Two chillers from a single feeder

Junior_EE

Member
Location
New York City
As you can see from the image, I am attempting to power two new chillers from a single feeder. The service switchboard MCB is 3000Amps at 480Volts, 3-phase. I want to feed the chillers from one circuit breaker for two reasons: 1. The distance between the 1600A circuit breaker and the chillers is considerable, and I would only like to run 1200Amps of copper instead of 1200Amps two times, and 2. I do not think I can fit more than a single new 1600A circuit breaker into the existing 3000A service switchboard.

The chillers will not run at the same time. BMS programming will ensure this.

I have a couple of questions:

1.) This design looks strange, so I am wondering if anyone has done something like this before and has run into any issues, especially code-related issues?

2.) Each chiller's cutsheet says that the chiller requires a 1600A max OCPD and 1200A MCA. Would the local disconnect switches need to be 1600A or 1200A?
 

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augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If the two chillers are interlocked so they can not run simultaneously, a single feeder would be allowed. The disconnect would need to be rated per 440.12 at 115% so, IMO, the 1600 amp disconnect would be required.

I would caution to assure there is no "static load" such as condenser heaters, etc. present on the 2nd chiller when not operating
 
Last edited:

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
If the two chillers are interlocked so they can not run simultaneously, a single feeder would be allowed. The disconnect would need to be rated per 440.12 at 115% so, IMO, the 1600 amp disconnect would be required.
The MCA is not the actual current though. The sizing of the switch is based on actual current.
 
I'm not sure that BMS programming would count as a sufficient interlock between machines (would it?). In something like this, where a breaker trip if both machines try to run at once would be a Bad Thing, some local hardware interlocking may be in order; could be as simple as cross-wiring whatever the VFDs call RUNNING and RUN-INHIBIT (so that when one machine starts, the other is blocked from operating).
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I will gladly vow to your knowledge on the subject. My assumption was that chillers had hermetic compressors so I assumed 440 was applicable.
OP didn't give branch circuit selection circuit so I used MCA. My bad !
 

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
I agree with @zbang

In that situation I think you need something more than the BMS interlocking/locking out 1 chiller. Chillers usually need their control circuits and the 3 phase live to be able to run when needed.

They usually have pump interlock circuits that could be wired through a double throw switch or something
 
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