Disaster Rescue  Australian Emergency Manual (Natural Disaster Organization, 183 p.) 
CHAPTER THIRTEEN  LIGHTING AND POWER EQUIPMENT 

13.0 Numerous brands and types of generators are available commercially but all are basically similar in construction, having a frame or case, and a motor driven alternator to produce 240 volts AC (Alternating Current). The ability of the alternator to deliver current, is dependent on its power output rating in WATTS. This is a power rating which is also often rated in KILOWATTS (kW) ie.
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These are commonly used methods to describe the same thing  the POWER OUTPUT OF THE GENERATOR.
Rescuers must know how to calculate the amount of power that a particular appliance will draw so as not to overload the generator:
(a) Lights and heating appliances are normally rated in WATTS. Therefore, when using lights only, it is a simple matter to add the wattage of the number of lights being used and subtract the figure from the generator capacity, to calculate the power still available.eg.
Assume 3 banks of lights, each drawing 500 watts are being used.TOTAL WATTAGE IS 1500W
If a generator was rated at 2500 watts or 2.5kW, it can be seen that there is still 1000 watts capacity left in the generator.
(b) Appliances using electric motors eg. drills, chain saws, refrigerators, fans etc. often indicate the amount of CURRENT drawn from the generator, not the power. This is usually found on a compliance plate on the appliance and is rated in AMPERES or AMPS.i.e.
POWER (IN WATTS) = VOLTAGE (240V) x CURRENT (AMPS)If an electric chain saw is rated at 5 AMPS, the power it draws from the generator is
POWER (IN WATTS) = 240 VOLTS X 5 AMPS = 1 200 WATTS
(c) It can be seen that this particular chain saw can be run from a 2500 WATT (2.5kW) generator, but not from a 1000 WATT (1.0kW) generator.Rescue teams should calculate the POWER rating of each appliance likely to be used, and clearly mark this figure in WATTS on the appliance to save time and possible overload problems during an emergency.
NOTE: Motor starting current is approximately 5 times the rated full load current of electric motors. When selecting generators for motor starting, this factor should be considered to avoid overloads.