What are the causes of voltage drops in house wiring?

Thomas Edison wanted to wire the United States for direct current (DC) but later admitted he was wrong. Alternating current (AC) used throughout the country lessens the problem of voltage drops in our electrical grids, including the wiring in our homes.

Definition

Voltage drop is the loss of voltage within a circuit due to resistance. The drop may be minuscule or significant, depending on the device the current supplies. Lights may be dimmer, motors work harder and more current is drawn to operate appliances.

Wire Length

All wire has resistance and causes a voltage drop. The longer the wire, the greater the drop. Long runs of wire over 100 feet may have significant voltage drop greater than five percent. The use of larger diameter wire in long runs helps reduce the amount of loss.

Poor Splicing

Splicing two or more wires by twisting them together creates a point of greater resistance than a straight wire. The voltage drop across a properly made splice is minimal, however a poor splice will cause a greater voltage drop. Using proper wire nuts and twisting clean wire ends together reduces splice voltage drops.

Terminal Connections

Receptacles, light sockets, fuses and circuit breakers are just some of the devices that have terminals. Poor terminal connections caused by oxidized wire, incorrect screw types and loose screws cause significant voltage drops. Clean oxidized wire ends and use brass screws fully tightened to make good connections.

Small Gauge Wires

The minimum wire size used in homes is 14-gauge wire for a 15-amp circuit. Using a smaller wire causes more resistance in the circuit which raises the temperature of the wire, causing even more resistance. The voltage drop through a too small wire is always significant. Use proper sized wires for all new circuits and replace old wiring that is inadequate.

Aluminum Wire

During a copper shortage, aluminum wire was and is still sometimes used. Connecting aluminum wire to copper wire or to a device not designed for aluminum wire causes significant resistance and voltage drop. Aluminum wire is safe if used properly and unsafe if used incorrectly.

Source:

Wiring Simplified 40th Edition; Richter, Schwan, Hartwell; 2002

More Information:

Home Wiring Hazards