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AC Voltage Drop Calculator

Calculate Voltage Drop

Use to quickly and accurately calculate AC voltage drop. The calculator uses the IEEE Red Book method of phasors instead of trigonometric approximations, greatly improving accuracy.

Calculation Inputs:

Voltage: The root-mean-square (RMS) voltage at the source of the circuit. Measured line-to-line for three-phase or line-to-neutral for single-phase circuits. Input range is from 1 to 1,000 V.

Current: Balanced line ampacity at the load. This value is the current at maximum load. Input range is from 1 to 1,000 A.

Power Factor: Power factor at the load. This is the cosine of the angle between the load voltage and the load current. Input range is from 0 to 1.0. 0 is purely reactive (an ideal capacitor or inductor) and 1.0 is purely resistive. Typical values for real loads are from 0.8 to 1.0.

Parallel Conductors: Identical sets of parallel conductors between the source and load. All parallel conductors are assumed to be the same size.

Length: One-way conductor length from source to the load. Input range is from 1 to 10,000.

Conduit: Conduit material impacts conductor reactance. Choices are Steel, PVC, and Aluminum. 

Conductor Size: Trade size of the current-carrying conductors (assumes the current is balanced). Used to look up the resistance and reactance for that specific conductor per NEC Table 9. Note: #12 aluminum resistance values assumed for #14 aluminum.

Conductor Type: Copper or Aluminum current-carrying conductors. 

Temperature: The ambient temperature in &degC. NEC Table 9 resistances are adjusted if the ambient temperature is not 75&degC.

Demand Factor: Load demand factor, an optional field. This value is used to scale the load current when calculating energy losses from the cable. Conductors are typically sized for the maximum load though average load may be less.

Calculating the expected voltage drop when sizing conductors is critical to ensure electrical loads have adequate voltage. Feeders are typically sized for no more than 2% drop and branch circuits for 3%. Conductors sized too large drive up construction costs and those too small will have excessive voltage drop.

I appreciate feedback; let me know how I can make the calculator better:

Thanks for your time! -Brendon Bruns