load voltage
The voltage that is able to be supplied by a power source to be consumed by the electrical load.
load voltage: what the source actually delivers
Load voltage is the voltage appearing across the terminals of an electrical device or circuit when current is flowing through it. It differs from the open-circuit or no-load voltage of the source because the source itself has internal resistance, and current flowing through that resistance causes a voltage drop. What matters in practice is not the ideal rated voltage of the supply, but the actual voltage available to do useful work at the load.
A simple example: a 12 V battery with an internal resistance of 0.1 ohms supplying 50 amps to a load will deliver only 12 minus (50 times 0.1) equals 7 volts across the load terminals. The voltage has dropped 5 volts inside the battery itself. This is load voltage: the real voltage that powers the motor, heater, or circuit, not the nominal battery rating.
In power supplies and generators, load voltage is typically lower than the rated voltage and drops further as load current increases. Designers must account for this when specifying components. A 24 V industrial control system might be rated at 20 amps, but if the supply has significant internal impedance, the load voltage could sag to 20 V or below under full load. This affects relay coils, solenoids, and logic circuits, which may malfunction if voltage falls beneath their minimum operating point.
Why this matters in the field
Load voltage is the reason why voltage is measured at the point of use, not at the supply terminals. A technician troubleshooting a failed motor controller should measure the actual voltage at the controller input, not assume the supply is correct. A 480 V industrial service may drop to 460 V or lower at the motor starter during heavy demand, especially in facilities with long cable runs or undersized distribution wiring. This voltage drop limits motor torque and can cause nuisance trips of protective devices.
The term is sometimes used interchangeably with terminal voltage, but load voltage specifically emphasizes that the measurement is taken while current is being delivered. Understanding the relationship between source voltage, internal resistance, current, and load voltage is essential for sizing power supplies, selecting voltage regulators, and predicting system behavior under real operating conditions.