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Wire Gauge, Resistance and Voltage Drop Calculation

Problem

I had an control system with 10 control stations. Each station required 24VDC power, with (-15%/+20% tolerance). Total current required was 23 Amps. My electrician wanted to power them up with single 24VDC power source. However, I did not know if the voltage drop over 1,000 ft wire would be too much. The table below is reproduced from data from American Electrician’s hand book .

Wire Size and Resistance Chart

Wire Size and Resistance Chart

Calculation

Minimum acceptable voltage to device is 20.4 VDC. If I can set the power supply to 26V, 6.6VDC drop over 1000 ft is still acceptable. With these two numbers, maximum acceptable resistance is 6.6V/23A = 0.287 OMG. From the chart, I have to use AWG 4 or above to connect the devices. With 0.2043″ conductor diameter, that’s a lot of wire to pull. It is much easier to pull 16 AWG AC wires for each node.

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