This is a basic guide to selecting a generator. The basic criteria is if the generator has enough power to start up the load, it will have enough power to continually run it.
There are 3 factors to consider when determining the size generator to use on the jobsite.
1) Type of Load
2) Total Watts to be connected
3) Power of the generator
Type of Load
The first factor to consider is the type of load: resistance or induction loads. Electric lights and heating units are examples of resistance loads. Most construction equipment would have induction loads (electric motors).
There are two types of induction load motors. Universal motors which require brushes power hand drills. saws, and concrete vibrators.
Capacitor motors power pumps, air compressors, and table saws, When sizing a generator to these motors, the main difference is that capacitor motors need 1/3 more starting current than universal motors.
The most accurate method to determine wattage is to check the nameplate on the machine. Wattage is figured by multiplying volts times amps.
Load requirements to electric motors differ, but all motors need more power to start than to run. Capacitor motors require up to 6 times more startup power while universal motors draw 1 1/2 to 2 times the running current.
Once you have determined the wattage, you choose your generator. For example, if you want to run 7 100 watt bulbs(700 total watts), a coffee maker(850 watts), a small refrigerator(2000 starting watts), and a 1500 watt radiant heater, you would need a generator with a minimum of 5050 watts.