There are two basic types of panels found at home centers: Main breaker and main lug.

Main breaker panels have a large breaker that disconnects the power to the hot bus bars. A main breaker panel is connected to a service entrance cable that leads into the house from the electric meter.

A main lug panel needs an external circuit breaker somewhere in the line feeding the panel. This could be a two-pole breaker in another breaker panel, or a circuit breaker in a disconnect box outside the house.

Note the S-shaped piece of metal secured by a green screw. This is called a "bonding strap" and is used to connect (or "bond") the neutral bus to ground (the metal case) only when the panel is being used as a main panel.

BUT WE CAN'T DO THIS... because we are using this panel as a subsidiary panel, or sub-panel. This panel is simply a branch of the main panel, and there is a strict rule about this neutral-and-ground connection.

Because if a neutral wire became disconnected (I've seen it happen), the return path for electric current could be along a ground wire. While that itself may not be a hazard, if that ground wire also became disconnected somewhere, parts of the ground system could be energized. That's not EVER supposed to happen.

The neutral wire is essentially a "low-risk" return path for the electric current in that branch of the system. All of the neutral wires all have the same electrical potential... nothing. At least, no potential compared to ground. There is, of course, 120 volts of potential difference between a neutral wire and any hot wire in the residential system.

If you touched the metal part of a live neutral wire you should not receive a shock. (But don't try it!) By tying the neutral to ground at one point, half of the conductors (in a typical 120 volt circuit) have no dangerous electrical potential. Of course, the hot wires are still dangerous. 

Arrow 2 points to a stamped guide line for flush mounting. In new construction, the panel would be installed with this line flush with the face of the studs, when using ½" thick drywall. The shorter line behind would be used with 5/8" drywall.

But... we couldn't use the normal mounting holes. The plaster/lath and drywall multi-layer surface was so thick, the mounting screws would've just bit into plaster.

So we drilled four new holes farther back, so the screws would hit the wood framing.

• Red and black, which are the hot wires.
• White, which is the neutral wire.
• Bare copper ground wire.

Connecting The Sub-Feed
To The Sub-Panel:

1. The hot wires (red and black) are connected to the hot bus bars.

2. The neutral (white) wire is connected to the large lug on the neutral bus bar.

3. The ground wire (bare copper) is connected to the ground bus.

The following photos show close-up views of these connections.

These connectors need to be pretty tight... but I couldn't find a torque specification anywhere on the panel or in the instructions.

The regular terminal points on the bus bar can accept wires from number 14 up to number 8. Larger wires (i.e. a smaller gauge number) require a larger lug.

Note that you can usually buy a large lug like this, which is installed in two terminal points in the neutral bus bar.

6-3 cable uses a smaller ground wire than the conductors (I think it's number 8), so the ground wire can fit into any of the connection points in the ground bus bar.

This circuit simply supplied power to a 2-gang switch box behind the sub-panel. From this point the circuit will feed a string of outlets and a ceiling fan.

We carefully slit the cable jacket and cut away the plastic.

The screw needs to be fairly tight... about 30 to 50 inch-pounds I believe.

A rectangular knock-out needs to be removed from the cover panel to accommodate each breaker.

Close Up:
Circuit Breaker To Panel
Connection

The Cutler-Hammer circuit breaker uses a spring-loaded clamping mechanism to connect to the hot bus bar.

Arrow 1 points to the connector prongs and the horseshoe-shaped spring.

Arrow 2 points to the hot bus bar. This is a sheet of heavy copper that has been folded over to form a wide tab that is grabbed by the breaker prongs.

Warnings And Cautions:

I strongly recommend anybody who plans on doing their own electrical work to do more research besides just reading these articles. I am not an electrician and I certainly do not know everything about wiring. I could be wrong. The electrical codes in your area may be different than in my area.

While minor electrical changes and repairs may not require a permit, larger projects usually do. Consult your local Building Department (look in the "local government" section of your phone book) before making your own major electrical changes. Local electrical inspectors usually are available during their early morning hours to answer your code questions, normally free of charge. If you've done your homework, you can speak intelligently and learn about lots of valuable rules and regulations.

Read HammerZone's disclaimer.