We get a lot of questions on our electric wiring articles from folks tackling electrical projects in their own home. One of the most common and intimidating parts of electrical work is dealing with the main breaker panel.
This article provides an overview of a breaker panel. If you’re tackling an electrical project, we highly recommend a professional resource that can show you all the details of your project, like this home electric wiring book by Stanley that we use all the time.
While electrical work isn’t always complicated, it can be dangerous. Some jurisdictions require you to be an electrician to perform any electrical work, even in your own home. Almost all jurisdictions require you to get a permit to complete any substantial electric work beyond simple tasks like replacing receptacles. Never perform a task that you aren’t qualified to perform, and always take appropriate precautions.
Electric Breaker Panel Volts and Amps
Before we get started on the panel, note that virtually all homes in the United States are wired with 100-200 amps @ 220 volt service. For homes equipped with natural gas, propane, or oil heat, 150 amps @ 220 volts is usually enough to meet electric demands throughout the year.
For homes with an all-electric heat system, 200 amps is the minimum recommended service level. In houses with a heated pool or spa, electric radiant floor heat, etc., 250 amps or more is recommended.
220 Volt Main Breaker & Service Entrance Lines
220 volt service is provided by two service entrance lines, each of which carries 110 volts to ground. The service lines are out of phase with each other, hence how you can get 220 volts of total potential across the two wires.
These two service wires come into the panel along with a ground wire (usually the ground is a bunch of strands that surround the hot wires). The service lines connect to a main breaker that controls the whole house and ensures the whole house doesn’t overdraw current from the transformer.
From the main breaker, each of the two service lines connects to one of the power buses on the back of a breaker panel. In the picture below, you can see the two major service lines coming in from the top of the panel.
Service Entrance Lines and Circuit Breakers
You might think that the left half of the panel is powered by one of the feeds, and the right half by another, but this is incorrect.
Going down vertically on each side of the panel, the service line that power the slot alternates.
Remember, panels are generally numbered with the odd numbers down the left and the even numbers down the right. This means that breakers 1 and 3 are powered by different source lines, while breakers 1 and 5 are powered by the same line.
This is by design, and important. You’ll notice that there are some ‘double-size’ breakers in most panels. These breakers are 220 volts breakers that usually power big appliances (like an electric stove or furnace). Since they sit across both lines, they can provide 220 volts of potential to an appliance.
Don’t confuse the double-size breakers with smaller tandem breakers, which can control more than one circuit but can only provide 110 volts of service because they are only connected to one service entrance line.
Service Entrance Ground Wires
The ground wire(s) that enter the house with the hot service entry lines connect to the ground bus in the panel. In the picture above, the bare aluminum ground wires tie into the ground bus on the upper left.
Also connected to this ground bus are the ground (bare) wire from all circuits going out from the panel (both 110v and 220v), and the neutral wire from 110v runs only. In most cases, house wiring is copper. You can see in the picture a bunch of copper (bare, ground) and white (common, neutral) wires connected to the bus.
220V and 110V Circuit Breakers in an Electric Panel
There are two main types of circuit breakers in an electric panel. Here’s how to wire these two different types of breakers:
220 Volt Circuit Breakers – These breakers usually power electric furnaces, dryers, heat pumps, and water heaters.
220 volt breakers each take up 2 slots in the panel. If you are providing power to an appliance that only uses 220 volts (and not a combination of 220 and 110 volts), then you’ll run 2-wire Romex in the appropriate gauge to that appliance.
The black and white wires will be connected to the top and bottom of the breaker, and the ground wire will be connected to the ground bus. (Note that 2-wire Romex actually has 3 wires, 2 current carrying wires–black and white–and a bare ground wire).
In this configuration, most electricians will wrap the white wire with black electrical tape. This makes it easy to see that this particular white wire is actually hot and should not be treated like a neutral wire.
If an appliance is going to use 220 Volts and 110 Volts, 3-wire Romex is required. Remember, 3-wire Romex actually has 4 wires – a black, red, white, and bare. In this setup, the black and red wires go to the breaker, and the white and bare wires go to the ground bus.
110 Volt Circuit Breakers – These breakers are more common and each takes up one slot in the panel. These always require 2-wire Romex of the appropriate wire gauge for the number of amps that will be run on the circuit. In this configuration, the black wire connects to the breaker, and the white and bare wires connect to the ground bus.
What Gauge Wire is Appropriate?
You should always check the code for your area to answer this question. About.com provides this useful table:
Light Fixtures, Lamps, Lighting Runs 15 Amps 14 Gauge Receptacles, 110-volt Air Conditioners, Sump Pumps, Kitchen Appliances 20 Amps 12 Gauge Electric Clothes Dryers, 220-volt Window Air Conditioners, Built-in Ovens, Electric Water Heaters 30 Amps 10 Gauge Cook Tops 45 Amps 8 Gauge Electric Furnaces, Large Electric Heaters 60 Amps 6 Gauge Electric Furnaces, Large Electric Water Heaters, Sub Panels 80 Amps 4 Gauge Service Panels, Sub Panels 100 Amps 2 Gauge Service Entrance 150 Amps 1/0 Gauge
- How to Run a New Circuit from a Main Breaker Panel.
- Free 2008 National Electric Code (NEC) online.
- Professional Digital Multimeter Review.