Understanding Your Home's Electrical Load

You don't need to be an electrician to know the capacity of your home's electrical load. Brush up on some basic knowledge about fuse boxes and service panels that will help you use energy safely and efficiently.

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A basic understanding of your home's electrical load is important knowledge for homeowners. After all, there will certainly come a time in your home's life when you'll need to shut off or restore power. We'll walk you through four key tools for working with electrical loads: how to evaluate your home's load, how to add capacity, how to understand the size of your load, and how to inspect a service panel. 

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Evaluate Your Home's Power Load

Different homes need different amp services. A 60-amp service is probably inadequate for a modern home. A 100-amp service is good for a home of less than 3,000 square feet that does not have central air-conditioning or electric heat. A home larger than 2,000 square feet that has central air-conditioning or electric heat probably needs a 200-amp service. Use the equation listed above to deduce exactly how many amps your home needs. 

Add Capacity to Your Load

Installing a new circuit is not difficult, but before you begin, make sure your service panel can handle the extra load. A service panel with too many circuits is dangerous.

Fuse boxes rarely have space for new circuits. If you have a fuse box and need new service, replace the fuse box with a new service panel or install a subpanel.

If you see an available slot in a breaker box, either an open space or a knockout that can be removed, chances are you can simply install a new breaker there and run cable to it. If there is no open space, local codes may allow you to replace a single breaker with a tandem breaker, which supplies power to two circuits.

Make sure you do not overload your service panel. A panel's total amperage is printed near or on the main circuit breaker, which controls all the circuits in the panel. Most breaker boxes are 100, 150, or 200 amps. Add the amperages of all the individual breakers in the box. The total may be more than twice the total amperage of the box. For example a 100-amp service panel may have circuit breakers that add up to more than 200 amps. This is normal.

Take your total amperages and the name of the service panel manufacturer with you to meet with the inspector to ask about adding another circuit. Or compute your home's power needs.

Know the Right Size: Small Fuse Box

It's also important to know the size of your electrical load box. A small, 60-amp fuse box may be found in an older home that has not had its wiring upgraded. It can supply power to only one 240-volt appliance and is probably inadequate for a home of 1,200 square feet or more.

Medium-Size Service Panel

A 100-amp service panel provides enough power for a medium-size home, even if it has several 240-volt appliances and central air-conditioning.

Large-Capacity Service Panel

Many newer homes and some older large homes have a 150- or 200-amp service panel.

How to Inspect a Service Panel

A service panel should be located where adults can get to it easily but children can't. Any exposed cables leading to it should be firmly attached to the wall and clamped tightly to knockout holes in the panel. If there are any open holes, cover them with a knockout plug (available at hardware stores).

If a 14-gauge wire is connected to a 20-amp circuit breaker or fuse, replace the breaker or fuse with one that is 15 amps to prevent the wire from overheating. In most cases, a 20-amp fuse or breaker should connect to a 12-gauge wire; a 30-amp fuse or breaker should connect to a 10-gauge wire.

Wires should run in a fairly orderly way around the perimeter of the panel. If you find a hopeless tangle, call in an electrician for an evaluation. Also call in a pro if you find melted or nicked wire insulation, any signs of fire, or extensive rust.

In an older home there's a good chance that new wiring has been added to a service panel. It may have been done by a pro, but it could be amateur work too, so check all the connections.

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