Voltage Drop

When voltage at the beginning of a length of cable/conductor (at the transformer) is higher than the voltage at the end, the difference is known as "voltage drop." Consequently, if the brightness of the lamps placed on a particular run is greater at the beginning of the system (closest to the transformer) than the lamps placed at the end of the system, then this is due to voltage drop.

Wires carrying current always have inherent resistance, or impedance, to the current flow. Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance (resistance).

A common analogy used to explain voltage, current and voltage drop is the infamous garden hose analogy. Voltage is compared to the water pressure supplied to the hose. The current is comparable to the water flowing through the hose, and the inherent resistance of the hose is determined by the type and size of the hose - just like the type and size of an electrical wire determines its resistance. The higher pressure and the larger size of the hose will allow water to flow more consistently. When the pressure is reduced and the hose diameter is smaller, less water reaches the end. Thusly, the water is more forceful nearest to the faucet and trickles at the end; a classic example of voltage drop.

Excessive voltage drop in a circuit can cause lights to flicker or burn dimly. This condition causes the load to work harder with less voltage pushing the current.

Voltage drop can be minimized through proper selection of the cable/conductor size between the transformer and first fixture based on the total wattage load and length of the run. We will explore other methods to minimize voltage drop later in this section.