radial from ring main

[nick611]

hi there, would like your views on this.. Jb off a ring main and run two or three socket,s on a 4mm radial. I myself don,t mind it. no current capacity issues.and no zs problem,s if rcd protected.Any thoughts.

 

[chiplard]

You cannot do this.

If you intend to install multiple sockets spurred off a ring final circuit then you must install an FCU at the point of the spur.

 

[Risteard]

It could unbalance the ring.

 

[telectrix]

would be much better to run 2 legs in 2.5, and split the ring. then you would just have extended the ring. OK the thinking of load is not a problem, but it's not good practice. think of some poor spark might come along in a few years and think wtf is this

 

[mickytuff]

personally i would either fit an unswithed spur next to the ringmain socket (to protect the cable from overload) or i would extend the ringmain to include the additional socket/s, the latter would be more desirable, especially in a kitchen where the load would be higher than anywhere else in a typical house set up anyway, hope this helps.........

 

[malcolmsanford]

Or find 2 or 3 sockets on the ring and spur one socket off each. No need for 4mm^ cable either

 

[nick611]

not sure you all understood me.there are no overload problems because 4mm rated at 36amps.also the cable is stranded so no sparks would mistake it for 2.5..where are the technical problems with this?.

 

[Octopus]

I have to say I've always wondered why a fused spur has a limit of 13A, especially if you can add more than one socket and the cable will carry 20A!

Having a blonde moment!

 

[nick611]

balancing the ring is hilairious as well.no one can do that.we hav,nt a clue what the sockets we install will be used for.lets be honest

 

[rryles]

Isn't this shown as acceptable in 7671 appendix 15?

edit: I think the reason for fused spurs being limited to 13A is simply that you can only get FSUs and the fuses for them up to 13A.

 

[xraytek]

not sure you all understood me.there are no overload problems because 4mm rated at 36amps.also the cable is stranded so no sparks would mistake it for 2.5..where are the technical problems with this?.

I think the overload issue will be on the ring, if the additional radial is not at the midpoint.
If the radial is close to the CU then a large percentage of that current will take the short route and overload that part of the ring.

 

[nick611]

i must admit i would have no problems with this arangement. on an upstairs ring the total load would be very low.this would be ideal answer to roof conversion.one cable up, handfull of sockets in new bedroom.and as far as i can see no real reason not to do it.

 

[KFH]

The regs do not say you can do this. While you do not have to follow the regs you do have to be able to justify your decisions if something goes wrong. If you were feeding an attic conversion the regs would allow a FCU and then wiring in 1.5 T&E on the radial.


Yes it could unbalance the ring. With sockets on the ring it would be difficult to exceed 26A on any double socket; with the unfused spur you could have a max of 26A on each double socket on the spur, whether this would cause an overload problem on the shorter part of the ring is beyond my desire to calculate and that level of loading would be unlikely.


Not something I would do but I am not sure I would lose much sleep about it if I found it on an installation. Flag it up as a non compliance?

 

[dansk]

Its a spur of a spur, its shouldnt be done without FCU if your wanting to make it a radial of the ring - your call buddy, but if you dont follow the big red book and theres ever a problem, its you who has to justify your actions.....

 

[NMc]

You need to look at appendix 15 again. Page 362 is for ring main circuits. There is no mention on the diagram of what you intend

 

[jaresquire]

I think it's more a bad practice thing, can't think of the downside compared to a true ring except for testing and it's not the worst real world crime you find in most domestics of some age.
Wouldn't do it by design thou.

 

[chiplard]

IT IS NOT ALLOWED IN ACCORDANCE WITH BS7671!!!

END OF!!

It worries me when people come out with excuses as to why it wouldn't be a problem. Irrespective of how safe people think it is, what current might flow, what the load is etc etc. It is not an allowable method.

What else would people do in their own judgement of what is safe?

 

[jaresquire]

Ok, had a bit of a read of the brb, the issue seems to be;
Once the 4mm spur added, circuit is not a ring-final by definition, therefore need to be able to defend design, which is complicated because;
Need to consider the ring section as two conductors in parallel - requirements are balanced loading and no branches, so very careful examination of existing ring required.
Because of this I accept best to just extend ring or use fused spur.
Thats my humble pie for 2011

 

[marky sparky]

unfused spurs should only have 1 single socket running from them .ref 17 edition

 

[nickblake]

me i would stick a fused spur on it and wire in 1.5mm if its for just a couple of sockets in a bed room