginning of the ring, then in theory the cable from the CU to this point could end up carrying more current than it's CCC and the 32A MCB may not trip. This is pretty unlikely but possible.

Also appendix 15 BS7671 does state that an unfused spur from a ring should only feed one single/double socket, although I am not sure how Industrial relates to BS7671.

lastly, I guess your friend is doing this because it is 'slightly' easier than extending the ring. In the future someone else may add to these sockets with more 4mm, due to the fact it is there and easy to spur from. Just because your initial work may not really be dangerous I think it's good to look ahead and think how your actions may affect future decisions.

 

[Zdb]

Deleted

 

[Lucien Nunes]

Non-compliant and would show up on an EICR.

I am not sure how Industrial relates to BS7671.

Same as any other installation. BS7671 covers everything from a flat to a nuclear power plant.

 

[Zdb]

Why not just have the two sockets on a FCU spurred off the ring if it's only for drill chargers?

 

[Lucien Nunes]

A heater is also mentioned, which will probably be at least 10A. The likelihood is that the total load would be maybe 10-15A which could result in a long, slight overload to the 13A FCU that will not blow the fuse. Although technically compliant, I would say this is bad practice for an industrial unit just to save a bit of cable. At our workshop two doubles would often get loaded to 30A total.

 

[Deleted member 26818]

Would have to be 6mm2, not 4mm2.

 

[Lucien Nunes]

How would 6mm² help?

 

[Deleted member 26818]

6mm2 would in most cases have a CCC greater than the rating of the protective device.
To be doubly sure use 10mm2.

 

[Wilko]

Hi - my 20p : when starting with a change that's more than one outlet I would extend the ring circuit or make a new circuit.

 

[gazdkw82]

If it's more than 1 spur (spurred socket outlet then another etc) then it will need to be fussed regardless of cable size

 

[Zdb]

Not if it's 6mm surely?

 

[gazdkw82]

It's a spur on a spur. I've never seen any documentation that says it's allowed if you use 6mm or higher.

 

[Wilko]

I think the design issue with adding an unfused radial at a point on an RFC is it's got the possibility to have a 32A point load. The 2.5mm ring is ok for 32A OLCP based on the load being reasonably distributed around it, which won't now be the case.

 

[Octopus]

Fused spur on ring, then as many as you like on the load side

 

[johnduffell]

Yes this ones been done to death, result is it's not a proper ring according to the informative appendix, but it can't cause an overload on the short leg as long as the joining point is more than iirc 15% of the way round the ring therefore it's ok in terms of minimise the chance of overload. Even with 2 double sockets near the end of a ring eg kitchen you could get overload so it's always a balance, just the 4mm spur stops the physical layout working in your favour.