voltage drop

[byron]

Using the same sort of cable that one uses to plug one's boat into a marina's power supply. What would be the voltage drop if one had to take the lead say 300 yards to pick up 240 volts?
Woud there still be enough power left to run say a greenhouse heater of say 600 watts?

©2001
www.education-jobs.co.uk
www.alexander-advertising.co.uk

 

[Gludy]

It depends on the quality/size of the cable. A cable comes with the spec for what you lose per metre.
I had a mains cable to run (at my home) that sort of distance. You could not use a normal cable but had to use a fairly heavy duty cable that cost a lot and was heavy. The calculation is simple - just ask for the voltage drop per metre of cable then using watts = volts time amps you can see what power can be supported at the far end of the cable.

Paul

 

[Geoffs]

I expect you have 2.5mm2 cable for the usual 16amp marina supply. Such cable drops about 7.5mV for every ampere that flows for every metre of cable. Your 600 watt heater will draw about 2.5 amps from 240 volt supply.

So for 300 metres, remember - current has to go there and back, so 600 metres, a quick sum gives 11.25 volts drop. This means that the heater output will actually be about 550 watts. 300 metres is quite a long way, if you can’t use a shorter cable, then a heavier one would help. A 30 amp 6mm2 cable would half the losses.

That's all assuming my arithmetic is right!

 

[ToMo]

See my reply at PBO
ToMo

 

[byron]

Too difficult to put in a perm. run apart from which they want around £4-£5 grand. They say things like.. "you buy the cable and get the trench dug and we will connect it" I just wanted a firm to do it. Anyway its only for the very coldest days and I wouldn't want it there all the time... too many freeloaders around.

©2001
www.education-jobs.co.uk
www.alexander-advertising.co.uk

 

[ToMo]

I think I'll start a new business exporting Cornish sparkies to Oxon (?) at even half thoses prices I'll have my Colvic Watson in no time !

 

[KevL]

The sums look about right but I didn't get my calculator out.

11 1/4 V drop should be no problem at all, in fact you should get 600W output from them at that, the reason is simple. A few years back the UK had to "Harmonise" it's elec supply voltage with the rest of europe and an "euro average" voltage was chosen at 230V. Now to supply 230V from the national grid would have meant either changing all the sub stations or the generators at the power stations both of which would have been quite costly. So what did they do, they altered the tolerance on supply voltage and you still get 240V out of your sockets. BUT all new equipment is designed to operate at 230V +10% -5% (from memory) so with your volt drop you will be operating your heaters at the design voltage. Lucky old you.

Kev