Can I Derate for Multipl HVAC Units?

[stuartdmc]

I have 5 20ton AC on the roof and I want to feed them all from a 225A 480v 3ph panel. each AC's MCA are 51@ 480V, all AC's are serving the same room that must maintain 60 degrees at all times.

Question, because I have 5 ACs supplying the same room with one thermostat, can I derate so to fit all 5 AC's on the 225A panel?

Thanks for the help.

 

[augie47]

Since all 5 can operate at the same time, what provision would you have to show a reduced load ?
You might be able to use 440.33 to give you a lesser number than 5 X the MCA, but you will need to consider all 5 running at the same time.

 

[GoldDigger]

Since all 5 can operate at the same time, what provision would you have to show a redcued load ?

stuartdmc:
If you can show that even though they may all be called on to operate at the same time there is circuitry which will positively prevent them from starting at the same time you may be in better shape. If not, then even if you meet the standard NEC multiple-motor circuit load calculation without diversity, what happens in practice may be worse than that.
If there is some redundancy among the five units and it is really critical that the room never go over 60 degrees, then feeding all 5 A/Cs through a single panel (with either a local main or a feeder OCPD) is probably a bad design!

Feeding one or two of them from a different panel would avoid your load problems and be a more reliable setup to boot.

 

[eHunter]

stuartdmc:
If you can show that even though they may all be called on to operate at the same time there is circuitry which will positively prevent them from starting at the same time you may be in better shape. If not, then even if you meet the standard NEC multiple-motor circuit load calculation without diversity, what happens in practice may be worse than that.
If there is some redundancy among the five units and it is really critical that the room never go over 60 degrees, then feeding all 5 A/Cs through a single panel (with either a local main or a feeder OCPD) is probably a bad design!

Feeding one or two of them from a different panel would avoid your load problems and be a more reliable setup to boot.

:thumbsup:

If it is a truly redundant unit system, feeding at least 2 of the units from a different source would highly be recommended.
That way a feed circuit could be taken out of service for inspection/maintenance/repair without taking down all of the AC units and hopefully maintain the 60 degree temp and uptime.

 

[stuartdmc]

stuartdmc:
If you can show that even though they may all be called on to operate at the same time there is circuitry which will positively prevent them from starting at the same time you may be in better shape. If not, then even if you meet the standard NEC multiple-motor circuit load calculation without diversity, what happens in practice may be worse than that.
If there is some redundancy among the five units and it is really critical that the room never go over 60 degrees, then feeding all 5 A/Cs through a single panel (with either a local main or a feeder OCPD) is probably a bad design!

Feeding one or two of them from a different panel would avoid your load problems and be a more reliable setup to boot.

Boot shoot boogy man,That's It!

That's what I'll do.
It would be cheaper to feed one or two AC Units from another panel then to enlarging the existing 225A panel to a 300/400A.

Thanks GoldDigger.

Got to love this forum and the people on it!