Sizing Guide
standby
GENERATORS
Generator Sizing Guide
General Information
Important Notice
This booklet is designed to familiarize estimators and installers with proper sizing guidelines for residential and commercial generators. The information is not comprehensive, nor does
it replace or supercede any material contained in any of the written documents shipped with the equipment. This
booklet should only be used in conjunction with the Owner’s Manual, Installation Manual and other technical documents shipped with each product. Always read all accompanying documentation carefully before attempting to install any generator, transfer switch or related equipment.
How to Use this Booklet
Within this booklet, you will find electrical load information, plus an outline of generator surge capability, fuel pipe sizing, liquid propane tank sizing, and UPS / generator compatibility. The final pages are perforated for easy removal and can be photocopied to create additional Onsite Estimating Sheets for use with individual jobs.
Safety Information
Proper sizing of the generator is crucial to the success of any installation and requires a good working knowledge of electricity and its characteristics, as well as the varying
requirements of the electrical equipment comprising the load. When analyzing the electrical load, consult the manufacturer’s nameplate on each major appliance or piece of equipment
to determine its starting and running requirements in terms of watts, amps and voltage. When choosing the generator output for commercial or industrial applications, select a rating that is approximately 25% higher than the peak load (for example, if the load is about 40 kilowatts, select a 50 kW genset). A higher rated generator will operate comfortably at approximately 80% of its full capacity and will provide a margin of flexibility if the load increases in the future.
For safety reasons, Siemens recommends that the backup power system be installed, serviced and repaired by a Generac Authorized Service Dealer or a competent, qualified electrician or installation technician who is familiar with applicable codes, standards and regulations.
It is essential to comply with all regulations established by the Occupational Safety and Health Administration (OSHA) and strict adherence to all local, state and national codes is mandatory. Before selecting a generator, check for municipal ordinances that may dictate requirements regarding placement of the unit (setback from building
and/or lot line), electrical wiring, gas piping, fuel storage (for liquid propane or diesel tanks), sound and exhaust emissions.
If you have a technical question regarding sizing or installation, contact Siemens Technical Service Center toll free at 800-844-0029 during normal business hours (8 a.m. to 5 p.m. CST).
1
Generator Sizing Guide
Table 1 – Motor Load Reference
AC and Heat Pumps
|
|
Running Load |
|
|
Starting Load |
|
|
||
|
|
Running |
Amps at |
Amps at |
Amps at |
Starting |
LR Amps |
LR Amps |
LR Amps |
Description |
Hp |
kW |
240V 1ø |
208V 3ø |
480V 3ø |
kW |
at 240V 1ø |
at 208V 3ø |
at 480V 3ø |
|
|
|
|
|
|
|
|
|
|
1 Ton (12,000 BTU) |
1 |
1 |
5 |
3 |
1 |
3 |
25 |
17 |
7 |
2 Ton (24,000 BTU) |
2 |
2 |
10 |
7 |
3 |
6 |
50 |
33 |
14 |
|
|
|
|
|
|
|
|
|
|
3 Ton (36,000 BTU) |
3 |
3 |
15 |
10 |
4 |
9 |
75 |
50 |
22 |
4 Ton (48,000 BTU) |
4 |
4 |
20 |
13 |
6 |
12 |
100 |
67 |
29 |
|
|
|
|
|
|
|
|
|
|
5 Ton (60,000 BTU) |
5 |
5 |
25 |
16 |
7 |
15 |
125 |
83 |
36 |
7.5 Ton (85,000 BTU) |
7.5 |
7.5 |
37 |
24 |
11 |
17 |
188 |
125 |
54 |
|
|
|
|
|
|
|
|
|
|
10 Ton (120,000 BTU) |
5 Hp (x2) |
10 |
49 |
33 |
14 |
15 |
125 |
83 |
36 |
10 Ton (120,000 BTU) |
10 Hp |
10 |
49 |
33 |
14 |
20 |
250 |
167 |
72 |
|
|
|
|
|
|
|
|
|
|
15 Ton (180,000 BTU) |
7.5 Hp (x2) |
15 |
74 |
49 |
21 |
17 |
188 |
125 |
54 |
15 Ton (180,000 BTU) |
15 Hp |
15 |
74 |
49 |
21 |
30 |
375 |
250 |
108 |
|
|
|
|
|
|
|
|
|
|
20 Ton (240,000 BTU) |
10 Hp (x2) |
20 |
98 |
65 |
28 |
20 |
250 |
167 |
72 |
20 Ton (240,000 BTU) |
20 Hp |
20 |
n/a |
65 |
28 |
40 |
500 |
333 |
144 |
|
|
|
|
|
|
|
|
|
|
25 Ton (300,000 BTU) |
25 |
25 |
n/a |
82 |
35 |
50 |
625 |
416 |
180 |
30 Ton (360,000 BTU) |
15 Hp (x2) |
30 |
n/a |
98 |
42 |
30 |
375 |
250 |
108 |
|
|
|
|
|
|
|
|
|
|
30 Ton (360,000 BTU) |
30 Hp |
30 |
n/a |
98 |
42 |
60 |
750 |
500 |
217 |
40 Ton (480,000 BTU) |
20 Hp (x2) |
40 |
n/a |
131 |
57 |
40 |
500 |
333 |
144 |
|
|
|
|
|
|
|
|
|
|
40 Ton (480,000 BTU) |
40 Hp |
40 |
n/a |
131 |
57 |
80 |
1000 |
666 |
289 |
50 Ton (480,000 BTU) |
25 Hp (x2) |
50 |
n/a |
163 |
71 |
50 |
625 |
416 |
180 |
|
|
|
|
|
|
|
|
|
|
50 Ton (480,000 BTU) |
50 Hp |
50 |
n/a |
163 |
71 |
100 |
1250 |
833 |
361 |
|
|
|
|
|
|
|
|
|
|
General Residential
|
|
Running Load |
|
|
Starting Load |
|
|
|
|
|
|
|
|
|
|
|
|
Running |
Amps at |
Amps at |
Starting |
LR Amps |
LR Amps |
Description |
Hp |
kW |
120V 1ø |
240V 1ø |
kW |
120V 1ø |
240V 1ø |
|
|
|
|
|
|
|
|
Refrigerator, Sump Pump, |
0.5 |
0.5 |
4.9 |
2.5 |
1.5 |
25 |
13 |
Furnace, Garage Opener |
|
|
|
|
|
|
|
Freezer, Washer, Septic Grinder |
0.75 |
0.75 |
7.4 |
3.7 |
2.3 |
38 |
19 |
|
|
|
|
|
|
|
|
General 1 Hp |
1 |
1 |
9.8 |
4.9 |
3 |
50 |
25 |
Well and Septic Lift Pump |
2 |
2 |
19.6 |
9.8 |
6 |
100 |
50 |
|
|
|
|
|
|
|
|
2
Generator Sizing Guide
Table 2 – Non-Motor Load Reference
General Residential
|
Running Load |
|
|
|
|
|
|
|
|
Amps at |
Amps at |
Description |
kW |
120V 1ø |
240V 1ø |
Electric heat per 1000 ft.2 |
12 |
n/a |
50 |
Heat pump elements per 1000 ft.2 |
7 |
n/a |
29 |
Dryer |
5.5 |
n/a |
23 |
Hot tub |
5 |
n/a |
21 |
|
|
|
|
Range oven |
5 |
n/a |
21 |
Hot water |
4.5 |
n/a |
19 |
|
|
|
|
Stove top per burner |
1.5 |
n/a |
6 |
General receptacles per 1000 ft.2 |
1 |
8.3 |
n/a |
Lighting per 1000 ft.2 |
0.75 |
6.3 |
n/a |
Blow dryer |
1.25 |
10.4 |
n/a |
|
|
|
|
Dishwasher |
1.5 |
12.5 |
n/a |
Microwave |
1 |
8.3 |
n/a |
|
|
|
|
Toasters |
1 |
8.3 |
n/a |
|
|
|
|
3
Generator Sizing Guide
Table 3 – Surge Capability
Siemens Liquid Cooled Generators Operating at <3600 RPM
|
Rated Output |
|
Surge Capability |
|
Surge Capability |
|
|||
|
(Running Amps) |
|
LR Amps at 15% Voltage Dip |
LR Amps at 30% Voltage Dip |
|||||
Size (kW) |
240V 1ø |
208V 3ø |
480V 3ø |
240V 1ø |
208V 3ø |
480V 3ø |
240V 1ø |
208V 3ø |
480V 3ø |
|
|
|
|
|
|
|
|
|
|
25 |
104 |
87 |
38 |
71 |
47 |
26 |
133 |
89 |
52 |
70 |
292 |
243 |
105 |
275 |
183 |
106 |
550 |
366 |
212 |
|
|
|
|
|
|
|
|
|
|
80 |
333 |
278 |
120 |
275 |
183 |
106 |
550 |
366 |
212 |
100 |
417 |
347 |
150 |
371 |
247 |
142 |
738 |
491 |
284 |
|
|
|
|
|
|
|
|
|
|
130 |
542 |
451 |
195 |
546 |
364 |
209 |
1088 |
724 |
419 |
|
|
|
|
|
|
|
|
|
|
Siemens Generators Operating at 3600 RPM
|
Rated Output |
|
Surge Capability |
|
Surge Capability |
|
|||
|
(Running Amps) |
|
LR Amps at 15% Voltage Dip |
LR Amps at 30% Voltage Dip |
|||||
Size (kW) |
240V 1ø |
208V 3ø |
480V 3ø |
240V 1ø |
208V 3ø |
480V 3ø |
240V 1ø |
208V 3ø |
480V 3ø |
7 |
29 |
24 |
11 |
23 |
n/a |
n/a |
46 |
n/a |
n/a |
10 |
42 |
35 |
15 |
31 |
n/a |
n/a |
63 |
n/a |
n/a |
|
|
|
|
|
|
|
|
|
|
13 |
54 |
45 |
20 |
38 |
n/a |
n/a |
75 |
n/a |
n/a |
16 |
67 |
56 |
24 |
46 |
n/a |
n/a |
92 |
n/a |
n/a |
|
|
|
|
|
|
|
|
|
|
20 |
83 |
69 |
30 |
63 |
42 |
24 |
121 |
80 |
47 |
25 |
104 |
87 |
38 |
71 |
47 |
26 |
138 |
92 |
53 |
|
|
|
|
|
|
|
|
|
|
35 |
146 |
121 |
53 |
104 |
69 |
40 |
204 |
136 |
78 |
45 |
188 |
156 |
68 |
146 |
97 |
57 |
292 |
194 |
112 |
|
|
|
|
|
|
|
|
|
|
60 |
250 |
208 |
90 |
179 |
119 |
69 |
354 |
236 |
136 |
70 |
292 |
243 |
105 |
246 |
164 |
95 |
496 |
330 |
190 |
|
|
|
|
|
|
|
|
|
|
100 |
417 |
347 |
150 |
333 |
222 |
128 |
663 |
441 |
255 |
150 |
625 |
520 |
226 |
558 |
372 |
215 |
1121 |
747 |
431 |
|
|
|
|
|
|
|
|
|
|
Note: All kW models listed above are based on nominal LP rating.
4