A load is any component in a circuit that consumes electrical energy and converts it into something useful, whether that’s light, heat, motion, or sound. A light bulb, a toaster, an electric motor, and a phone charger are all loads. Without a load, a circuit has no purpose. The load is the reason the circuit exists.
How a Load Works in a Circuit
Every circuit has three basic parts: a power source (like a battery or wall outlet), conductors (wires), and a load. The power source pushes electrical current through the wires, and the load resists that flow while converting the electrical energy into another form. An incandescent bulb converts it to light and heat. A speaker converts it to sound. A motor converts it to spinning motion.
The load is also what determines how much current flows through a circuit. A load with high resistance draws less current, while a load with low resistance draws more. This relationship follows a simple rule: voltage equals current multiplied by resistance (V = I × R). If you know any two of those values, you can calculate the third. For practical purposes, the power consumed by a load is measured in watts or volt-amperes, and you can find the current draw by dividing the load’s power rating by the voltage. A 1,200-watt hair dryer on a 120-volt circuit, for example, draws 10 amps.
Three Main Types of Loads
Resistive Loads
Resistive loads convert electricity directly into heat or light. Incandescent bulbs, toasters, space heaters, electric stoves, and water heaters all fall into this category. They’re the simplest type of load because current and voltage rise and fall together in perfect sync. This gives resistive loads a power factor of 1 (called “unity”), meaning all the electrical energy delivered to them gets converted into usable work with no wasted reactive power.
Inductive Loads
Inductive loads use coils of wire to create magnetic fields, which then produce motion or transfer energy. Electric motors, fans, compressors, transformers, and fluorescent light ballasts are all inductive loads. Because these devices store energy temporarily in their magnetic fields, the current peaks slightly after the voltage during each cycle of alternating current (AC). This lag between current and voltage is called a “lagging power factor,” and it means the circuit has to carry more total current than what’s actually doing useful work. The bigger the lag, the less efficient the power delivery.
Capacitive Loads
Capacitive loads store energy in electric fields rather than magnetic ones. They’re less common in everyday life but show up in certain power supplies, LED driver circuits, and power factor correction equipment. In a capacitive load, current peaks before voltage, creating a “leading power factor.” Engineers sometimes add capacitive elements to circuits with heavy inductive loads to bring the overall power factor closer to unity, reducing wasted energy.
Linear vs. Non-Linear Loads
Loads can also be classified by how cleanly they draw current. Linear loads, like traditional motors and incandescent bulbs, draw current in smooth sine waves that mirror the shape of the voltage wave (even if they’re slightly out of phase). Non-linear loads distort the current wave into irregular shapes. Computers, LED drivers, variable-speed motor drives, and most modern electronics are non-linear loads.
This matters because distorted current flowing through a circuit’s wiring creates voltage distortion throughout the system, known as harmonics. The more non-linear loads on a circuit, the more voltage distortion builds up. Harmonics can cause excess heat in wiring, interfere with sensitive equipment, and reduce the lifespan of other devices on the same circuit.
How Loads Behave in Series vs. Parallel
When loads are connected in series (one after the other in a single path), the same current flows through each one. Their resistances add up directly: two 100-ohm loads in series create a total resistance of 200 ohms. Higher total resistance means less current flows from the source, so each load receives less power. Old-style Christmas lights worked this way, which is why one burned-out bulb could kill the entire string.
When loads are connected in parallel (each on its own branch between the same two points), each load gets the full source voltage independently. The total resistance of the circuit actually drops below the smallest individual load, because the current now has multiple paths to follow. More parallel loads means more total current drawn from the source. This is how your home is wired: every outlet and light fixture operates on its own parallel branch, so turning off one device doesn’t affect the others.
What Happens When You Overload a Circuit
Every circuit is designed to handle a specific maximum current. When you connect too many loads, or loads that draw more current than the wiring can safely carry, the circuit becomes overloaded. The wires heat up because they’re forced to carry excess current. In a properly protected circuit, a breaker trips or a fuse blows to cut the power before damage occurs.
If that protection fails or is bypassed, overheating wires can melt their insulation and start electrical fires. Even short of that extreme, overloading causes voltage drops that can damage sensitive electronics or make motors run inefficiently. This is why high-draw appliances like electric dryers, ovens, and water heaters are typically placed on dedicated circuits with heavier wiring and higher-rated breakers.
Electronic Loads for Testing
In engineering and manufacturing, electronic loads are specialized instruments used to test power supplies and batteries. A simple resistor can act as a basic test load, but it only simulates one fixed condition. An electronic load can be programmed to mimic the complexity of real-world usage, combining resistance, inductance, and capacitance that change dynamically. This lets engineers see how a power supply responds to sudden spikes in demand, fluctuating conditions, or the specific load profile of the device it will eventually power.