Radial circuit to workshops.

[Chris Bacon]

I've one workshop, with a 2.5 sq mm T&E from a 16A MCB in the consumer unit, running about 15m from there to where it goes in to the workshop to about 20m to a possible/proposed exit.

The reason I say a possible exit is that I have another outbuilding coming along, which will need power too.

IF I run further cable from the end of the workshop's radial to the new outbuilding, the maximum length of the radial will be about 30m.

The floor area of the workshop is about 12 1/2 sq m. The other outbuilding's floor area is say 29 sq m.

Machinery to be run is generally hand tools. Possibly a 2kW fan heater if it gets really cold. Plus LED lighting.

Does that work?

[Andy Burns]

Assuming the circuit is designed to deliver the full 3680W that a 16A breaker is rated for, then no, the voltage drop is going to get you, assuming lighting** is on the same circuit, you ought to have 4mm^2 at that distance, or drop it to a

10A MCB? [or just say sod it]

** yes we know it's probably LED lighting which won't care about voltage, but rules etc.

[John Rumm]

It works, although will be slightly out of spec on voltage drop... 2.5mm T&E drops 18mV/m/A - so at full load that will be 0.018 x 30 x 16 = 8.64V

Within spec for a power circuit (<= 11.5V) but not quite for a lighting one (<=6.9V). To make matters worse, that has not included the cable to the point of use in the new building.

However it also assumes operation at full load, which is possibly less likely. Note also the tighter limit on lighting circuit also matters less with LED lighting.

So for the stated use, it will be "ok", although a bigger cable would probably have been a better choice originally.

Chapter and verse on how to check: