Sizing Chiller Breaker based on MCA/MOP

[abraves237]

I'd like to apologize in advance if this is a redundant question (I've searched and found similar questions but they have also left me confused).

I have a Trane Chiller that has 4 compressors at RLA=18.6A each. It also has 4 fans at a total FLA=12.6A. It also has some controls, but it doesn't specify the power.

The unit states the MCA=93A and the MOP=110A. I've seen countless ways to get to the MCA and MOP based on the compressor and fan information provided above, but I'd like a clearer answer based off of my specifics if at all possible.

Also, I'm having a little confusion with section 440 of the NEC stating that the breaker should be sized at 125% of the load, or kept at 80% breaker capacity. Is this a calculation that is built into the MCA and MOP?

Long story short, is it acceptable to utilize a 100A breaker for this chiller and not be in violation of the chiller specs or code?

Thanks

 

[iwire]

Long story short yes.

100 is more than the minimum and less than than the maximum.

 

[don_resqcapt19]

When you have a nameplate with the MCA and the MOP you have all of the information that you need. The minimum ampacity of the wire is 83 amps and the maximum size of the OCPD is 110 amps. There is not a code issue with using a 100 amp OCPD, and with the multiple compressors I expect that will be fine.

 

[abraves237]

Thank you for your responses.
Based of the code, how exactly is it applied to my situation so that I can provide proof that the MOP takes the 80% breaker capacity into account?

 

[Fitzdrew516]

Thank you for your responses.
Based of the code, how exactly is it applied to my situation so that I can provide proof that the MOP takes the 80% breaker capacity into account?

There's a lot of confusion when it comes to the whole "80% breaker vs. 100% breaker" thing. What is commonly referred to as an "80% breaker" or just a standard breaker will handle 100% of it's value as long as the load is non-continuous. In your case, the manufacturer listed MOP and MCA have taken into account demand factors such as continuous load, diversity factors, etc. Therefore you shouldn't have to "prove" anything per say.

Check out this quick video; it goes into this concept in depth and explains it well.

http://static.schneider-electric.us/assets/products/circuit-breakers/podcasts/player.html

-Drew

 

[dkidd]

Nameplate trumps any calculation you might make.

 

[texie]

Thank you for your responses.
Based of the code, how exactly is it applied to my situation so that I can provide proof that the MOP takes the 80% breaker capacity into account?

The requirements of the NRTL listing determine the MCA and max OCPD. This may help understanding: http://ul.com/wp-content/uploads/2014/04/EHCMG_AG.pdf
FYI, while I would agree that you could use a 100 amp OCPD in lieu of the the max of 110 amp and be NEC compliant, I would think long and hard about that-especially with a chiller. If it ever trips on start-up those Trane guys will throw you under the bus for sure. I always use the max to avoid finger pointing later.

 

[iwire]

Thank you for your responses.
Based of the code, how exactly is it applied to my situation so that I can provide proof that the MOP takes the 80% breaker capacity into account?

In my opinion it is a moot point if it is taken into account or not. It would be code violation to install a breaker with an ampacity above the listed maximum on the unit.

You could choose to use a 100% rated breaker and enclosure but either way the over current protection chosen cannot exceed the maximum listed on the unit.

 

[Ingenieur]

1.25 x 18.6 + 3 x 18.6 + 12.6 = 91.7
probably thew in a couple amps for the controls (1.3 A controls)
so 93

actual load 4 x 18.6 + 12.6 = 87 + a few amps for control, say 88.5
chances are the next size conductor >93 gives you some more headroom

they say 93
size it for that and use the 110 CB
88.5/110 ~ 80%

#3 awg 100/115 A 75/90 C

100/88.5 ~ 113%
115/88.5 ~ 130%

 

[topgone]

1.25 x 18.6 + 3 x 18.6 + 12.6 = 91.7
probably thew in a couple amps for the controls (1.3 A controls)
so 93

actual load 4 x 18.6 + 12.6 = 87 + a few amps for control, say 88.5
chances are the next size conductor >93 gives you some more headroom

they say 93
size it for that and use the 110 CB
88.5/110 ~ 80%

#3 awg 100/115 A 75/90 C

100/88.5 ~ 113%
115/88.5 ~ 130%

You are wrong in calculating for the maximum overcurrent protection there.
MOP = 2.25 x rated load current of the largest motor + other motor loads + all heater loads
MOP = 2.25(18.6) + 3(18.6) + 12.6 = 110.25 ~ 110A

 

[Ingenieur]

You are wrong in calculating for the maximum overcurrent protection there.
MOP = 2.25 x rated load current of the largest motor + other motor loads + all heater loads
MOP = 2.25(18.6) + 3(18.6) + 12.6 = 110.25 ~ 110A

You are wrong
I was looking at ampacity

then compared it to a selected conductor ampacity
then against the mfgs mop of 110

 

[monsterbuu]

MOCP: 2.25*(18.6)+18.6+18.6+18.6+12.6 = 110.25A
I'd use 110A breaker.

MCA: 1.25*18.6+18.6+18.6+18.6+12.6=88.25A
I'd use #3 AWG (100A) instead of #4AWG (85A) @75degreeC copper.

I'm assuming it's single point connection across the line (no vfd).
the question I have is, what if Trane provided a datasheet stating the MOP and MCA? would i use Trane's values or use the above calculated values?

 

[don_resqcapt19]

MOCP: 2.25*(18.6)+18.6+18.6+18.6+12.6 = 110.25A
I'd use 110A breaker.

MCA: 1.25*18.6+18.6+18.6+18.6+12.6=88.25A
I'd use #3 AWG (100A) instead of #4AWG (85A) @75degreeC copper.

I'm assuming it's single point connection across the line (no vfd).
the question I have is, what if Trane provided a datasheet stating the MOP and MCA? would i use Trane's values or use the above calculated values?

You use the MCA and MOP from the nameplate...you don't do your own calculations when that information is provided on the nameplate.

 

[infinity]

You use the MCA and MOP from the nameplate...you don't do your own calculations when that information is provided on the nameplate.

I agree. If the information is available on the nameplate, as it is with most modern chillers, that's all that you need.

 

[Ingenieur]

I agree. If the information is available on the nameplate, as it is with most modern chillers, that's all that you need.

I don't think anyone suggested otherwise
just speculating on how the ratings were arrived at

 

[infinity]

I don't think anyone suggested otherwise
just speculating on how the ratings were arrived at

Yes it's all good. Don and I were simply responding to monsterbuu who asked "would i use Trane's values or use the above calculated values?"

 

[iwire]

Well I was kind of looking forward to 75 pages arguing of about the right way to calculate what does not need to be calculated.

 

[Ingenieur]

Yes it's all good. Don and I were simply responding to monsterbuu who asked "would i use Trane's values or use the above calculated values?"

Always use mfgs
unless engineering evaluation indicates otherwise
then consult with mfg
then flip a coin lol

 

[don_resqcapt19]

Always use mfgs
unless engineering evaluation indicates otherwise
then consult with mfg
then flip a coin lol

The nameplate information is 110.3(B) and engineering supervision cannot change those values. If you want to use larger conductors and a smaller OCPD, that is fine, but not the other way around.

 

[jumper]

Well I was kind of looking forward to 75 pages arguing of about the right way to calculate what does not need to be calculated.