Wire Length Calculator
Quick Overview
As electric current flows through wire, there is a loss in voltage. This loss is referred to as IR voltage
drop. Voltage (Drop) = Wire Resistance X Amps of current (E=IR)
Calculating the voltage loss for a pair of wires gets a little complicated, so we have constructed a quick look up table for what size wire you will need for your application. The table below is for 12-volt ac or dc devices only. You just need to know the power in Watts (VA), or Amps and the table will show how far you can go in feet for any size wire pair listed. The table is based on a 10% loss of voltage on a pair of wires. This should work for most 12-volt devices. Checking the manufacturer’s specifications, use the maximum watts or current and be sure the minimum operational voltage is 10v or below. The footage in the table is linear, a 20% loss would double the distance, or 5% would cut it in half. The table calculations are based on the ohms of the wire at 70oF. If the wire temperature is raised to 130oF the voltage drop would increase by about 3%. The voltage drop calculations are also based on a conventional load. If manufacturer makes recommendations for wire sizes, use them instead of this table.
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