Determining the right size generator
To select an engine-driven generator, you’ll
need to determine the power (kilowatt)
requirements which must be met under
operating conditions.
Undersizing the generator can be avoided
by considering all of the loads that will be
connected to the generator, and by determining the starting requirements (motor
start) of electric motor-operated devices.
tools, or other equipment to be connected to lights, heaters, and small appliances, simply
the generator.
add the nameplate ratings or see Chart 1 for
average wattage requirements. For portable
Check the nameplates to determine wattage.
electric tools and equipment, check the
If wattage is not shown, but amps and volts
nameplate rating or use Chart 2 for average
are given, the following simplified formula
requirements. If watts and/or amps are not
may be used:
given and only the horsepower is shown,
Amps x Volts = Watts
use Chart 3 to determine the starting and
(Ex. 12.5 amps x 120 volts = 1,500 watts)
running watts.
To determine kilowatts (kW), use the
Be sure the generator you select is large
following formula:
enough to handle your present requirements
1,000 Watts = 1 Kilowatt
and anticipated needs.
(Ex. 1,500 Watts/1,000 = 1.5 kW)
To determine the right size generator, add
Charts 1, 2, and 3 shown will help you
up the total watts of all lights, appliances,
in selecting the proper size generator. With
Chart 1: Home applications —
Chart 2: Portable electric tools — approximate wattage requirements
approximate wattage requirements
Equipment
Wattage
Air conditioner, 10,000-Btu
Blanket, electric
Broiler
Clothes dryer, electric
Coffee maker
Dishwasher
Fan, attic
Fan, furnace
Fan, window
Freezer, food
Heater, radiant
Hot plate
Refrigerator/freezer
Sump pump
Toaster
TV, color
Water heater
Water pump
2,000–3,000
150
1,400
5,000–10,000
850
1,500–2,500
375
800–1,200
200
300–500
1,300
1,250
600–2,000
400–3,000
1,100–1,700
100–350
3,000–4,500
1,000–3,000
Equipment
Wattage
Equipment
Wattage
Blower, electric
Compressors
Concrete vibrators, 3⁄4-hp
Concrete vibrators, 1-hp
Concrete vibrators, 2-hp
Concrete vibrators, 3-hp
Drain cleaners
Drills, 1⁄4-in.
Drills, 3⁄8-in.
Drills, 1⁄2-in.
Drills, 1-in.
Grinders, bench
Grinders, portable
Hammers, demolition
Hammers, rotary
Heaters, space
Lights
1⁄2–3
Pump, electric
Routers
Sanders, belt
Sanders, disc
Sanders, orbital
Saws, chain
Saws, circular, 6-in.
Saws, cutoff
Saws, jig
Saws, masonry
Saws, radial arm
Saws, table
Screwdrivers
Shears, metal-cutting
Wrenches, impact, 1⁄2-in.
Wrenches, impact, 3⁄4-in.
Wrenches, impact, 1-in.
1⁄2
Chart 3: Motor starting requirements
Running
Motor (hp) watts
1⁄8
1⁄6
1⁄4
1⁄3
1⁄2
3⁄4
1
275
275
400
450
600
850
1,100
hp
1⁄4–3 hp
840
1,080
1,560
2,400
250
250–600
300–600
350–1,200
1,000
1⁄4–1 hp
1,000–2,500
1,260
1,200
1⁄4–2 hp
check wattage on bulb
hp and up
900–1,100
600–1,500
1,200
250
800–1,500
1,000–2,500
2,500
200–800
2–5 hp
1–5 hp
1–3 hp
550
750
600
720
1,200
Chart 4: Insulated copper wire size
Watts required to start motor
Repulsion
Split
induction Capacitor phase
600
600
850
975
1,300
1,900
2,500
Chart 4 is furnished as a guide for selecting the proper size of insulated copper wire
when extension cables are used. We recommend the use of outdoor-rated (U.L.) cable,
recognized type SJTW-A.
850
850
1,050
1,350
1,800
2,600
3,300
1,200
2,050
2,400
2,700
3,600
—
—
Note:
These are suggested guidelines only, please contact a qualified
electrician or licensed contractor for assistance.
Current
in
amperage
2.5
5.0
7.5
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Load in watts
Maximum allowable cable length
at
at
120
240 #4 #6 #8 #10 #12 #14 #16 #18
volts volts wire wire wire wire wire wire wire wire
300
600 —
600 1,200 —
900 1,800 —
1,200 2,400 —
1,800 3,600 650
2,400 4,800 500
3,000 6,000 400
3,600 7,200 325
4,200 8,400 275
4,800 9,600 250
5,400 10,800 225
6,000 12,000 200
—
—
—
625
400
300
250
200
175
150
—
—
—
—
—
400
265
200
150
125
100
—
—
—
1,000
500
330
250
165
125
100
—
—
—
—
—
600
300
200
150
100
80
—
—
—
—
—
—
375
200
125
100
50
—
—
—
—
—
—
—
250
125
80
50
—
—
—
—
—
—
—
—
150
75
50
35
—
—
—
—
—
—
—
—