Voltage Drop Calculator

This voltage drop calculator is a simple tool that helps you to determine the drop in the voltage at the end of the cable/wire during the transmission of power. Alternatively, you can use it as a cable/wire size calculator to decide the cable/wire and ensure the voltage drop doesn't exceed acceptable levels. The NY Engineer's Voltage Drop Calculator is designed for applications using AWG and KCMIL sizes.

Voltage drop is calculated using Ohm's Law

Vdrop = I X R

where:

It is important to note that the voltage drop formula changes depending on the number of phases in the circuit (single-phase or three-phase). In the following equations, the variables used are:

The formula for a Single-phase circuit :

Vdrop = 2 x R x I x L / 1000

The formula for a three-phase circuit becomes:

Vdrop = 1.73 x R x I X L / 1000

where:

R = Resistance of the conductor (ohms per 1,000 feet, or ohms / KFT)

I = Load current (amperes)

L = Length (feet)

If there is more than one set of conductors per phase, the calculation above must be divided by the number of set conductors per phase. Since resistance will be reduced by half, whenever the increase in the size of the cable does not reduce the voltage drop this increases the set of conductors method shall be applied.

Load Voltage - This is the voltage required for the load to operate. This shall be selected based on the supply & load voltage requirements.

If it is single phase supply with 2 Wire, Select – 120V 1ϕ

If it is single phase supply with 3 Wire, Select – 208V 1ϕ or 240V 1ϕ (As per utility)

If it is Three phase supply with 4 Wire, Select – 208V 3ϕ and so on

Conductor Size – This is the size of the electrical conductor that is planned to connect from the source to the load.

Conductor type – The type of conductor shall be copper or aluminum. Copper conductor is preferred based on the advantages of current carrying capabilities, but the cost is higher than aluminum. Depending on the budget, and availability users shall select this.

Number of Sets – This refers to the number of conductors (3 Phases + Neutral is one set for 3 phases, 2 Phases + Neutral is one set for 1 phase)

Conductor Length – Distance between the source to the load. That is a one-way distance only.

Load Amps – This is the full load amperage of the load. If not known breaker rating, amperage shall be selected.

Note:

1. The National Electrical Code (NEC) Articles 210.19(A): Conductors for branch circuits as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation. It is always preferable to limit the voltage drop to 3 Percent.

2. This equation assumes a power factor of 1.0, conductor temperature of 75°C, and individual conductors run in steel conduit.