A load is any component in an electrical circuit that consumes power. It’s the part of the circuit that actually does something useful: a light bulb converting electricity into light, a motor spinning a fan, a toaster generating heat. Without a load, a circuit has no purpose. The load is the reason the circuit exists.
How a Load Works
Every circuit has three basic parts: a power source (like a battery or wall outlet), conductors (wires that carry current), and one or more loads. The power source pushes electrical energy through the conductors, and the load converts that energy into another form. A space heater converts it to heat. A speaker converts it to sound. An LED converts it to light.
The load also determines how much current flows through the circuit. A load with low resistance draws more current from the source, while a load with high resistance draws less. Think of it like a faucet: the load controls how freely electricity flows. This is why plugging in a high-powered appliance can dim nearby lights for a split second. The new load suddenly demands more current from the same source.
Three Main Types of Loads
Loads fall into three categories based on how they interact with the flow of electricity.
Resistive loads are the simplest. They convert electrical energy directly into heat. Toasters, incandescent light bulbs, and electric heaters are all resistive loads. Voltage and current stay perfectly synchronized, which makes these loads stable and predictable. Their power factor (a measure of how efficiently they use electricity) is essentially perfect at 1.0.
Inductive loads use coils of wire to create magnetic fields, which means they power things that spin or transform voltage. Electric motors, fans, and transformers are inductive loads. The magnetic field causes current to lag slightly behind voltage, which reduces efficiency. In industrial settings, this lower power factor can increase utility bills and even trigger penalties from the power company.
Capacitive loads store and release energy in electric fields. These are less common in everyday life, but capacitor banks are widely used in industrial power systems specifically to counteract the inefficiency caused by inductive loads. In capacitive loads, current runs slightly ahead of voltage, the opposite of what happens with inductive loads.
Calculating Load With Ohm’s Law
Three simple formulas let you figure out what’s happening at any load in a circuit. They all stem from Ohm’s Law, which describes the relationship between voltage (V, measured in volts), current (I, measured in amps), and resistance (R, measured in ohms).
- Voltage: V = I × R
- Current: I = V ÷ R
- Resistance: R = V ÷ I
To find the actual power a load consumes (measured in watts), you multiply voltage by current: P = V × I. So a device running on a 120-volt circuit and drawing 10 amps uses 1,200 watts. You can also calculate power if you know resistance: P = V² ÷ R, or P = I² × R. These variations are useful when you only have two of the three values.
Loads in Series vs. Parallel
When multiple loads are wired in series (one after another in a single path), their resistances add up. If you connect three loads with resistances of 10, 20, and 30 ohms, the total resistance is 60 ohms. The same current flows through every load, but each one gets only a portion of the total voltage. This is why old-style Christmas lights would all go dark when one bulb burned out: a single break in the series stopped current from reaching every other load.
In a parallel circuit, each load gets its own path back to the power source. The total resistance drops below the smallest individual resistance, which means the circuit draws more current overall. Each load receives the full voltage of the source, so they operate independently. Your home is wired in parallel. That’s why turning off the kitchen light doesn’t affect the living room TV. It also means each new appliance you plug in draws additional current from the same source, which is where overloading becomes a concern.
What Happens When You Overload a Circuit
Every circuit is designed to handle a specific maximum load. When you connect too many devices and exceed that capacity, the wires carry more current than they can safely handle. They heat up, insulation can melt, and in the worst case, a fire starts. The National Fire Protection Association reports that electrical failures and malfunctions cause roughly 47,700 home fires in the U.S. each year, resulting in 418 deaths, 1,570 injuries, and $1.4 billion in property damage. Overloaded circuits are a major contributor.
Warning signs that a circuit is overloaded include flickering or dimming lights, frequently tripped breakers or blown fuses, warm or discolored wall plates, buzzing sounds from outlets, and a burning smell near receptacles or switches. If you feel a mild tingle when touching an appliance or outlet, that’s also a red flag.
Circuit breakers and fuses exist specifically to prevent overloads from becoming dangerous. When current exceeds a safe threshold, a breaker trips or a fuse blows, cutting power before wires overheat. Arc fault circuit interrupters, a more advanced type of protection, can prevent an estimated 50% or more of electrical fires by detecting dangerous electrical arcs that standard breakers miss.
Common Household Loads by Wattage
To get a practical sense of how much load different devices place on your home’s circuits, here are some typical wattage ranges:
- Phone or e-cigarette charger: up to 65 watts
- Slow cooker: 75 to 250 watts
- Heated clothes airer (wire type): around 300 watts
- Dehumidifier: 150 to 350 watts for compressor types, up to 650 watts for desiccant types
- Air fryer: 1,500 to 2,600 watts
- Heated clothes dryer (pod type): 800 to 2,300 watts
A standard home circuit in the U.S. is rated for 15 or 20 amps at 120 volts, which means it can deliver 1,800 or 2,400 watts total. A single air fryer can consume most of that capacity on its own. Plugging a second high-wattage appliance into the same circuit is a common way to trip a breaker. Spreading heavy loads across different circuits keeps each one within safe limits.