178m sq floor area for socket outlets

Geordielad · Mar 7, 2011

Hi all this is first time I've posted so appologies if I've missed anything out.

Recently just done a i&t and the ring main in one part of the commercial building is completely "ballsed up" to say the least. Spurs off spurs with rings of them and even more spurs off them. Going to have to rewire the ring main.
Only problem is floor area for room is 178m sq. The ring main will be fed by an old bs3871 dorman smith 30a mcb. Type 3 i believe. So needs to be very low zs values.

I know regs say max floor area is 100m sq but with calculations you can have bigger area.
Would a 4mm ring main be ok for this area?
Or would it be best to split it up into separate radials?
Most of the pcs are fed by separate ring so will only be powering few printers an pcs an odd heaters.

I don't have any spare ways on distribution board so if poss will have to keep on the one mcb.
Cables will be run up 1m of trunking then across suspended ceilings.

All your help is much appreciated
Cheers

Deleted member 26818 · Mar 7, 2011

4mm² conductors, or even if neccessary 6mm² conductors.

malcolmsanford · Mar 7, 2011

You are going to have to put your designer hat on here. The sq metre a guide is within a guide and should be dealt with as such, you can have a RING FINAL CIRCUIT of any sq area providing you design it correctly. The major priority for you would be the VD on such a Ring final.

As Spin as indicated you could wire the ring in 4mm or 6mm, if you do decide 6mm is ok then it may be best to wire the 6mm legs into an adaptable box then a single 4mm into the socket if they are going to be BS 1363 socket outlets.

Personally as you have no spare ways in the board I would look at fitting a smaller say 4 way DB. You could either supply this from the old 30amp BS 3871. It will depend on the type of loads that will be utilised in the area, as you say it is commercial you may need to upgrade the 30amp to a 40amp MCB. If it is expected to be a heavier load, then you may be able to supply it another way, perhaps off the existing boards supply.

By fitting a newer DB though will give you much more flexibility in designing a sub installation feeding this area.

Geordielad · Mar 7, 2011

I was hoping to not have to get out my designer hat in the off chance some one has come across similar issue in past. The client wants me to do it the cheapest way possible.

Think I'll just fit separate board next to original one to feed ring mains an split it up that way.

6mm in sockets is too much trouble for my liking!! Never again after having to get a 90mm 4 core swa into isolation box Designed for 50mm 4core swa.

Cheers for your help everyone