Apply for financingVoltage drop calculator
This voltage drop calculator uses K times current times one-way length, divided by circular mils. Single phase multiplies by 2. Three phase multiplies by the square root of 3. The wire size calculator result is the thinnest listed gauge that stays under the percent you allow.
Voltage drop
7.90V
Planning arithmetic with the K constants shown. It does not check ampacity, temperature, conduit fill, or the electrical code. A qualified person sizes the circuit.
How it works
The approximate formula is multiplier times K times amps times one-way feet, divided by circular mils. K is 12.9 for copper and 21.2 for aluminum, in ohm-circular-mil per foot. Those are planning constants, not a lab measurement of your cable. The multiplier is 2 for a single-phase round trip and the square root of 3 for three phase. Percent drop is the volts divided by the circuit voltage. The list of AWG sizes uses standard circular-mil areas. The suggested gauge is the smallest copper or aluminum area on that list that keeps the drop at or under your limit. It does not check ampacity, bundling, temperature, or the electrical code. A qualified person still sizes the circuit.
Formula
Percent = volts ÷ circuit voltage × 100. The circular mils required for the limit are that same formula solved for the area. The thinnest listed wire is the list entry with the smallest area that still meets it.
Example
Twelve AWG is 6,530 circular mils. The drop is about 7.90 volts, or about 6.58 percent. A 3 percent limit on this example needs a thicker listed wire, 8 AWG. That suggestion ignores ampacity. Do not treat it as a code answer.
Tips
The formula already includes the return path in the multiplier. Enter the distance from the source to the load once. Entering the round trip as the length double-counts the path.
Equipment
Shop equipment that needs a real circuit can still be an equipment financing request from $15,000 to $2 million. Dengaro does not design the wiring. The drop is a planning figure.
Important questions
It finds the listed AWG whose circular mils are the smallest that still keep the drop within your percent limit. If none of the listed sizes are large enough, it says so. Ampacity can require a larger wire than voltage drop does.
12.9 for copper and 21.2 for aluminum, in ohm-circular-mil per foot. They are the constants in this approximation. They are not a measurement of a specific cable.
When the load is a three-phase circuit. The multiplier changes from 2 to the square root of 3. The voltage you enter should be the circuit voltage you are comparing the drop against.
It is the starting value in the field so you can see which wire meets it. Branch-circuit and feeder practices differ. This page does not apply a code article.
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