Fear of voltage drop!

[HappyHippyDad]

Its been along day, I've just finished off with looking around a big garden which has all sorts of electrical things going and would appreciate a bit of advice on VD.

Garden is supplied by 2.5mm SWA (buried), at present taking about 1000W from a 20A MCB in the garage CU. The chap wants 2 greenhouse fan heaters installed. The run is about 40m's in total.

Max allowable VD = 11.5
VD (mV/A/m) for 2.5mm = 18
length = 40m

so available power = (max allowable VD x 1000)/length x VD

= 16A (approx) = 3680W

Garden is already taking 1000W so I'm left with 2680W for 2 greenhouse fan heaters.

I have 2 questions:

1. Can anyone see a half decent greenhouse fan heater that is only 1.3kW?
2. Really, Really tired and just cant figure out if VD means the cable will be unsafe or the MCB more likely to trip.... ridiculous question I know but I've had a glass of port (yeah I'm ready for the jip :rolleyes2, I'm tired and I just want to figure it out. Quote doesn't even need to be done for a week!

 

[MDJ]

the fault current would be proportional to the voltage, so if the volts were down by 10%, then so would the fault current be 10% less. 900A as opposed to 1000A. don't think OCPD would be too bothered by that.

Yep ohms law, your right tel

 

[Hawkmoon]

the fault current would be proportional to the voltage, so if the volts were down by 10%, then so would the fault current be 10% less. 900A as opposed to 1000A. don't think OCPD would be too bothered by that.

Agreed - but I was talking about volt drop generally and perhaps more excessive than 10% - Just making the point that it may not only be the operation of equipment that you have to consider in these situations, especially if you are intending to 'non-comply'.