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DETERMINING
ELECTRICAL
LOAD FOR
GENERATOR
You must decide what electrical load your generator can power. Do this before
using generator. Use the following four-step method. It will help you select a load
that is not too large. Make sure total wattage of all electrical loads does not exceed
5000 watts. Electric motors present a special problem when figuring load. Read
Step 3 carefully.
1. Make two lists of items you want powered by generator. List all motors and
motor-powered appliances in one. List all lights, small appliances, etc. in the other.
For standby service to home or building, only include items you must power.
2. Enter running watts of each item except motors. The light bulb or appliance
nameplate lists its wattage. Remember, 1KW = 1000 watts.
Note:
The name-
plate may not list wattage. It may only list volts and amps. The formula for
finding wattage is: Volts x Amps = Watts. For example: An appliance name-
plate states 3 amps at 120 volts. 3 amps x 120 volts = 360 watts.
3. Electric motors present a special problem. They require up to 3-times their
rated wattage to start. Chart 2, below, shows starting watts for different size
motors. For example: an electric motor nameplate states 5 amps at 120 volts. 5
amps x 120 volts = 600 watts running. Multiply this figure by 3. This will
show the starting watts needed. 600 watts x 3 = 1800 watts to start. When
figuring the generator load for motors, you must use the starting watts figure.
Do not use the running watts figure.
Note:
Some motors require nearly the
same wattage to run as to start. These items include saws, drills, hair dryers,
and food mixers. See Chart 1 for typical appliance wattage examples.
4. Add watts and starting watts of all items. This total must not be larger than 5000 watts.
It is a good idea to have up to 25% extra capacity for future needs or extra equipment.
* – Always use starting watts, not running watts, when figuring correct electrical load.
x – Motors of higher horsepower are not generally used.
Approximate Starting Watts*
Motor Approximate Universal Repulsion Split
HP Running Motors Induction Capacitor Phase
Rating Watts (small appliance) Motors Motors Motors
1/8 275 400 600 850 1200
1/4 400 500 850 1050 1700
1/3 450 600 975 1350 1950
1/2 600 750 1300 1800 2600
3/4 850 1000 1900 2600 x
1 1000 1250 2300 3000 x
1 1/2 1600 1750 3200 4200 x
2 2000 2350 3900 x x
Chart 2
Running Starting
Equipment Watts Watts
Light bulb (100W) 100 100
Radio 150 150
Fan 200 600
Television 400 400
Furnace fan
(1/3 hp)
600 1800
Vacuum cleaner 600 750
Sump pump
(1/3 hp)
700 2100
Refrigerator/freezer 800 2400
6" Circular saw 800 1000
Floodlight 1000 1000
Running Starting
Equipment Watts Watts
1/2" Drill 1000 1250
Toaster 1200 1200
Coffee maker 1200 1200
Skillet 1200 1200
14" Chain saw 1200 1500
Water well pump
(1/2 hp) 1000 3000
Hot plate/range
(per burner) 1500 1500
Water heater 5000 5000
Chart 1—Typical Electric Appliance Wattages