| Determining Your Stand-By Power Requirements |
Make a list of the appliances and motors that must run during an electrical power failure. It is
suggested for stand-by service that you include only essential equipment.
When you have completed the list,
enter the number of watts required to operate each item. The watts required for operation are usually stamped
on the nameplate of the product (note: if only the ampere rating appears on the product, multiply the amps by the
voltage to obtain the wattage). Also, 1000 watts equals 1 KW.
Remember that electric motors require more
power when starting than when running. Starting one motor at a time, beginning with the largest down to the
smallest, will reduce the size of the alternator you need.
Some motors require more starting current
than others, and all require more starting current than running current. Split-phase motors are more difficult
to start and require 5 to 10 times as much current compared to running current, dependent on the NEMA code
letter rating. Motors with capacitor start require 2 to 4 times as much current to start compared to running current.
Determine your largest motor starting requirement by the HP rating and the NEMA code letter on the nameplate.
Refer to the table below for the approximate wattage per HP by NEMA code letter. For the total starting wattage required,
multiply this figure by the HP size of your motor.
Total all requirements, and add approximately 25%
for overlooked items and miscalculations. Select an alternator that is equal to or greater than the rated output
requirement of your load. Never pick an alternator smaller than your load requirement, as damage can be done to the alternator
by continuously overloading it. |
|
NEMA Code Letter |
Wattage Per HP |
|
A |
3100 |
|
B |
3500 |
|
C |
4000 |
|
D |
4500 |
|
E |
5000 |
|
F |
5600 |
|
G |
6300 |
|
H |
7100 |
|
J |
8000 |
|
K |
9000 |
|
L |
10,000 |
|
M |
11,200 |
|
N |
12,500 |
|
P |
14,000 |
|
R |
16,000 |
|
S |
18,000 |
|
T |
20,000 |
|
U |
22,400 |
|
V |
26,000 AND UP |
|
|
|
Approximate Starting Wattages |
|
Motor |
Approx. Running Wattage All Motors |
Split Phase Motors |
Repulsion Induction Motors |
Capacitor Start Motors |
|
HP |
Full Load |
Average Load |
Full Load |
Average Load |
Full Load |
Average Load |
Full Load |
Average Load |
| 1/6
|
528
|
343
|
5,280
|
3,432
|
1,320
|
858
|
2,112
|
1,373
|
| 1/4
|
696
|
453
|
6,960
|
4,524
|
1,740
|
1,131
|
2,784
|
1,810
|
| 1/3
|
864
|
562
|
8,640
|
5,616
|
2,160
|
1,404
|
3,456
|
2,246
|
| 1/2
|
1,176
|
765
|
11,760
|
7,644
|
2,940
|
1,911
|
4,704
|
3,058
|
| 3/4
|
1,656
|
1,076
|
|
|
4,140
|
2,691
|
6,624
|
4,306
|
| 1
|
1,920
|
1,248
|
|
|
4,800
|
3,120
|
7,680
|
4,992
|
| 1-1/2
|
2,400
|
1,560
|
|
|
6,000
|
3,900
|
9,600
|
6,240
|
| 2
|
2,880
|
1,872
|
|
|
7,200
|
4,680
|
11,520
|
7,488
|
| 3
|
4,080
|
2,652
|
|
|
10,200
|
6,630
|
16,320
|
10,608
|
| 5
|
6,720
|
4,368
|
|
|
16,800
|
10,920
|
26,880
|
17,472
|
| 7-1/2
|
9,600
|
6,240
|
|
|
24,000
|
15,600
|
38,400
|
24,960
|
| 10
|
12,000
|
7,800
|
|
|
30,000
|
19,500
|
48,000
|
31,200
|
|
|
Appliance |
Run Wattage |
Start Wattage |
| Emergency
Requirements Basic Home: |
|
|
| Refrigerator
|
700
|
2800
|
| Chest
Freezer |
500
|
2500
|
| Lights
10 at 75 Watts |
750
|
750
|
| Microwave
|
1500
|
1500
|
| Television
|
800
|
800
|
| Gas
Furnace Fan 1/2 hp |
500
|
1250
|
| Total
Basic watts (KW=1000 watts) |
4750
|
9600
|
| Other
Additions: |
|
|
| Coffee
Maker |
1100
|
1100
|
| Dishwasher
|
1500
|
3750
|
| Air
Conditioner
|
|
|
| 12000
BTU |
2800
|
7000
|
| 24000
BTU |
4200
|
10500
|
| 32000
BTU |
5000
|
12500
|
| Drill
Motor, sm. |
500
|
500
|
| Freezer
|
500
|
2500
|
| Frying
Pan, lg. |
500
|
500
|
| Frying
Pan, sm. |
150
|
150
|
| Laundry
Dryer Gas |
500
|
1000
|
| Laundry
Dryer Electric |
5500
|
6000
|
| Hair
Dryer |
1500
|
1500
|
| Heat
Pump or Electric Heat |
10000
|
10000
|
| Light
Bulbs |
40
|
40
|
| Light
Bulbs |
60
|
60
|
| Light
Bulbs |
100
|
100
|
| Light
Bulbs |
150
|
150
|
| Motors
1/2 hp |
500
|
1250
|
| Motors
1 hp |
1000
|
2500
|
| Motors
2 hp |
2000
|
5000
|
| Oven
- Electric |
6500
|
6500
|
| Radio
|
100
|
100
|
| Refrigerator
|
700
|
2800
|
| Space
Heater |
1500
|
1500
|
| Stereo
|
120
|
120
|
| Stove
Electric - Per Element |
1500
|
1500
|
| Sump
Pump 1/2 hp |
500
|
1250
|
| Toaster
|
200
|
200
|
| TV,
large |
800
|
800
|
| TV,
small |
100
|
100
|
| Vacuum
Cleaner |
250
|
250
|
| VCR
|
150
|
150
|
| Water
Heater - Electric |
4500
|
4500
|
| Well
Pump 1 hp |
1000
|
2500
|
| Well
Pump 2 hp |
2000
|
5000
|
| Well
Pump 3 hp |
3000
|
7500
|
| Window
Fan |
250
|
250
|
|
|
|
