voltage drop

byron · 29 Oct 2001

Using the same sort of cable one uses to plug a boat into a marina's 240 volt power supply. What would be the voltage drop over a distance of 300 yards? Would there still be enough power left to operate say a greenhouse heater of
say 600 watts ?

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chippie · 29 Oct 2001

I'm not an electrician, just a builder but know from experience that a long lead causes a voltage drop on things like power tools ,and 300 yards is a very long lead. In general the longer you go the fatter the lead will have to be. Why not ask your local electrician for his view ,giving him the wattage of the heater to estimate from.
Cheers.

Strathglass · 29 Oct 2001

Yes.
A greenhouse heater is less dependant on the actual voltage than say a welder or compressor.
If you used a 13 Amp cable you would not notice any significent effect on a 600watt heater, if it has a fan it may run slightly slower, it will give out slightly less heat.
Icould measure the resistance of my 30 meter extention later today and quantify the actual loss if you wish and post the answer tonight.

byron · 29 Oct 2001

Thanks Iain that would be most helpful. My boat is 300 yards or so from my house and I would like to put a greenhouse
heater in the engine room for the winter. I had hoped to just use regular extension cable of a fairly heavy calibre but light enough to be coiled away when not required during the rest of the year.

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Paulka · 29 Oct 2001

If the distance covered is 300m., and the wire is 1,5 mm2, the voltage drop should be approx. 20volts.
For such a distance, I would prefer a wire 2,5 mm2, which would reduce the voltage drop (assuming a 600w heater) to approx 12 volts.

Sorry, I'm european, thus think metric!
Could'nt find the SWG equivalent!

Paul

ToMo · 29 Oct 2001

Hiya Skip,
why not get your local tame sparks to put in a permanent underground cable connected to a all-weather socket closer to your boat? using the right cable (he'll know) you will have a much more useful facility, and increase the value of your property as a bonus.

ToMo

Guest · 29 Oct 2001

I have tried working at the end of the club jetty with anout 40m of extension and it was enough to dim the lights significantly and a fan heater did't run very well exept on low setting. Given the cost of that much copper wire have you thought about fitting a small desil heater instead, running cost on marine desil might be about the same and you get to use it whilst sailing! If you rig an auto fire extingisher above it addressess the safety point but remenmber electric heater can also go wrong and catch fire.

Roly, Voya Con Dios, Glasson, Lancaster

byron · 29 Oct 2001

Boat's fitted with heater and a 9.5 gennie. This is just to stop things freezing up in the winter if I am not around.

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Strathglass · 29 Oct 2001

Byron,
The total resistance of my 13 Amp, 30metre B&Q extention drum measured with both live and neutral in series gave a reading of 1.3 Ohms.

The resistance of 300yards (277 Metres) of the same cable will be 12 Ohms.

Assuming a pure resistive load, your 600 watt heater will draw a current of 0.4 Amps.

A voltage of 4.8 Volts will be developed across a resistance of 12 Ohms when passing a current of 0.4 Amps.

If you use a similar cable to that in my B&Q extention I would anticipate a maximum voltage drop of 5 Volts over a 300 Yard cable when loaded with your 600 watt greenhouse cable.

I doubt if you would even be able to notice this voltage drop.

Do use one continuous cable as any joins will potentially increase the resistance considerabely and could be dangerous in damp weather.

When measuring the 1.3 Ohms I had two 13 Amp plugs in series with the cable.

Iain Simpson

byron · 29 Oct 2001

WOW! and thanks for the very definative reply. All I need do now is find someone to supply me with 300 meters on a reel.
Off I go a'surfing to find a supplier.
Thanks for all your trouble it is appreciated.

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Strathglass · 29 Oct 2001

got mysums wrong

Your heater will draw 2.5 amps,
The voltage drop would be 30 volts.
You will require something like 2.5mm cable to reduce the drop to an acceptable level.
Sorry about that
Iain

philip_stevens · 29 Oct 2001

I was in City Electrical Factors (CEF) this afternoon and they had a watertight inline cable connector. Cable reels are usually in 100 metre lengths - though they can be obtained longer, at a price.
If you use 3 core flexible 1.5mm sq equivelant cable, the voltage drop per metre at 20deg C (according to ECSmith catalogue and to BS6862 ) is .0125 volts. 2.5mm sq cable would be about .0075 volts per metre.
1.5 mm cable is rated for about 12 amps, and 2.5 for about 21 amps.
So for a 600 watt heater, you could use 1.5mm cable.
If you intend to use a kettle while working on your boat, use 2.5mm cable. Tea at 300meres would get too cold!!

regards,
Philip

bedouin · 30 Oct 2001

Re: Lateral Thinking

The solution to your problem is quite simple. You need to transform the voltage to a higher level for the trip down the 300 yds and then transform it back down again.

As the voltage drop will be inversely proportional to the voltage, transforming it to say 10kV will reduce the transmission losses to virtually nothing.

Needless to say this should only be undertaken by someone suitably qualified to work with high voltage installations. DIY is definitely not recommended in this case. I cannot be held responsible for any injury caused

byron · 30 Oct 2001

THANKS! Ta-ever-so for all the useful replies. I am currently looking for a supplier who can sell me a continuous 2.5mm flexible cable of 250 metres in length. Yup! On measuring it the distance between my house and my boat is 245 metres.

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philip_stevens · 30 Oct 2001

If you cannot get the continuous length, you can do as I suggested and use inline waterproof (not as I said, waterTIGHT!!) connectors or square IP67 plastic boxes with water proof glands - again, all from electrical wholesalers.

If you use either connectors or box/glands, get some greasy cloth Denso Tape to bandage the whole connector or box/gland in.

regards,
Philip

regards,
Philip

philip_stevens · 1 Nov 2001

Byron,
While in CEF this morning, I asked about long lengths of cable. Over 100mtrs of flexible cable is difficult to obtain and at a premium, while 200mtr lengths of 2.5 Twin & Earth 6242Y are more obtainable. I have the remains of a real in my garage.
The inline connector is to IP68. That is submersible. The square JB is to IP67 - can be pressure hosed.
If you want any more information, send me a PBO personal email.

regards,
Philip

byron · 2 Nov 2001

Thanks Philip I found that 100m lengths were the norm so I have ordered 3 lengths together with the connectors they should be here any day now.

philip_stevens · 3 Nov 2001

Byron,
Glad to be of assistance.

regards,
Philip

regards,
Philip

byron · 3 Nov 2001

It all arrived yesterday and I asked my firm's handyman to connect it all up only to find only 150 metres had been delivered. I emailed the company complaining only to find that on my on-line order I had mistakenly typed 150 instead of 250. Still at least I got all the bits and bobs correct plus the various heaters. Excellent site www.tlc-direct.co.uk

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