Voltage Drop Calculator

Estimate voltage drop for DC, single-phase AC, or 3-phase circuits

โšก

Voltage Drop Calculator

Estimate voltage drop, voltage at the end, and drop percentage using NEC data, estimated resistance by size, or custom resistance/impedance.

๐Ÿงฎ Calculator Inputs

V
Amps

๐Ÿ“Š Calculation Results

Voltage drop
0.80
volts
Voltage drop percentage
0.67%
Voltage at the end
119.2
volts

The calculation result is based on alternating current resistance and reactance data of 3-phase, 60 Hz, 75ยฐC from National Electrical Code (NEC). The actual voltage drop can vary depending on the condition of the wire, temperature, connector, frequency etc.

๐Ÿ”— Related Calculators

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Ohm's Law

V = I ร— R calculator

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Wire Size

Choose appropriate gauge

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Power

P = V ร— I calculator

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Resistance

Calculate resistance

๐Ÿ“š Understanding Voltage Drop

What is Voltage Drop?

Voltage drop is the decrease in electrical potential along the path of a current flowing in an electrical circuit. Excessive voltage drop can cause poor equipment performance.

5% Rule

It's recommended that voltage drop should be less than 5% under fully loaded conditions. This ensures proper equipment operation and energy efficiency.

Wire Selection

Proper wire size selection is crucial for minimizing voltage drop. Larger conductors have lower resistance and reduced voltage drop.

Voltage Drop Fundamentals

When electrical current moves through a wire, it is pushed by electrical potential (voltage) and it needs to surpass a certain level of contrary pressure caused by the wire. The voltage drop is the amount of electrical potential (voltage) loss caused by the contrary pressure of the wire. If the current is alternating, such contrary pressure is called impedance. Impedance is a vector, or two-dimensional quantity, consisting of resistance and reactance (reaction of a built-up electric field to a change of current). If the current is direct, the contrary pressure is called resistance.

Excessive voltage drop in a circuit can cause lights to flicker or burn dimly, heaters to heat poorly, and motors to run hotter than normal and burn out. It is recommended that the voltage drop should be less than 5% under a fully loaded condition. This can be achieved by selecting the right wire, and by taking care in the use of extension cords and similar devices.

Four Major Causes of Voltage Drop

  • Wire Material: Copper has better conductivity than aluminum for the same wire size
  • Wire Size: Larger wire sizes have less voltage drop than smaller sizes
  • Wire Length: Shorter wires have less voltage drop than longer wires
  • Current Load: Higher current increases voltage drop proportionally

Voltage Drop Calculations

Ohm's Law is the basic principle for calculating voltage drop:

Vdrop = I ร— R

For single-phase or DC circuits (accounting for round-trip distance):

Vdrop = 2 ร— I ร— R ร— L

For three-phase circuits:

Vdrop = โˆš3 ร— I ร— R ร— L