I am wiring 7 110v 16a industrial type sockets on a 50metres radial circuit for portable equipment protected by at the very most a 20a breaker fed from a 110v distribution board which in turn is fed from a double wound transformer centre tapped earth fault voltage no more than 55v.It is to be wired in swa xple cable but due to the absence of 110v tables in the IEE regs how do i work out sizing and volt drop i was going to use 2.5mm cable would this be ok?

Still need to be within the 4% allowance from the origin of the supply to the most remote outlet. Unless its extra low voltage then its outside the regs It does not matter what the applied voltage is you only need your design current and cable resistance.
Vd = I x R
R is a constant

Second that. When calculating the voltage drop, just remember that at 110V that's a maximum allowable loss of 4.4V, not the 9.6V you might have fixed in mind from 4% of 240V.

is it withi regulations to run a ring final circuit on 110v supply for workshop sockets.
its just i heared an electrician saying something about this, a couple of years back.

(7671 iee regs)

Another question, slightly off topic. Is 110V a nominal or median voltage and what is the voltage tolerance allowed in these systems. My question stems from the fact that the UK has a nominal domestic voltage of 230V but in reality it is 240V – and from previous posts on the subject, sometimes higher.

jamesS I cant see any problems with a ring circuit for 110v sockets as long as you keep to the parrameters as laid down in 7671 regardig area to be supplied. I think I would probably restrict the CPD to 20 amps as well. outlets are only going to be for convienience I presume. Bet paul Uk will ahve somthing to say on the subject of the dreadedring though

Hutch, We in the uk would class 110v as low voltage, same tolerance applies 4%, as paul said earlier just have to watch the figures it works out as 4.5v max for voltage drop. Re your question about 230v yes its our nominal domestic voltage but it still comes into the category of low voltage. Kind of confusin aint it!

I was under the impression that 16a industrial sockets [Bs En 60309 ] could only be wired on a radial circuits we use them all over our site which is a large engineering workshop for all sort of applications such as drills ,heat guns , ,conduit threaders,hoovers etc they are usually a permanent fixture coloured yellow for 110v [manufactured by cee-form or mennekes] The low voltage is for the users safety and as they are not fused they rely on the trip back at the board usually a 20amcb which i think is equivalent to a 13a fused plug it can also incorporate a rcd device to trip at 30ma for extra safety The drawback is when a number of devices are plugged in it is easily overloaded and you have to feed some of them from a different any area but we are told this is how its designed for safety.If They were on a Ring main somebody could easily put in a 32a breaker thinking it was like a domestic ring main maybe causing problems if a fault occured and the breaker to high to trip

Justajiffy, I agree with you if your going to be using these over a very wide area in a work shop. I did qualify my thoughts with use for convienience.By that I mean to keep trailing leads to a minimum etc. Cant realy see that your any better off with your 50meter radial though with seven sockets on it!

Me? Have an opinion on ring circuits? I wonder what gave anybody that idea!

The problem is that the OCPD needs to be limited to around 20A to afford proper protection for the tools/cords connected to the outlets. So if you have the same number of outlets in the same positions on a 20A ring or a 20A radial, you'll still have the same potential problems with overload and tripping.

The only real way to reduce this as I see it is to increase the number of circuits and lay them out to minimize the chances of heavy loads being on outlets on the same branch simultaneously.

you should use double pole mcbs,

Good call paul forgot that one, did get caught out once by some one only installing single pole mcbs on TX made me jump a bit.