Whether you own a home or a commercial building, it relies on an electrical panel to distribute power. Most of them look like nondescript gray boxes mounted in some out-of-the-way spot. You’ve probably opened at least one electrical panel access door, even if only to reset a circuit breaker. But have you ever wondered what’s inside the box? Here’s a guide to the components that make up a modern electrical panel.
Circuit Breakers
Every modern electrical service panel contains circuit breakers. They’re safety devices that protect against two types of dangerous faults. One is overheating. Circuit breakers contain a bimetallic strip that carries incoming voltage. The alloy used has a useful quirk: it bends when heated past a predetermined temperature. That way, if the protected circuit is under heavy use for too long, the strip overheats and trips the circuit breaker. The bimetallic strip is more sensitive than the wiring it protects, so it always overheats before the wiring does.
The second type of fault a circuit breaker protects against is a short circuit. That’s a condition in which electric current takes a lower-resistance path than it’s intended to follow. That results in a surge of current that exceeds a wire’s capacity. It can lead to an electrical fire if not halted immediately. To do this, circuit breakers contain a specially designed electromagnet. It’s only powerful enough to trigger the breaker while experiencing excessive current.
Bus Bars
Electrical panels also contain metal bars, called bus bars, that carry current where needed. In general, electrical panels contain three types of bus bars. One is a hot bar. They’re the ones that carry incoming voltage from your power company to your circuit breakers. Each hot bus bar carries 120 volts. If you have incoming service of 240 volts, your panel will have two hot bus bars. If you have three-phase electrical service, your panel will have three hot bus bars.
Your electrical box also contains at least one neutral bus bar. It carries voltage returning to the panel after passing through your circuits. Then, it travels back into the electrical grid. Occasionally, electrical panels have neutral bus bars that double as grounding bus bars. Or, yours may also have a dedicated ground bus bar. That provides a safe route for stray voltage to reach a rod driven into the soil on your property. That serves as protection against voltage spikes, such as those caused by lightning strikes.
Main Bonding Jumper
A main bonding jumper is a bare, copper wire connecting the panel’s ground bus to the grounding rod. You’ll often see it connected to the ground bus via a green screw terminal. It bonds the panel’s ground bus, rod, and neutral bus. That way, any voltage spike will still trigger the appropriate circuit breaker. The wire itself has higher resistance than the neutral wire, so it’s only energized during a spike.
Now that you know all the main parts of an electrical panel, you can better appreciate the work they do. And while deceptively simple, electrical panels are a critical part of your property’s electrical system. If you live in Savannah, GA or a surrounding area and need an electrical panel upgrade, make your first call to TNT.
