I am calculating some HVAC loads to install a new panel, and fiquere additional load to existing service. What I have is (22) 5-ton cooling only units. 460V, 3-phase, MCA 13.2A, MOCP 20A, FLA 13A, LRA 71A. Do I fiquere MCA x 22 units x 125% for my load demand? and then size my panel according to that calculation? Thanks.
Load Calculation
- Thread starter DAWGS
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
DAWGS said:
I am by no means one to trust on calculation but it has always been my understanding that for multiple motors you would figure the sum of all the units plus 25% of the largest unit. 440.33
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
spsnyder said:
If you use FLA that already has the 125% built in. If you did that for every unit then it would be the same as dawgs initially stated. Is that correct?
Harold-eng
Member
- Location
- Tampa, FL
You only have to count the largest motor one time. For a single unit, the 13.2 MCA has that one motor built in. For example, if the evap fan was 1.5A, the condensor fan was 0.7A and the compressor was 8.8A, the sum of 1.5+.7+(1.25X8.8)=13.2A
If you sum all the MCAs, you are counting the largest motor 22 times. It would benifit you to find out he running load of each of the components and sum them up, then take 25% of the largest motor one time.
Sum of 22 X (1.5 + 0.7 + 8.8) + (0.25 * 8.8) = 244.2A
VS.
22 * 13.2 = 290.4A
If you sum all the MCAs, you are counting the largest motor 22 times. It would benifit you to find out he running load of each of the components and sum them up, then take 25% of the largest motor one time.
Sum of 22 X (1.5 + 0.7 + 8.8) + (0.25 * 8.8) = 244.2A
VS.
22 * 13.2 = 290.4A
gulkhan123
Member
Harold-eng said:
Harold,
You are right, but if someone has only MCA or FLA data and doesnot have detail data of each part(fan, evaporator, compressor), then how should we calaculate the load? I mean using the MCA or FLA, How to proceed?
gk
Ragin Cajun
Senior Member
- Location
- Upstate S.C.
This thread is helpful in a service sizing issue we have now.
Project is a church served at 480V. There is 330KVA of HVAC - heat pumps and strip heat, no gas available. These are all supplied from a single 480V panelboard and service disconnect. The 120/208V loads are supplied from a separate 150KVA transformer and service disconnect.
Based on this thread, for the HVAC portion of the service we need to use 330 KVA or 396A plus 25% of the largest individual load which is a 20 KW duct heater. The largest compressor is only 13.2A.
Thus, based on the above the ampacity of the conductors would be 402A.
Thus a 450A fuse and 2-4/0 per phase conductors would meet NEC??
Comments?
RC
Project is a church served at 480V. There is 330KVA of HVAC - heat pumps and strip heat, no gas available. These are all supplied from a single 480V panelboard and service disconnect. The 120/208V loads are supplied from a separate 150KVA transformer and service disconnect.
Based on this thread, for the HVAC portion of the service we need to use 330 KVA or 396A plus 25% of the largest individual load which is a 20 KW duct heater. The largest compressor is only 13.2A.
Thus, based on the above the ampacity of the conductors would be 402A.
Thus a 450A fuse and 2-4/0 per phase conductors would meet NEC??
Comments?
RC
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