Free tool
Voltage drop calculator
Enter the circuit and see how much voltage is lost on the way to the load,
in volts and as a percentage, plus the smallest conductor that stays inside your limit.
Measure the length one way, from the panel to the load. The calculator
doubles it for a single phase circuit.
0.00 V lost
Enter a circuit
How this is calculated. The calculator uses the standard resistance method with
K as the resistivity of the conductor at 75 degrees C, 12.9 for copper and 21.2 for aluminum,
and CM as the circular mils of the conductor.
What the code actually says. The NEC does not set a hard limit on voltage drop for
most circuits. The informational notes to 210.19(A) and 215.2(A) recommend no more than
3 percent on a branch circuit and no more than 5 percent for feeder and branch circuit
together. Some jurisdictions and some equipment manufacturers are stricter, so check both.
What this does not do. It does not check ampacity, temperature correction, conduit
fill or the derating rules. A conductor that passes on voltage drop can still be the wrong
size for the load, so size for ampacity first and then verify the drop.