Chiller Service

Status
Not open for further replies.
W

wbaldie

Member
Location
Monroe County
I need a 300 amp 3 phase 480 volt service from an existing 1200 amp panel to feed a chiller but the 1200 amp panel has no more space to add new breakers. I plan to tap the 1200 amp main and place a 300 amp enclosed circuit breaker next to the 1200 amp panel to feed the chiller. What tap rule and wire size would I need from the tap (main) to the enclosed CB? and from the CB to the chiller (3#350Kcm + 1#4EG in conduit?). Please advise on both sizes or if I can do what I asked above.
Thanks
 
The EGC from tap to new breaker enclosure must be sized based on 1,200 amps from table 250.122

A 1200 amp feeder is likely parallel conductors. How are you tapping into all of them?
 
Have you considered going to the transformer? We do these often and rather than upsize the service to the building just to send the chiller load right back out we sometimes opt to set service rated equipment at the chiller and grab the utility transformer. It often is a significant savings.
 
You are right. I suppose I made the assumption that the chiller was not in or on the building. We almost never see that on post.
Below is what I am accustomed to seeing and my suggestion does not work in all cases as stated.

Capture.JPG
 
Just to clarify that it is a feeder that I need for the chiller. My thoughts was to tap the bus and provide an enclosed circuit breaker next to the MDP. The problem as stated before is the panel has no additional space to add a 300 amp breaker and I need to power the chiller from that 1200 amp MDP. I think the transformer is in the same room as the MDP so I will look into the option to come from there. I did not quite understand the disconnect having to be grouped with other disconnects, so I will be doing a little more research on that subject. Thanks to all for your quick responses. The E.C is actually waiting for me to advise him on what direction to take.
 
Tapping "the bus" may or may not be possible depending on the availability of lug kits from the manufacturer. Just drilling your own holes and adding bolts will void the UL listing conditions of the panel.
 
wbaldie said:
Just to clarify that it is a feeder that I need for the chiller. My thoughts was to tap the bus and provide an enclosed circuit breaker next to the MDP. The problem as stated before is the panel has no additional space to add a 300 amp breaker and I need to power the chiller from that 1200 amp MDP. I think the transformer is in the same room as the MDP so I will look into the option to come from there. I did not quite understand the disconnect having to be grouped with other disconnects, so I will be doing a little more research on that subject. Thanks to all for your quick responses. The E.C is actually waiting for me to advise him on what direction to take.
Click to expand...

Forget about the grouping comments as they're not germane to your installation.

You could use or the 10' or 25' tap rule. The 25' rules means that you need tap condcutoars that are at least 1/3 the ampacity of the OCPD ahead of the tap. If you can keep your tap conductors down to 10' or less than you only need to use conductors rated for 10% of the OCPD ahead of the tap.
 
infinity said:
Forget about the grouping comments as they're not germane to your installation.

You could use or the 10' or 25' tap rule. The 25' rules means that you need tap condcutoars that are at least 1/3 the ampacity of the OCPD ahead of the tap. If you can keep your tap conductors down to 10' or less than you only need to use conductors rated for 10% of the OCPD ahead of the tap.
Click to expand...

Yes, but really, if he has a 1200A MDP, we can ASSume the main OCPD is no bigger than 1200A, so if he wants another 300A feeder, he is ALREADY at 25% of the OCPD. So the 10% issue is moot, but the 10' rule does mean the conductors could be just rated for the 300A, not 400A.

wbaldie;
The grouping issue would have been that IF you tapped off of the transformer, and assuming there is a Main CB on your MDP and it is the Service Entrance, then if you tap AHEAD of the MDP, you have to follow the "6 hand rule" for service disconnects, meaning they must all be close enough to each other so that a fire fighter can move his had only 6 times max to kill all power sources. Irrelevant however if you are DOWN stream of the MDP main breaker.

Which brings up an unaddressed issue; DOES your MDP have a main breaker? Or is is an MLO panel with no more than 6 feeders in it? If it is MLO and it IS 6 feeders already, you cannot do this at all.

Next issue: you are increasing your load by 25% of the maximum rating of the MDP, which is already full. Are you sure you have that capacity?
 
Jraef said:
Yes, but really, if he has a 1200A MDP, we can ASSume the main OCPD is no bigger than 1200A, so if he wants another 300A feeder, he is ALREADY at 25% of the OCPD. So the 10% issue is moot, but the 10' rule does mean the conductors could be just rated for the 300A, not 400A.
Click to expand...

Capacity issues aside the 10' or 25' tap rule can be used. As noted the 10' rule allows him to use 300 amps conductors for his 300 amp tap. The 25' would not allow those same conductors. In the OP he asked if you could use 350 kcmil, which he can, but needs to apply to 10' rule along with it.
 
Status
Not open for further replies.
Top