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:
- (iV) Volts at Source (potential at the beginning of the circuit).
- (cL) Circuit Length
- (c) Current (amps flowing through the circuit)
- (g) Wire Gauge (choose from 1 to 40 gauge)
- (wT) Wire Type (solid copper, stranded copper, solid aluminum, stranded aluminum)
- (tR) Temperature Range: normal (77o - 121oF) or high (122o - 167o F)
- (p) Single or Three Phase
Voltage Drop(VD): The calculator returns the number of volts of reduction over the circuit due to line loss.
The Math / Science
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:
- VD = Voltage Drop
- K = K factor for materials
- P = Phase Constant
- L = Length of the wire
- C = Current
- A = Cross-section area of the wire.
The type of wire and temperature range are used to compute the K factor (Ohms - circular mils per foot).
- K = 11 for Solid and stranded copper in the normal temperature range
- K = 12 for Solid and stranded copper in the high temperature range
- K = 18 for Solid Aluminum in the low temp range, and K = 20 for Solid Aluminum in the high temp range.
- K = 19 for Stranded Aluminum in the low temp range, and K = 20 for Stranded Aluminum in the high temp range.
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:
- %VD = percent voltage drop
- iV = Initial Voltage at start of the circuit
- VD = Total Voltage drop over length of circuit
Usage
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.
Electrician Calculators
- Voltage Drop: This computes the voltage drop in volts and as a percentage over a length of cable (wire) based on length of wire, gauge, wire material, temperature range and phase.
- Wire Gauge Choice for Safe Voltage Drop: This determines the lightest gauge of wire that can be used over a run (circuit) that maintains adequate voltage.
- Circular Mils and Voltage Drop: This computes voltage drop based on wire diameter in circular mils instead of wire gauge.
- Electricity Usage Cost: This computes the cost of electricity for the use of a piece of equipment based on the power consumption rate, duration and cost of electricity.
- Electricity Consumption: This computes the amount of electricity consumed by an electrical appliance or motor over time.
- Rolling Offset: This computes the travel (T) and run (R) of a rolling offset used in conduit piping based on the offsets and angles.
- Diameter of AWG Wire: This provides the diameter of wire based on the American Wire Guide (AWG) gauge in mils and millimeters, and it also provide the cross-section area in square millimeters.
- P = V2 / R: This computes power (Watts) based on the voltage (V) and resistance (R).
- DC to AC Converter: Computes the approximate voltage of Alternating Current (AC) from the voltage of Direct Current (DC).
- Diameter to Circular Mils: Computed the circular mils of a wire and the cross-section area based on the wire's diameter.
Reference
- Handyman InYourPocket by (Young and Glover), 1st edition published by Sequoia Publishing of Littleton, Colorado (Page 213)