Our electric service panel is relatively new. The wiring was updated about ten years ago or so and this box was put in. All but one of the 20 circuits in the box were being used when we got the house. The one that didn’t go anywhere was attached to a wire that was cut out when the basement was looted. It likely went to the outlet that ran the sump in the other corner. Even though all the wires do something, it doesn’t mean that they do something useful. In a common residential home, you’ll find a couple of different amperage’s on circuit breakers. I won’t go into the nitty gritty of what that means or how it works, it’s easy enough to just say that a circuit can carry only so much electricity and your amp limit is a numerical value of how much you can carry. The general rule of thumb is that your lights and outlets are on a 15amp circuit. Your major appliances are on a 20amp circuit. And something like an electric dryer or electric oven is going to be on a double circuit. After that you get into very specialized situations. The basic idea of your service panel is you have a big wire bringing all your electricity into the house. It goes into your main shut off at the top of the box. Below that, it splits into some number of individual “circuits” or paths and snakes through your entire house. Each circuit is on it’s own breaker. A breaker is a switch in your box that’s designed to flip off if the circuit is overloaded. This happens when you try to draw too much power through the circuit or there’s a short somewhere in the line. If you’ve ever had your lights shut off because you were vacuuming, watching tv, and running your computer in the same room, then you’ve probably tripped a breaker. The idea is that this fail safe keeps the wires from overheating and burning your house down. Besides the threat of being electrocuted, it’s fire that is the next biggest danger when it comes to your home electrical system. Wires can get really hot. Think about your electric oven or toast. Those are just hot wires in there. So in your service panel, you have a series of circuits, each one governed by it’s own breaker. The breakers are labeled with the amperage that it will handle. Your lights are probably on 15amp breakers, while your fridge is probably on a 20amp. Your main is likely in an increment of 50 (100amp, 150amp, 200amp, etc). The main is just a really big breaker that functions in the same way as the smaller breakers in your box.
For our project, we reorganized the way our electrical system worked. With the exception of the parts we gutted, most of the wiring we found, we kept. But because we were doing things like bringing in a modern kitchen, we needed to take the basic wiring layout and augment it. For example, code requires a few things: 2 dedicated 20amp circuits to run your counter top appliances, 1 dedicated 20amp circuit just for your fridge, a dedicated 240 for your electric oven. But we wanted to add things like a dishwasher, a fume hood, tons of lighting options, maybe a garbage disposal, and additional circuits to run lots of appliances. In order to do this we remapped our current layout. In some places, we pulled circuits together. By that, I mean we took the lights off of one circuit and put them on another, then took the freed up circuit and ran it elsewhere. In the case of the free slot, we actually pulled wire in the basement through the conduit (the metal pipes the wire runs through), put in a new junction box and line, and brought it into the kitchen. In other cases, our changes weren’t so deliberate. There were lines that ran between floors that for one reason or another needed to be moved. It’s really tough to tell what you’re cutting when you don’t know the beginning or the end of the wire. And when there are there of them, it’s easy to make them work again, but when you do, your electric box suddenly doesn’t match it’s labeling anymore. As the final run down when testing the electric system, I turned everything on, remapped all the circuits, and relabeled the box for our new electrical usage. I’m not sure I could completely replace a box on my own, but as part of this project I’ve pulled wire, replaced breakers, and designed new circuit runs so I feel pretty good about my skill level. Several professionals have commented on how nice everything looks. I like that even though a lot of these things are hidden away behind walls, inspectors and trades people care about how tidy and uniform the job is.