The electrical service in your house is divided into branch circuits, each of which supplies power to a defined area of your home. It is important to make sure that no branch circuit is carrying too great a load, or you will be constantly resetting breakers or replacing fuses. Some appliances need to have a circuit for themselves. An electric stove or dryer will have its own 240-volt circuit; other heavy-use appliances may require their own 120-volt circuits. More often a circuit supplies a number of outlets using a range of power.
To find out if a circuit is overloaded, add up the total power drawn by the circuit as outlined below. Check the breaker or fuse to see how many amps the circuit can deliver. If your total use exceeds the amperage the circuit can supply, change your usage. The solution may be as simple as plugging an appliance into a different receptacle—or you may have to add another circuit to your electrical system.
Typical circuit plan - A well-planned electrical system will have branch circuits that serve easily defined areas or purposes. Unfortunately, many homes— especially if they have been remodeled by do-it-yourselfers— have circuits that roam all over the house. Note that some appliances, such as the microwave oven, dishwasher, and disposal, need their own circuits. The electric stove needs its own 240-volt circuit. Otherwise, circuits are roughly organized by the rooms they serve and by their anticipated demand.
MEASUREMENTS - To figure your circuit loads, total the watts being used. Check the specification label on each appliance. Also note the wattage of the lightbulbs in fixtures on the circuit. Divide the total by 120 (the number of volts). The resulting number will tell you how many amperes (“amps”) the circuit draws when all appliances and lights are on and whether or not you are placing too great a demand on it. Here are some typical watt and amperage figures for common household appliances.
Mapping Your Circuits
When you look inside the door of your service panel, do you see a detailed description of what each branch circuit controls? If not, make a chart yourself. You’ll be glad you mapped the circuits the next time you have to turn off a circuit for repairs or improvements. Begin by making a map of each floor in the house. Take care to include all receptacles, switches, appliances, and fixtures. Be aware that 240-volt receptacles will have their own circuits. With a large house, you may have to make more than one drawing per floor. Mapping is best done with a helper to flip switches and test outlets while you stay at the box and write down findings. If you must work alone, plug in a radio turned to peak volume to find the general area covered by the circuit. The radio will go silent when you switch off the current. Test outlets to find the extent of the circuit.
I. Test each outlet. Mark each circuit breaker or fuse with a number. Turn on all the appliances and lights on one floor. Plug a lamp into every receptacle and turn on. Turn off one circuit and have your helper write the circuit number next to each outlet that went dead.
2. Make a record. Continue the test with every circuit for every floor. Transfer the findings onto a sheet of paper you will affix to the inside of the circuit box door.
The NEC - Electrical codes are based on the National Electrical Code (NEC), which is published by a nonprofit organization and is upgraded periodically. The NEC takes up a huge book that covers every conceivable electrical situation. It provides the model on which virtually all local codes are based. Some communities simply adopt the code as their own; others modify it. Any time you want to make a change in your electrical service, check the NEC and local codes before you begin.
3. Make a circuit load sheet. To really get a fix on how your house uses electricity, combine the information you have just gathered with the power-use information printed on appliances. Write up a load sheet, as shown. It will help you assess capacity for future additions to your electrical system.
Caution! Handle Your Service Panel with Respect - Take special care when working around a service panel. Remove cover plates only when you absolutely have to and replace them as soon as you can. Keep the door shut whenever you are not inspecting the panel. Lock it, if you think your kids may get at it. Remember that even if you have shut off the main power breaker or switch, there is still power entering the box.