Circuit breakers are essential devices in the modern world and some of the most important safety mechanisms in your home. Whenever electrical wiring in a building has too much current flowing through it, these simple machines cut the power until the problem can be rectified. Without circuit breakers, household electricity would be impractical because of the potential for fires and other dangers resulting from simple wiring problems and equipment failures.

In this article, it will be explained how circuit breakers and fuses monitor electrical current and how these machines cut off the power when current levels get too high. The circuit breaker is an incredibly simple solution to a potentially deadly problem.

The power distribution grid delivers electricity from a power plant to your house. Inside your house, the electric charge moves in a large circuit, which is composed of many smaller circuits.

On one end of the circuit, the hot wire leads to the power plant. The other end, called the neutral wire, leads to ground. Because the hot wire connects to a high energy source, and the neutral wire connects to an electrically neutral source (the earth), there is a voltage across the circuit, and a charge moves whenever the circuit is closed. The current is an alternating current because it rapidly changes direction. 

The power distribution grid delivers electricity at a consistent voltage (120 and 240 volts), but resistance (and therefore current) varies in a house. Different light bulbs and electrical appliances offer a certain amount of resistance, also described as the load. This resistance is what makes appliances work. A light bulb, for example, has a filament inside that is very resistant to flowing charge. The charge has to work hard to move along, which heats the filament, causing it to glow.

Appliances are designed to keep current at a relatively low level for safety purposes. Too much charge flowing through a circuit at a particular time would heat the appliance's wires and the building's wiring to unsafe levels, possibly causing a fire.

This is where the circuit breaker comes into play. The circuit breaker's function is to cut off the circuit whenever the current jumps above a safe level.

How does a circuit breaker work?

Breaker Design: Basic

The basic circuit breaker consists of a simple switch, connected to either a bimetallic strip or an electromagnet. 

The hot wire in the circuit connects to the two ends of the switch. When the switch is flipped to the on position, electricity can flow from the bottom terminal, through the electromagnet, up to the moving contact, across to the stationary contact and out to the upper terminal.

The electricity magnetizes the electromagnet. Increasing current boosts the electromagnet's magnetic force, and decreasing current lowers the magnetism. When the current jumps to unsafe levels, the electromagnet is strong enough to pull down a metal lever connected to the switch linkage. The entire linkage shifts, tilting the moving contact away from the stationary contact to break the circuit. The electricity shuts off.

More advanced circuit breakers use electronic components to monitor electrical current levels rather than simple electrical devices. These elements are a lot more precise, and they shut down the circuit more quickly, but they are also a lot more expensive. For this reason, most houses still use conventional electric circuit breakers.

All the wiring in a house runs through a central circuit breaker panel. A typical central panel includes about a dozen circuit breaker switches leading to various circuits in the house. One circuit might include all of the outlets in the living room, and another might include all of the downstairs lighting. Larger appliances, such as a central air conditioning system or a refrigerator, are typically on their circuit.

Agrinet stocks a range of circuit breakers. For more information on the range, please contact Agrinet;

Samrand: T: 012 657 2222, E: enquiries@agrinet.co.za 

Bellville: T: 021 959 5420, E: belbestel@agrinet.co.za 

Or view the product online HERE.