TP-5592 7/96 Generator Selection and Wattage Requirements A-1
Appendix A. Generator Selection and
Wattage Requirements
General
Consider total wattage requirements (lights, motors,
appliances) when selecting a generator set, or when
sizing wattage usage where available space and
construction limit the size of the generator set.
Motor Loads
When figuring generator set capacity requirements for
loads that include electric motors, do not overlook the
high current demanded by the motors during start-up.
The inrush or starting current is typically 2-3 times
higher than that required when the motor reaches
normal operating speed. Allow reserve for inrush
demands plus other loads which could be on the line as
the electric motor starts. Use Figure 1 as a guide when
selecting generator set capacity requirements involving
motor loads.
Motor
HP
Starting
(inrush)
Watts
Running
Watts
1/4 750 330
1/3 1000 400
1/2 1500 600
3/4 2000 750
1 3300 1100
2 4000 2000
3 5000 3000
Figure 1. Motor Requirements
Lighting Load
The lighting load is usually easiest to calculate. In most
cases, simply add the wattage of each generator
set-operated lamp. Note that not all of the lights or
lampsareonthegeneratorsetACcircuit—someareDC
powered by a 12-volt battery. Make sure the calculated
total wattage includes only lights actually on the
generator set AC circuit.
Air Conditioners
The starting characteristics of air conditioners vary
greatly—one 12,000 Btu unit has, for example, lower
starting requirements than a 10,000 Btu unit of another
variety. When using only one unit, there is usually no
starting problem, provided the lighting and appliance
load is not too high when starting the unit.
Simultaneous starting of two air conditioning units,
however, can present problems if the generator set
capacityis marginal. Becauseofthevariation instarting
characteristics among air conditioners, this publication
makes no statements regarding multiple-motor starting
capabilities of the generator set covered. Consider
delayed starting or use of easy-starting devices on air
conditioner units whenever simultaneously starting
more than one motor.
See Figure 2 for typical air conditioner requirements.
Information will vary with manufacturer.
Air Conditioner Size (Btu/H)
7,000 9,000 12,000 16,000 24,000
Voltage 115 230 115 230 115 230 115 230 230
Full load amps 9.3 4.8 9.9 5.0 11.8 6.3 16.3 8.0 11.6
Rated load amps 7.7 4.0 7.0 3.5 8.9 4.8 13.0 6.2 10.2
Locked rotor amps 34.0 20.0 40.0 20.0 50.0 31.0 75.0 36.0 56.0
Starting (inrush) watts 3910 4600 4600 4600 5750 7130 8630 8280 12,900
Running watts 886 920 805 805 1020 1100 1500 1430 2350
Figure 2. Typical Marine Air Conditioner Requirements (60 Hz)
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