# MINIMUM breaker size for a 170 ton chiller



## jhall.sparky (Jun 14, 2011)

mmc said:


> We just installed a 170 ton chiller on an office building. The minimum circuit ampacity is 327. The MOCP is 450. I have two 3/0 THHN wires in parallel on each leg back to the breaker. Can anyone tell me the MINIMUM breaker size for this chiller? Thanks for the help.


450 is fine......... how far is the equipment from source?

why two wires running parallel?


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## Dennis Alwon (May 9, 2009)

Well I would guess the minimum would be 350 amps. but I am not sure I would do that-- I would use the MOCP. Never seen a minimum rating for OCPD. You will have problems if you go too low.


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## jhall.sparky (Jun 14, 2011)

what types of compressors are you running ?

whats the make , model of unit/s your using?

not that this matters to you original question just asking!:thumbup:


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## Dennis Alwon (May 9, 2009)

jhall.sparky said:


> what types of compressors are you running ?
> 
> whats the make , model of unit/s your using?
> 
> not that this matters to you original question just asking!:thumbup:


I don't think a chiller has a compressor but I may be wrong.


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## jhall.sparky (Jun 14, 2011)

Dennis Alwon said:


> I don't think a chiller has a compressor but I may be wrong.


 
come on guy im no dud give me some credit............http://www.huffingtonpost.com/2011/07/26/scott-evans-dog-electrocuted_n_909672.html


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## tkb (Jan 21, 2009)

Are the 3/0 parallels in separate conduits?


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## jhall.sparky (Jun 14, 2011)

tkb said:


> Are the 3/0 parallels in separate conduits?


 
probably not........be careful with this thread i have a _HUNCH...................._

_but im up for a challange!!!!!!!!!!!!!!!!!!!_


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## Cletis (Aug 20, 2010)

*hummm*

that's about 15,000 pds. I don't think that will go on top of a building?


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## NolaTigaBait (Oct 19, 2008)

Dennis Alwon said:


> Well I would guess the minimum would be 350 amps. but I am not sure I would do that-- I would use the MOCP. Never seen a minimum rating for OCPD. You will have problems if you go too low.


I would have to agree with this. Its the next standard size....Why not just fuse it @450?....Is this a test question or something....


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## mmc (Aug 16, 2011)

This is a screw chiller with two screw compressors inside a central plant on the ground. The panel is about 15' - 20' from the chiller. I don 't know if our electrical contractor installed it during the change-out, but there is a old 300 amp breaker on this brand new chiller and I see problems coming my way. That's why I'm asking the question about minimum breaker sizing.


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## jhall.sparky (Jun 14, 2011)

mmc said:


> This is a screw chiller with two screw compressors inside a central plant on the ground. The panel is about 15' - 20' from the chiller. I don 't know if our electrical contractor installed it during the change-out, but there is a old 300 amp breaker on this brand new chiller and I see problems coming my way. That's why I'm asking the question about minimum breaker sizing.


there are some great contractors in TEXAS/south (hint hint)....... that can run a load analysis and "tatle Tale" if youd like!

J.HALL


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## jhall.sparky (Jun 14, 2011)

Cletis said:


> that's about 15,000 pds. I don't think that will go on top of a building?


 
not that kind of challange guys sorry! the OP gets it ( I THINK!?!)


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## Dennis Alwon (May 9, 2009)

mmc said:


> This is a screw chiller with two screw compressors inside a central plant on the ground. The panel is about 15' - 20' from the chiller. I don 't know if our electrical contractor installed it during the change-out, but there is a old 300 amp breaker on this brand new chiller and I see problems coming my way. That's why I'm asking the question about minimum breaker sizing.


I would get the EC to change the breaker but as I stated I have never seen a minimum but rather a max and that is what I always use.


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## jhall.sparky (Jun 14, 2011)

Dennis Alwon said:


> I would get the EC to change the breaker but as I stated I have never seen a minimum but rather a max and that is what I always use.


 
alot, NOT ALL, but ALOT of EC's are easily confused especially after the name plate changes inthe mid-90's................ just get a load evaluation.


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## mmc (Aug 16, 2011)

So I gather that based on minimum circuit ampacity, there is no code for minimum breaker size. The thought is that it's OK as long as the breaker doesn't trip? Is that correct? Nothing like minimum ampacity times 1.25? Just as long as it doesn't trip???


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## Dennis Alwon (May 9, 2009)

Well the code does state that the overcurrent device must be sufficient enough to allow the motor to start. I have not found an actual minimum.


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## Dennis Alwon (May 9, 2009)

Actual the motor states the minimum circuit ampacity which is the motor rating plus 25%. This means the circuit breaker must also be at least equal to the MCA


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## jhall.sparky (Jun 14, 2011)

mmc said:


> So I gather that based on minimum circuit ampacity, there is no code for minimum breaker size. The thought is that it's OK as long as the breaker doesn't trip? Is that correct? Nothing like minimum ampacity times 1.25? Just as long as it doesn't trip???


 
no,no,no......... that is not whats being said (WTF are you doing?)...... and please refer to my previous post.

also if the goal is to not have the breaker trip (AGAIN WTF?) then why not just connect it right under the LINE SIDE luggs and just throw the breaker away.........................................................

come on guy just call a pro!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


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## jhall.sparky (Jun 14, 2011)

mmc said:


> we just installed a 170 ton chiller on an office building. The minimum circuit ampacity is 327. The mocp is 450. i have two 3/0 thhn wires in parallel on each leg back to the breaker. can anyone tell me the minimum breaker size for this chiller? Thanks for the help.


 
agian wtf ???????????????????????????????????????

Pictures?????????????????


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## mmc (Aug 16, 2011)

The EC is one of the larger ECs in Houston. I thought they were professional. This no mom & pop setup. I think they are attempting to value engineering the job. I wanted a clear answer to my question based on the facts as stated. The color of the chiller doesn't really matter. Dennis Alwon is the closest to giving me good clear information. I appreciate that very much. At least his information is something that I can go back to the EC and say to him . . . WTF! Get it?


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## will smith (Jul 4, 2011)

*Breaker/fuse/wire sizes for chiller*

I'm just a lowly journeyman service tech that primarily works on commercial hvac equipment (chillers, rtus, boilers), and I certainly don't want to be telling you folks your job, but besides all the formulas you guys have to know for sizing, the chiller manufacturer should tell you exactly what they call for in the Installation-Operations Manual. Proper service sizing is the first thing I check for with the electrician whenever I do a start up on new equipment. The mechanical contractor on the job should be expected to give you access to any and all manuals regarding the equipment's electrical requirements.
All the best


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## mmc (Aug 16, 2011)

I too am just a lowly service tech that takes care of that building and that new chiller. That's why I was concerned when the Carrier literature said "minimum circuit ampacity 327 amps and the EC had a 300 amp breaker. It has since been replaced by a 400 amp breaker and all is good. Thanks for the help.


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## jhall.sparky (Jun 14, 2011)

mmc said:


> The EC is one of the larger ECs in Houston. I thought they were professional. This no mom & pop setup. I think they are attempting to value engineering the job. I wanted a clear answer to my question based on the facts as stated. The color of the chiller doesn't really matter. Dennis Alwon is the closest to giving me good clear information. I appreciate that very much. At least his information is something that I can go back to the EC and say to him . . . WTF! Get it?



Yes I get it....... And color was not the reason I was asking those questions. I just don't believe you. also you have stated that the breaker was "just switched" to a 400 amp huh? And all is
Running well now, how do you know ! Also if the chiller has a combined load of 2.5 m btu/h how. Is it that simply changing a breaker changed performance? Explain . Also if a mom/pop 
Shop is a problem, why didn't you just call WalMart to install it. 


Man I'm just not believing YOU are in charge of this entire buildings automation process and 
You begin by asking if the breaker is ok. 

If that offends you then its time to check out!

J. HALL


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## nitro71 (Sep 17, 2009)

If your contract spelled out the EC installing a breaker I would require him to install the 450. 300 is much less than 450.


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## Control Freak (Mar 8, 2008)

First of all I've done a ton of chillers in the past, 4160v York Johnson Control Chillers with built in drives forward/reverse starters,the works. The outfit I was with worked frequently with mechanical contractors. Where you saw us you saw a horde of fitters shouting for the welders hooked up!

Basic motor control: flc on the name plate to start then 125 % size on all ocpd. That's the basics kid and might I add that the mech. Contractor always furnished a print or a spec sheet at a bare minimum.

Please don't hack hit up and bug nut these splices either! Get a high press lugs 3M motor pigtail kit that you press on the lugs and bolt them together flat side to flat side!
At a minimum get a burndy multitap! 

Wheres the chiller being set? I'll come out and hook it up. For a small fee!....lol!


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## Control Freak (Mar 8, 2008)

Amendment : time delay fuses are a must. Remember in rush current


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## sspeare (Aug 4, 2011)

From the 2008 NEC:

REQUIRED AMPACITY: 440.6(A); 440.7; 440.32; 440.33
DISCONNECT: 440.12(B)(1) and 440.12(B)(2)
MOCP: 440.22
OVERLOADS: 440.52

Hope this helps.


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## nitro71 (Sep 17, 2009)

mmc said:


> The EC is one of the larger ECs in Houston. I thought they were professional. This no mom & pop setup. I think they are attempting to value engineering the job. I wanted a clear answer to my question based on the facts as stated. The color of the chiller doesn't really matter. Dennis Alwon is the closest to giving me good clear information. I appreciate that very much. At least his information is something that I can go back to the EC and say to him . . . WTF! Get it?


Bottom line. The max OCP is usually what is installed. Most don't have a min listed.


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## frenchelectrican (Mar 15, 2007)

nitro71 said:


> Bottom line. The max OCP is usually what is installed. Most don't have a min listed.


It the excat the same methold I done in France we will sized the conductor to min rating if posted otherwise follow the max OCP and go from there and never have a issue if done right in first place.

Merci,
Marc


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