About Voltage Drop

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.

Why Voltage Drop Matters

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.

Factors Affecting Voltage Drop

There are four major causes of voltage drop:

• Wire Material: Copper is a better conductor than aluminum and will have less voltage drop than aluminum for a given length and wire size.
• Wire Size: Larger wire sizes (those with a greater diameter) will have less voltage drop than smaller wire sizes of the same length.
• Wire Length: Shorter wires will have less voltage drop than longer wires for the same wire size.
• Current Load: An increase in current through a wire results in an increased voltage drop.