Subpanels—a Real Convenience

Subpanels are smaller versions of your main service panel. They serve a couple of purposes:

• They provide proximity to circuit breakers, especially in large homes, so you don’t have to access the main panel some distance away.
• They can expedite the wiring of a large house because the electrician only has to run one feeder cable from the main panel to the subpanel instead of running cable for every circuit separately the same distance. A subpanel on the second floor of a large three-story house, for example, enables you to control the circuits on the second and third floors. Like your main panel, you have to follow a few rules regarding the location of a subpanel:
• It cannot be installed in a bathroom.
• It cannot be installed in a closet.
• The subpanel must be in an accessible, visible location.

Breaker, Breaker

Circuit breakers, along with fuses, are known as overcurrent protective devices. They protect you, your electrical equipment, and your wiring. They are matched to the ampacity of a circuit’s conductors, and they shut the current down if there’s an overload or a short-circuit. Breakers are clearly marked (15, 20, 30 amp, and so on) and must be used accordingly. You can’t stuff a 20-amp breaker into your panel box and use it on a 15-amp circuit, especially if the circuit only has 14-gauge wire. This is a recipe for fire because you’ll be allowing the wire to carry more current than it’s designed to carry, and the breaker won’t sense the problem and thus won’t trip.
Breakers are either single pole or double pole (sometimes referred to as a two-pole breaker). Double-pole breakers are used for 240-volt circuits and draw power from each of the 120-volt hot wires entering the panel. A double-pole breaker can be either a single device or two single-pole breakers tied together so they’ll both shut off at the same time.

Grounding Your Panel

A big safety advantage in newer service panels over old fuse systems is the fact that they’re grounded. The code is very specific about grounding procedures including
…
➤ The size of the grounding conductor.
➤ What is and is not an acceptable grounding electrode.
➤ Bonding requirements and the use of clamps and bonding bushings.

A service panel is grounded twice when possible: once to your water pipes (assuming they’re metal and not plastic) and once to a grounding rod buried in the ground. When a grounding rod cannot be used due to soil conditions, a length of copper wire can be buried directly in the earth (a minimum of 21/2 feet deep) or encased in concrete at least two inches thick that has direct contact with the ground (usually a foundation).
There also are other means of grounding the system (depending on your soil and house construction). The materials allowed, their installation, and their dimensions are all spelled out extensively in Article 250 of the code. Electricians know this stuff by heart because they use it every day. You, on the other hand, will never use it again, so consider calling an electrician for your panel installation.