Electrical
Electrical Voltage Drop Calculator
Voltage drop over a run, and whether it stays inside the 3% that branch circuits should hold to.
Result
A planning estimate, not a code calculation. Conductor sizing, overcurrent protection and load calculations are governed by the NEC as adopted and amended where you are, and by the listing of the equipment involved. Have the design confirmed by a licensed electrician and inspected. The 3% branch-circuit and 5% total figures are recommendations in NEC informational notes rather than hard requirements, though many local rules and specifications make them mandatory.
Get a Free Business AuditQuestions
About this calculator
Why multiply the distance by two?
Because the current travels out and back. The conductor length in the circuit is twice the distance to the load.
What does excessive drop actually cause?
Motors run hot and start poorly, heaters underperform, and LED drivers can behave oddly. It also wastes energy as heat in the wire.
Is 3% a legal limit?
In the NEC it appears as an informational note rather than a rule, but many jurisdictions, utilities and specifications adopt it as a requirement. Treat it as binding unless you know otherwise.
The formula
drop = 2 x K x amps x distance / circular mils, where K is 12.9 for copper and 21.2 for aluminium
Put this calculator on your site
Free to embed. Paste this where you want it to appear. It stays up to date automatically because it loads from BDEVY.
Please keep the attribution line. It is the only thing we ask in return.
Keep going
Related calculators
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.