Circuit Breakers 101

LESLIE: Well, we’ve all been there: you’re in the middle of something when – poof – the lights go out. It seems to happen at the worst possible time, too.

TOM: Well, it might be a nuisance but circuit breakers trip for a major safety reason. Here to tell us why and how circuit breakers actually work is Scott Caron, the master electrician for TV’s This Old House.

Welcome, Scott.

SCOTT: Hey. It’s good to be here.

TOM: So, let’s talk about, first, what exactly circuit breakers are and how they work to protect you from fires.

SCOTT: Sure. So a circuit breaker does two things. First and foremost, it protects wires. And then there’s two types: there’s an overload and there’s a short circuit. Now, when that circuit breaker gets overloaded either from too many appliances or too many things on at the same time, it’ll shut off. In a short-circuit situation, if those wires touch or something happens that’s drastic, it also shuts off really quickly.

LESLIE: So with circuit breakers, I mean they’re really only supposed to provide a certain amount of power. And if they’re drawing too much and the circuit overheats, they’ll trip, right?

SCOTT: Yes. That wire is matched to that circuit breaker and vice versa. So on a 15-amp circuit breaker, that wire is rated for 15 amps. Same thing with 20 and 30.

TOM: So how does that differ from a fuse?

SCOTT: Believe it or not, fuses are safe. Once they shut off, they’re off until you unscrew the fuse and put a new one in. They’re not as convenient, which is why we came from fuses to circuit breakers.

TOM: Now, there are new types of circuit breakers out there right now. And one of the most recent is a type of circuit breaker called an “arc-fault circuit interrupter.” How do they work?

SCOTT: So an arc-fault circuit interrupter or an AFCI, it works by sensing any sort of power spark. So if the positive and the negative touch, then it shuts right off immediately. And these are all required from code as you build a new house today. You need to put one in. If you add a circuit to a room, you need to use this particular circuit breaker. And they just came out with an arc-fault circuit outlet.

TOM: So how does that work? How is that different? Does that actually protect everything that’s on the same circuit by having one AFCI? Does it control the entire circuit?

SCOTT: So the arc-fault outlet, which is really nice – if you’re adding an outlet from another outlet, you can swap out the regular outlet and you’ll have arc-fault protection from there on afterwards. It’s a nice way of doing an additional outlet off of another situation that you can’t get to the main electrical panel. That’s the basics of it.

TOM: So basic, it’s sequential. As long as it’s at sort of the start of the circuit, it will protect everything that follows?

SCOTT: Yes. That’s right.

TOM: Now, these sound very similar to what a ground-fault does. How would you describe the difference between a ground-fault circuit interrupter and an arc-fault circuit interrupter? The ground-fault is one that we’re used to seeing in damp locations, right?

SCOTT: That’s right. So they both interrupt the power going to the end device, whatever that might be, whether it’s an outlet or a light fixture. The ground-fault, it does exactly what it says: it senses a very small amount of electricity travelling to ground – milliamps, a really tiny amount – and it shuts it off immediately. So, therefore, somebody can’t get electrocuted. They use them in all wet environments, like your kitchens, your bathrooms and outdoors.

TOM: So what about code considerations? Are these new types of circuit breakers actually required in buildings yet?

SCOTT: So, yeah. In new homes today, we’re using arc-fault circuit-interrupter breakers on almost every single circuit in the house. And the ground-faults – again, if there’s water outside, inside, garage, we’re using those, as well.

TOM: Great upgrades, great information. Scott Caron, the electrical contractor on TV’s This Old House, thank you so much for stopping by The Money Pit.

SCOTT: You got it. It was fun to be here.

TOM: And This Old House is brought to you on PBS by Lumber Liquidators. Hardwood floors for less.