- 1). Make a list of each piece of electrical equipment the generator will power, such as appliances, furnaces, lights and computers.
- 2). Measure continuous power rating for the generator or the amount of power consumed by all items running simultaneously. Locate the main disconnect box, and remove the front cover. Wearing gloves, clamp the meter to the line wire. Take separate current readings for each hot---usually black---wire. Add volt-amp readings from each wire together, and multiply by 120 for wattage figure. To ensure power consumption is measured accurately, take several readings approximately 10 minutes apart, and select the highest reading. Add an additional 20 percent safety margin to the total wattage.
- 3). Determine surge current requirements. Many appliances such as refrigerators, furnace fans and air conditioners are driven by motors, which have higher current requirements when initially starting than when running. This factor must be incorporated into the total wattage requirements for the generator. Remove the cover from the distribution box. Set the meter to Peak or surge reading. Wearing gloves, clamp the meter to the wire feeding appliance. Ask an assistant to turn on an appliance; record the surge current reading. Repeat for each appliance to be powered by the generator. Assuming only one appliance will start at a time, determine which item has the greatest difference between running and surge current. Add the difference to the total current for all items.
- 4). Determine if more than one appliance will need to start simultaneously. If so, the generator selected should provide enough starting current for multiple loads to prevent overheating, burning out or tripping the generator's circuit breaker. Refer to earlier surge current readings for appliances. Add the difference between running and surge currents for each selected item to get the total current requirement.
- 5). Make a list of appliances and equipment with solid state circuitry, such as radios, televisions, microwave ovens and computers. These items are highly voltage sensitive and can be damaged by harmonic distortions in electrical power. If they are to be powered by the generator, it should stabilize its output and prevent distortions.
- 6). Select a generator with a continuous rating equal or larger to the total wattage requirement calculated and which can produce a wave-form with less than 10 percent harmonic distortion.