Power Output And Demand - Westinghouse iGen Series User Manual

OPERATION

POWER OUTPUT AND DEMAND

120 Volt AC devices have two different electric power demands that must be taken into
consideration, namely the running power and the starting/peak power. Both are measured in
Watts (typically abbreviated as "W").
The steady state continuous load is the running power demand and this is often marked
on the device near its model number or serial number. Sometimes the device might only
be marked with its voltage (i.e. 120 V) and current draw (e.g. 6 Amp or 6 A), in which case
the running power demand in Watts can be obtained by multiplying the voltage times the
current, e.g. 120 V × 6 A = 720 W.
Simple resistive 120-Volt AC devices such as incandescent bulbs, toasters, heaters, etc.
have no extra power demand when starting, and so their starting power demands are the
same as their running power demands.
More complex 120-Volt AC devices containing inductive or capacitive elements such as
electric motors have a momentary extra power demand when starting, which can be up
to seven times the running power demand or more. Manufacturers of such devices rarely
publish this starting power demand and so it's often necessary to estimate it. A rule of
thumb for devices fitted with an electric motor is to apply a starting power multiplier of 1.2
for small hand-held or portable devices and a value of 3.5 for larger stationary devices.
For example, a 900 W angle grinder can be assumed to have a starting power demand of
at least 1.2 × 900 W, which equals 1,080 W. Similarly, a 1,650 W air compressor can be
assumed to have a starting power demand of at least 3.5 × 1,650 W, which equals 5,775 W.
To prevent overloading of the generator's 120-Volt AC system:
1. Add up the running power demand of all the 120-Volt AC devices that will be connected
to the generator at one time. This total must not be greater than the generator's
specified running power output.
2. Add up the running power demand again, but for the largest motor-driven device use
the value of its starting power demand instead of its running power demand. This total
must not be greater than the generator's specified starting power output.
3. The total running power demand of all the devices that will be connected to any one of
the generator's outlets must not exceed the generator's specified running power output.
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