We all know what to do when a fuse blows or a circuit breaker trips: Turn some things off, unplug a few things, then put in a new fuse or reset the circuit breaker. But you’re not doing yourself any favors if everything you disconnected ends up back on the same circuit a few days later.
A blown fuse or tripped breaker is a warning: Something you’re doing with your electrical system is wrong. You need to correct it.
A circuit is all of the electrical outlets or fixtures connected to one fuse or circuit breaker. Usually, a circuit will supply power to one or two rooms or to one or two major appliances.
Home circuits for your lights, television and other small appliances are 120-volt circuits. Circuits for large appliances such as clothes dryers generally carry twice as much power at 240 volts.
Each circuit in your house is rated to carry a certain number of amps, short for amperes or amperage, a measure of the current flow used by an electrical device. Each fuse in your fuse box and each circuit breaker switch is marked with a number indicating the number of amps allowed on the circuit it controls.
Most devices have an amp rating printed on them, usually somewhere in the back where the power cord is attached. Small motors — such as can openers, fans, vacuum cleaners — usually pull about one to three amps. Things that heat up — water heaters, ranges, hot plates, heaters — tend to draw in the 10- to 40-amp range.
Watts, like amps, indicate current flow. The number of watts a device uses is equal to the voltage of the circuit multiplied by the amps of the device. In other words, a three-amp motor on a 120-volt circuit uses 360 watts of power.
To keep circuits from being overloaded, you have to make sure that the total number of amps demanded by the things plugged into the circuit doesn’t exceed the maximum number printed on the fuse or circuit breaker.
An overloaded circuit generates heat, and that makes it a fire hazard.
The first step to managing circuit loads is know which circuit controls every electric outlet, every ceiling light and every other electric device in your house.
If you look inside the service panel, the box that holds the fuses or circuit breakers, you’ll find a circuit list. But in many cases the list is vague and incomplete.
If you haven’t done so before, do a complete survey of each room in your house to check which outlets are on each circuit and make a circuit map.
To do this, one person carries a floor plan with the outlets and switches marked for each room. A second person stands at the service panel to remove fuses or turn circuit breakers off. Mark each outlet location on the plan with the number of the fuse or circuit breaker that controls its circuit.
Keep one copy of the circuit map near the service panel and another with your appliance warranties and other important papers.
Use the map to plan the arrangement of electrical devices around your house. For example, don’t try to use a 10-amp portable heater and a 7-amp trash compactor on the same 15-amp circuit at the same time.
You should also be aware of which outlets in your house are grounded, and which are not. Modern homes have electric outlets with three holes; in grounded circuits, the third prong on an appliance cord goes into the third hole on the outlet and hooks up with a path for electricity to be sent safely into the ground in case of a break in the normal electrical flow. The ground wire reduces the chance of dangerous electrical shock.
If you buy an appliance with a three-prong plug, you can get it to work in a two-prong outlet by attaching an adapter, but utility-company officials say that could be dangerous because you’re defeating the shock protection.
Also, not every receptacle with three prongs is truly grounded. You can buy inexpensive circuit testers at home-improvement stores to test the grounding of your outlets.
If you have a device, such as a computer, that needs a grounded outlet, a qualified electrician can add one where it’s required.
According to the U.S. Consumer Product Safety Commission, problems in home wiring, such as arcing and sparking, are associated with more than 40,000 home fires each year. These fires annually claim more than 350 lives and injure 1,400.
A new electrical safety device for homes, called an arc fault circuit interrupter or AFCI, reduces the risk of arcing and will be required in the bedrooms of newly constructed homes in 2002.
The safety commission says typical household fuses and circuit breakers don’t respond to early arcing and sparking conditions in home wiring. By the time a fuse or circuit breaker opens a circuit to cut power to an arcing wire, a fire might already have begun.
AFCIs are different from ground fault circuit interrupters. Ground fault interrupters are installed as power outlets particularly near water sources, and they protect people from electrical shocks. AFCIs are installed in service panels to prevent fires.
