- 1). Calculate the maximum load. Make your first calculation by adding up the total of the amps listed on each breaker in the box. This number will give you the maximum load that is available to all of the electrical circuits in your home. It is not a real indicator of the true load of the box. It will allow you to check whether you have a reasonable load on each circuit as you compute the probable load of the board. Because appliances are plugged and unplugged from the electrical supply of the house, the actual load varies from time to time.
- 2). Make a list of every fixture and appliance that regularly uses electricity in your home. Items like the refrigerator, microwave oven, washer, clothes dryer and dishwasher should be included on the list. Record the appliance, the circuit that it is attached to and the electrical load that it requires. Most appliances have the number of amps that they require on a plate attached to them. To calculate the needed amp from lights, divide the watts used by the volts. For example, a 60 watt bulb on a 120 volt circuit will use 1/2 amp. On items with moving parts that start and stop, add about 10 percent extra for the increase in power requirements at start up.
- 3). Calculate total circuit board load. Add up the total amps required by circuit. This will give you the amp load per circuit. Add the load of all of the circuits together to arrive at the load of the total circuit board. Realistically, this load will rarely if ever be achieved because not all appliances and fixtures operate at the same time in most homes. However, this may give you some insight into why breakers open when one appliance is on and another one is started.
- 4). Complete the process by adding in the occasional use items that require electricity. Vacuum cleaners, hair dryers, electric razors and other such devices add into the load of the circuit board when they are in use. The same is true for small kitchen appliances.
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