Fire safety
Cable Voltage Drop Calculator
Long cable runs quietly eat your supply voltage - work out the loop drop before the end-of-line device browns out.
Calculator
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How it works
Copper resistance is about 0.0175 ohm x mm2 per metre. The loop is out and back, so R = 2 x length x 0.0175 / csa, and the drop is current x R. Keep it under 10% of supply and above every device's minimum voltage.
Frequently asked questions
How much voltage drop is acceptable?
A common rule for 12/24 V systems is 10% maximum - but the real test is the end-of-line device: a camera rated 11-13 V on a 12 V system leaves less than 1 V to spend.
Does doubling the cable size halve the drop?
Yes - drop is inversely proportional to conductor cross-section. Going from 0.5 mm2 to 1.0 mm2 halves it; so does halving the run or the current.