AMO's Cable Calculator

Conductor Size & Voltage Drop Calculators
for Single and Triple Phase AC

 Available Cable Calculators
1ø VDSingle Phase Voltage Drop
1ø CSSingle Phase Conductor Size
3ø VDThree Phase Voltage Drop
3ø CSThree Phase Conductor Size
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 Formulas Used:
You can click on the different parts of the formulas below for an explanation of each variable.

Single-Phase Voltage Drop (VD):
VD = 2 × K × I × L

Conductors per leg × CMA

Single Phase Conductor Size:
Total CMA = 2 × K × I × L

Allowable Voltage Drop

Three-Phase Voltage Drop (VD):
VD = √3 × K × I × L

Conductors per leg × CMA

Three Phase Conductor Size:
Total CMA = √3 × K × I × L

Allowable Voltage Drop

Introduction to Cable Calculators

Todays motion picture equipment is more technically advanced than ever before.

Between solid state flicker free ballasts and electronic SCR dimmers, rigging a set with enough cable to stay within the 3% voltage drop (VD) of a main run (Feeder Circuit), and the 2% VD of a branch circuit allowed by The National Electric Code (NEC) has never been as important as it is now.

In a power distribution system, the Voltage Drop (VD) is the portion of the voltage lost during a particular run. It is important to know the VD of a run in order to ensure that we stay inside the Allowable Voltage Drop (AVD), as defined by the National Electric Code (NEC).

The AVD is 3% for a Main Circuit (aka: Feeder Circuit) and 2% for a Branch Circuit for a total of 5%. If your VD is greater than the AVD for the circuit type in question, you are not in compliance with the NEC standard. You will need to lower your VD, until you are compliant.

The calculators on this site will use the formulas shown to help you figure the Allawable Voltage Drop or Conductor Size in single phase (1) and three phase (3) AC.

In the formulas, we will use the letter "K" to represent Specific Resistance, which has a value of 10.8 when using copper conductors. "I" represents Amperage. "L" represents the Length of the run. CMA is the Circular Mil Area, or the cross section of the conductor measured in mils (.001 inch).

We hope you find these calculators helpful. Also feel free to check out for your portable power needs.

- Mike Amorelli & Associated Mobile Power, Inc.

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