3 Phase loads

Status
Not open for further replies.
H

haremmac

Member
Location
United States
Hi Guys,
Hoping you can help with this calculation:

I have 12 compressors connected to a 200 amp sub panel that is fed from a 3 phase main panel. The 3 phase main panel has a max of 225 amps at 208 volts. The main also has a 50 amp elevator breaker in it. The loads on the 200 amp sub are as follows:

2 compressors at 31.5 FLA
5 compressors at 23 FLA
5 compressors at 26 FLA

All the compressors serve air conditioning equipment.
The elevator is not in service and it will not be for the foreseeable future. I do want to include something in the calculation for this elevator because it will have to be put back into service at some point in the future.

I need help finding the total load in amps for this setup to see if there is any room for any additional loads. Thank you for your help!
 
Are the compressor motors you list all three phase?
If so, you seem to be overloaded without even adding in the elevator if they may all run at the same time. If you can justify a diversity factor you may be OK though.
You certainly do not want them all to try to start at once. :)

Tapatalk!
 
Then even though they are connected to a three phase panel, please do not call them three phase loads.
The line currents you see on the sub panel will depend on the degree to which the line-to-line loads are imbalanced.
Since they will be independently operated, you may have to consider the worst case combination. To do that you need to specify exactly how the 12 loads are connected to the three lines.
The elevator is actually a three phase load or is it single phase too?

Tapatalk!
 
The elevator is a 3 phase load. I don't know the exact amperage of it but its on a 3phase 50 amp breaker. I really appreciate your help golddigger.

Im just looking for an approximate calculation for the load if anyone can post the formula you would use in thisssituation I would greatly appreciate it.
 
If there is a power interruption, do the compressors come on automatically when power is restored, or do they have to be manually started? If automatic, then they might benefit from having a delay built into each one, or at least some of them.
 
haremmac said:
...I need help finding the total load in amps for this setup to see if there is any room for any additional loads. ...
Click to expand...

GoldDigger said:
...you need to specify exactly how the 12 loads are connected to the three lines.
The elevator is actually a three phase load or is it single phase too?
Click to expand...

haremmac said:
The elevator is a 3 phase load. I don't know the exact amperage of it but its on a 3phase 50 amp breaker.

Im just looking for an approximate calculation for the load if anyone can post the formula ....
Click to expand...

If you don't want to follow Golddigger's advice and you just want a guess - but you need a formula so the guess is an accurate, scientific, wild guess, then:
Add up the compressor's VA,
Add in a fudge factor, say, multiply by 1.25
divide by 208, divide by sqrt(3),
Add 80% of the elevator CB -- say 40A.

I'd say the panel is maxed out to overloaded

ice
 
Status
Not open for further replies.
Top