The Wire Gauge Choice calculator computes the lightest (highest number) gauge of wire for a circuit to NOT drop below a percent threshold due to line-loss over a circuit.
INSTRUCTIONS: Choose units and enter the following:
Wire Gauge (WG): The calculator returns the lightest (highest number) gauge of wire that will carry the current and NOT have a line loss of voltage greater that the user entered percent.
Lighter gauge wire is less expensive and often easier to work with. However, lighter gauge wire (higher numbered) can have an unacceptable effect on the drop of voltage over the length of the circuit. Maintaining voltage is important since many pieces of equipment will wear out more quickly if the voltage is below a margin which is often 5% or 10%. The factors in voltage drop include the length of the circuit, guage of wire, current (amps), wire type and material, temperature range and whether the circuit is single or three phase. This calculator lets the user specify these criteria and iterates through the characteristics of the wire gauges to find the lightest (highest guage) that sustains the voltage to within the required percentage drop. You could do this by hand, and compute the voltage drop for different wire gauges over the length you need, but this calculator does that for you rapidly.
This answers the question, "What gauge of wire do I need for my voltage not to drop more than 5%?" This formula returns the lightest gauge wire that does not exceed the voltage drop, and it provides the predicted voltage drop within the threshold. VIDEO INSTRUCTIONS
The Voltage Drop formula is:
VD = (K * P * L * C)/(A)
where:
The type of wire and temperature range are used to compute the K factor (Ohms - circular mils per foot).
The gauge is used to look up the wire cross-section area in circular mils. Phase is used to choose a phase constant (P), where P = 2.0 for single phase and P= 1.732 for 3 phase.
The user should measure the length of the run, and then choose the phase (single or 3), and the wire type and gauge. Pull-down menus are given for gauge, wire type, phase and temperature range.
The voltage drop can have an adverse affect on equipment. Typically, a 2% drop is the maximum acceptable drop in local use
Note that significantly higher volts can be used without affecting the voltage drop. This results in a lower percentage drop in comparison. For this reason, long lines from power stations to cities are typically in extremely high voltages and reduced for normal consumption via transformers after the distance has been run.