Design Topics
February 2003
Sizing an Electrical Service
Prospective tenants and buyers of manufacturing facilities need to know if the building or suite they are considering has an Electrical Service sized for their needs. A property marketing flyer will generally list the service size; which is commonly expressed in amps/volts i.e. 600 amps at 480 volts. Use the tables below to calculate the building load as well as any equipment load and to verify the adequacy of the existing service. Its easy as A,B,C, and D.
Tables A and B (items 1 through 6) deal with power requirements by square foot, Table C, Items 7 through14 take into account specific loads (client furnished data) and Table D completes the calculation by converting watts back into amps based on the the available voltage.
TABLE A
|
No.
|
Power required for lighting by square foot |
Enter s.f. |
X |
Watts per s.f.
|
= |
Total watts
|
| 1 |
Office or assembly area lighting |
|
x |
1.3 |
= |
|
| 2 |
Industrial Hi-Bay lighting |
|
x |
1.2 |
= |
|
| 3 |
Industrial Low-Bay lighting |
|
x |
1.0 |
= |
|
| 4 |
Industrial precision task lighting |
|
x |
1.5 |
= |
|
| 5 |
Storage or warehouse lighting |
|
x |
0.6 |
= |
|
|
TABLE B
|
No.
|
Power required to run air conditioning |
Enter s.f. |
X |
Watts per s.f.
|
= |
Total watts
|
|
6
|
Enter area to be heated and cooled |
|
X |
1.3
|
=
|
|
|
TABLE C
| No. |
Power required for specific loads |
Count each |
X |
Watts each |
= |
Total watts |
| 7 |
General purpose 110v outlets |
|
X |
180 |
= |
|
| 8 |
Dedicated 20 amp 110v outlets |
|
X |
1,200 |
= |
|
| 9 |
20 amp - 208 v, single phase |
|
X |
3,328 |
= |
|
| 10 |
30 amp - 208 v, single phase |
|
X |
4,992 |
= |
|
|
11
|
50 amp - 208 v, single phase |
|
X |
8,320
|
=
|
|
|
12
|
20 amp - 208 v, three phase |
|
X |
5,757
|
=
|
|
|
13
|
30 amp - 208 v, three phase |
|
X |
8,636
|
=
|
|
|
14
|
50 amp - 208 v, three phase |
|
X |
14,393
|
=
|
|
|
| Enter total number of watts entered on tables A,B,C |
|
|
The last step- You must know the the voltage of the existing service, which you've gotten from the marketing flyer, the meter section in the electical room or the transformer feeding the subpanel to which loads entered in the above tables will be connected. Knowing the voltage, take the total of watts and insert it into one of the two lines below.
Select I. or II. below |
Enter Watts Total |
Divide by |
Divide result by |
= Total Amps Required |
I. |
For a 480 volt service |
|
480 |
1.73 |
X |
II. |
For a 208 volt service |
|
208 |
1.73 |
X |
|
The electrical service required is X number of amps at the voltage (lines I. or II.) in which you entered your total watts.
NOTE: In cases I. and II. the service ( 408volt or 208 volt) is presumed to be 3 phase. In rare cases the service will be single phase, in which case the calculation skips the step of dividing by 1.73 and consequently the "amps required" result is significantly increased.
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