The Voltage Drop calculator computes the reduction in volts over a run of wire (line/circuit) based on the length of the run, composition and size of the wire, the current, temperature range and phase.
INSTRUCTIONS: Choose units and enter the following:
Voltage Drop(VD): The calculator returns the number of volts of reduction over the circuit due to line loss.
It is important to select the correct gauge of wire for a circuit. 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.
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.
To compute percent voltage drop:
%VD = (iV -VD)/iV
where:
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.