load

A load is any device, component, or system connected to an electrical circuit that draws current and converts electrical energy into work, heat, light, or motion. In practical terms, the load is what your power source has to feed: a motor, heater, lamp, pump, or industrial machine. The load determines how much current flows through the circuit and what voltage drop occurs across the wiring and connections.

Loads fall into three broad categories based on their electrical behavior. Resistive loads, such as heating elements or incandescent bulbs, draw steady current proportional to the applied voltage; they consume real power only. Inductive loads, including motors, transformers, and solenoids, create magnetic fields and draw current that lags behind the voltage; they consume both real power and reactive power. Capacitive loads are less common in industrial settings but appear in certain control circuits and power factor correction systems; their current leads the voltage. Most industrial facilities contain a mix, with motors dominating the inductive share.

The load rating is critical for circuit design and protection. A motor rated at 5 horsepower at 480 volts, 3-phase draws approximately 6.2 amperes at full load current (FLC). Oversizing conductors and protective devices based on the actual load prevents nuisance tripping and voltage sag; undersizing them causes overheating and fire risk. Power factor, typically ranging from 0.7 to 0.95 for motors, affects how much apparent power (kilovolt-amperes) the load demands relative to real power (kilowatts).

Load variation and transient response

Most loads do not run at constant power. A pump slows under lower head pressure, a saw encounters dull or sharp teeth, an HVAC system cycles on and off. These variations mean the circuit must tolerate both steady-state current and brief inrush surges. Soft starters and variable frequency drives (VFDs) reduce inrush current on large motors from six to eight times rated current down to 2 to 3 times, protecting the supply and reducing mechanical shock to the driven equipment. Failure to account for transient loads has destroyed distribution transformers and tripped main feeders.

The term "load" also appears in mechanical contexts: the load on a shaft, bearing, or beam refers to the force or torque applied to it, measured in pounds, newtons, or foot-pounds. An electrical load and a mechanical load interact directly when a motor drives a pump; the pump's resistance is the mechanical load the motor must overcome, which determines the electrical current the motor draws from the circuit. Understanding both aspects prevents mismatches between motor selection and actual duty.