Standby chiller

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farmlife

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Hi everyone I just joined this forum. Appreciate any help on this question.

I have a customer who has a 208-230/3/60 30ton air cooled chiller
fed from one 200amp nonfused disconnect.
This disconnect line is protected by a 175 amp breaker.
My question is; can I install and feed a identical standby Chiller
from the same 200amp disconnect? Of course I would install double barrel lugs
on the load side of disconnect to feed both chillers. Each chiller has its own
built in disconnect means.

the main line from 175amp breaker is 2/0 thhn, the line to the
chiller is also 2/0 thhn.

Only one chiller will be turned on at any given moment.
Chiller will be permanently labeled “only use one chiller at a time.
The 200amp disconnect next to the chiller will be labeled MAIN cause
each chiller has its own factory mounted disconnect. Personnel will be trained
limited to operation of chillers.

Does this look doable? I can’t find any code that states otherwise. I did notice
some area in the 400 series code section where there was some suggestion that if
personnel is trained there could be some exceptions.


Gen info:
30 ton 208-230/3/60
rec over current 150 amp. MCA:125amp MOCP: 175amp.

Appreciate any info or guidance.
 
IMO you need a mechanical means to keep both units from operating at the same time like a manual transfer switch. A sign won't cut it.

Welcome to the Forum. :)
 
infinity said:
IMO you need a mechanical means to keep both units from operating at the same time like a manual transfer switch. A sign won't cut it.

Welcome to the Forum. :)
Click to expand...


Thanks For info.
Makes total sense. I was thinking of accomplishing
this thru the controls. I can install a relay to only allow
one chiller to run.
Also double throw switches are limited to 100amp max I believe.

Worst case would be someone turns both chillers on and the
trip the breaker.

Sure wish there was a section in the code to address this.

Thsnks for your input
 
Double throw switches are not limited to 100 amps, you shouldn't have any problem finding the right size double throw switch.
 
Cow said:
Double throw switches are not limited to 100 amps, you shouldn't have any problem finding the right size double throw switch.
Click to expand...

ive never been happier to be wrong.
You are correct, found a DTNF324 which Can
be used according to Siemens lit as a means
to control two loads. Not cheap, but that’s my problem.

only downside I can see is. Can’t trouble shoot the chiller
thats off while the other one handles the load. You can’t
perform a dry run on controls.

I can see this being a turn off for the customer/tech.

Thanks
 
Ok I can’t do the double throw switch. I won’t have
the face to tell them they can’t view controls
on chiller that’s down because good chiller is
running. But I can install a small 30amp double
throw switch right between both chillers and wire
the enable switch wire from each chiller thru it.

Would this satisfy having a “mechanical interlock “??

also here is a pic of panel layout
 
GoldDigger said:
While not good enough for LOTO, that should be fine to satisfy non-concurrent operation.

Sent from my XT1585 using Tapatalk
Click to expand...

Great that’s half the battle. Would being able to
loto the double throw switch satisfy the lock out part?

The main disconnect feeding both chillers also
can be locked out. I tried to attach pictures but
i think I’m doing something wrong.

Is there a section in the nec that mentions non concurrent loads? Or
mechanical interlock? I’ve read my 2011 nec front to back.

Side note; this site it awesome Can see how many could
benefit from the knowledge shared here. Wish I could offer some to
but its not my expertise. But if anyone has hvac questions I’d be happy to
help. I know that may be for a different forum but u never know.

Thanks
 
farmlife said:
Great that’s half the battle. Would being able to
loto the double throw switch satisfy the lock out part?

The main disconnect feeding both chillers also
can be locked out. I tried to attach pictures but
i think I’m doing something wrong.

Is there a section in the nec that mentions non concurrent loads? Or
mechanical interlock? I’ve read my 2011 nec front to back.

Side note; this site it awesome Can see how many could
benefit from the knowledge shared here. Wish I could offer some to
but its not my expertise. But if anyone has hvac questions I’d be happy to
help. I know that may be for a different forum but u never know.

Thanks
Click to expand...

Would 440.33Ex#1 apply?
 
infinity said:
Would 440.33Ex#1 apply?
Click to expand...

Rob thanks for code. I looked it up and believe
this may be for a scenario where multiple ac’s or compressors
are collectively maintaining a load. Would be like having one chiller
with multiple compressor (but with no info tag on unit to size protection by)

i will keep looking. I know there has to be a code that addresses two loads
on one power source.

Thnks again.
 
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