Horizon213
Member
- Location
- Atlanta, GA
I calculated it by multiplying the MCA for the 15kw heat strips X 8 for the number of units. Then 25% of the largest rated motor, which in this case I used the compressor motor. Is this correct?
I think I would take the full load amps of each unit (6+0.5+3+18 = 27.5) times 8 units, and the add 25% of the largest motor.
27.5 * 8 + 1.5 = 221.5A
(I think the 208/230V listed for the indoor fan is a typo.)
I agree although my math is a bit different:
6 x 1.25 (for largest motor) + 3 + 5 +.5 +18 (heater) = 30.5
30.5 x 8 = 244A ~ 250A service.
Thoughts?
I don't see the need to use the 1.25 except for one (the largest) motor.
I agree although my math is a bit different:
6 x 1.25 (for largest motor) + 3 + 5 +.5 +18 (heater) = 30.5
30.5 x 8 = 244A ~ 250A service.
Thoughts?
I agree with Gus, only need to use the 1.25 once.
I'm not sure how you arrived at your answer, though...6 x 1.25 (for largest motor) + 3 + 5 +.5 +18 (heater) = 34 (not 30.5).
Also, I'm not sure where the "5" is coming from in your calculation.
Thanks guys! I calculated MCA which would include all the motors and heaters 33.5 x 8 x 480 x 1.73 = 222,547 va
Then for the largest motor I calculated using the compressor 6 x 1.25 x 480 x 1.73 = 6228
Add the two together 222,547 + 6228 = 228,775 va
228,775 / 480 x 1.73 = 275 amp.
What do you guys think?
((6+0.5+3+18) * 8) + (6 *0.25) = 221.5A is your load.
((6+0.5+3+18) * 8) + (6 *0.25) = 221.5A is your load.
You don't need to use the MCA of each unit, just the FLA. (27.5*8*480*1.732=182,905VA)
And for the largest motor, you would want to add 25%, you added 125%. (6*0.25*480*1.732=1247VA)
(182,905VA + 1247VA = 184,152 VA = 221.5A @ 480V-3ph)
Thank you very much David. You are sure about this?
What is the extra amperage for in the MCA to get to 33.5 from 27.5?
"what do you guys think ?"
??
david showed what he thought twice and I agreed with him.
I see nothing in service calculations that requires you to use MCA.
If you like 275.5 use it.
Do you need to use that number.. not in our opinion.
but
The Code is minimum required.
Your number is great unless someone is bidding against you and uses the required number and you loose the job.