Subpanels Explained for Home Owners

The heart of a home's electrical system is the main circuit breaker box, also known as the main service panel. This is where the power feed from the utility company first enters the home from the meter and the point at which all the power is distributed to the various branch circuits of the house. All homes have a main service panel.

A subpanel is a smaller service panel that distributes power to a specific area of the home or other buildings on the property. It is essentially a satellite circuit breaker panel that has its own breakers. It can be placed anywhere inside or outside of the house, as long as it is at least a foot away from the main circuit breaker box.

The subpanel is fed by a double-pole 240-volt breaker at the main service panel, and this single feed circuit is divided into additional branch circuits at the subpanel. A subpanel does not add amps to your home's electrical system because it feeds off current from the main panel, but it does help take the load off of the main circuit breaker. However, you or your electrician will need to calculate how much of a load a subpanel can handle.

Benefits of Subpanels

Subpanels are usually used to extend the wiring for multiple branch circuits to a specific area of a home or a building at some distance away from the main panel. The space that may need a subpanel usually has specific or heavy electric needs. Here are some examples of where putting a subpanel might make sense:

• Garage
• Outbuilding
• Workshop
• Room addition
• Home office
• Home theater

The idea is to run a single set of feeder wires from the main panel to a subpanel, where the power will then be divided into multiple branch circuits serving that building or area of the house. The circuits running from the subpanel may power light circuits, outlet circuits, or appliance circuits—just like the main service panel. Subpanels are added to a system for three common reasons: space, convenience, and efficiency.

Space

When all the breaker slots in the main service panel are full and cannot accept any more circuits, a subpanel can be an ideal way to add additional circuits. By running a single 60-amp breaker to a subpanel, for example, you can then divide those 60-amps into several smaller circuits. 

Convenience

Circuits can be controlled from a more convenient location rather than returning all the way to the main service panel, which might be at some distance. In a garage with a workshop, for example, power tools might occasionally trip circuit breakers, and resetting them is much easier if you can do it from the garage subpanel rather than returning to the main service panel. 

Efficiency

Installing a subpanel can save time and construction costs by reducing the number of "home runs" back to the main panel. It costs more in materials and labor to run three or four individual circuits from a remote location back to the main panel than it does to run a single high-amperage circuit and then divide it into smaller circuits from the subpanel. 

How a Subpanel Is Connected

A subpanel requires two hot wires connected to a 240-volt double-pole breaker in the main panel. It also needs a neutral wire and a ground wire. The cable used for this run is known as a "three-wire cable with ground." The two hot wires, called feeder wires, will provide all of the power to the subpanel. This cable run connects to a 240-volt main breaker or main lugs in the subpanel, which feeds power down through two hot bus bars. Individual circuit breakers will connect to these bus bars to distribute power to the branch circuits running out from the subpanel.

When You Don't Need an Electrical Subpanel

If you are experiencing problems with the electricity in your home, an electrical subpanel may not be the answer. You may need an electrical service upgrade. Here are clues that you need an upgrade rather than a subpanel, but it is always best to consult a licensed electrician to confirm your needs:

• You're resetting your circuit breakers constantly even if you're running a low-power appliance, like a vacuum cleaner.
• Lights dim in your home when you're using an appliance.
• Your electrical panel at the main circuit breaker feels warm to the touch.
• Your outlets feel warm and you may smell a "burning" odor.
• You may be relying heavily on extension cords around your home and they also feel warm to the touch.
• Your electrical panel has not been upgraded for several decades.