Down load Windows Voltage Drop Calculator
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WARNING: The answers given by this voltage drop program only apply to conductor sizing to limit the voltage drop to a specific value. The actual conductor recommended by the voltage drop program might not be the sized required by the NEC for continuous loads, motor loads, terminal rating, ambient temperature, conductor bundling, etc. Be sure when sizing conductors you check the conductor size for voltage drop after you have determined the conductor required by the NEC. For more information on conductor sizing, click here.

Example: A 315 ampere, single-phase continuous load located 80 feet from the power supply must be supplied with a conductor not smaller than: 315 amperes x 1.25 = 394 amperes. This can be achieved by the use of two- parallel No. 3/0 conductors each rated 200 amperes. However for voltage drop considerations, only one No. 1/0 could be used! Naturally we must use two sets of No. 3/0, not one No. 1/0. Just be careful when sizing conductors.

Read: Voltage Drop Part ONE

Read: Voltage Drop Part TWO

Read: "5% Voltage Drop - a Closer Look"   Article from SureTest® - [MS Word™] - [PDF].