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Electrikery help please


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I am preparing to install my rear winch in the RR. :D

As the cable runs are about 15' I am concerned about voltage drop over the run. Should I be?

I have searched t'internet but to be honest I don't really know what I am looking at. :lol:

So the real question is, what cross sectional area of copper wire should I be using for a 12V winch with a max theoretical current draw of 350A.

Come on, someone show me some formulae!

Ta muchly!

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When I ran the cabling to the rear winch I went for the biggest I could find at work. That happened to be 70mm2. No loss in power as far as I can see. Not that that hepls you much

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Bish....from another post I did

Mmmmm.......I'm using 70mm' Tri rated this time....when I get round to fitting the winches that is :unsure: ...although the cables are in already for them

Current carrying capacity

25 mm - 183 Amps

35 mm - 226 Amps

50 mm - 274 Amps

70 mm - 351 Amps

Roughly ..... for 90 oC Tri Rated cables degined to run hot

volts drop for those interested....

25 mm - 1.85 Mv/A/M

35 mm - 1.35

50 mm - 0.99

70 mm - 0.68

all these are Millivolts/per amp/per metre...

so for example....

70mm @ 0.68 Mv-A-M/ 300 Amps / 4 m cable run = 0.81 Volts drop

35 mm @ 1.35 Mv-A-M/ 300 Amp /4 m cable run = 1.62 Volts drop

this would be higher if your current draw is higher obviously

35mm @ 1.35Mv-A-M / 450 Amp / 4m Cable run = 2.43 volts drop

70mm @ 0.68Mv-A-M / 450 Amp / 4m Cable = 1.22 Volts drop

so your 12 volt winch with nominal 12 volts could only be getting 9.57 volts at the motor....using 35mm compared to 10.78 using 70 mm

obviously you will have hopefully a bit more that the nominal 12 volts available but after a fair bit of winching you may not , and its only for comparison


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Make sure the lugs are the correct size and crimped onto the cables using the correct pliers (cheap to hire from City Electrical Factors) other wise you will get massive voltage drop(and smoke :o ) at the cable ends.

The correct size luggs are also cheap from the electrical wholesalers :)

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