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DC Voltage/Amperage/Wire Size/Distance
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dpilot83
Posted 7/28/2008 11:03 (#423446)
Subject: DC Voltage/Amperage/Wire Size/Distance



In order to enhance the reliability of the wiring on our planter and other equipment I'd like to do some checking on the size of the load in relation to the wire size that we're currently using. I found this pdf that gives a little bit of input on properly selecting wire sizes in regards to distance and I was wondering if it's accurate information.

Let's say you've got a 30 amp 12V DC pump and you're trying to decide if 12 gauge wire is large enough to run it 40 feet. According to said pdf, 12 gauge wire has 1.62 ohms of resistance for every 1000 feet. So for 40 feet:

40 ft / 1000 ft x 1.62 ohms = .0648 ohms of resistance for 40 ft of 12 gauge wire.

.0648 x 30 amps = 1.944 voltage drop over 40 feet.

(12 - 1.944) / 12 = 83.8% voltage at 40 feet. This represents a 16.2% loss which would be marginal at best. Am I understanding this correctly? If you get a size of wire that will provide only a 10% voltage loss over the distance you're planning on going, will that wire automatically be sized large enough to avoid frying the wire because of heating it up?

Where would I find information about resistance for larger sizes of wires? If I do that formula backwards trying to get a 10% voltage loss I come up with a resistance rating per 1000 feet of 1 ohm if I'm doing my math correctly.

Thanks. 



Edited by dpilot83 7/28/2008 11:04
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