Chiller Feeder Calculation
- Thread starter mull982
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Please try to stay on topic. The OP was about the NEC load calculation, so it doesn't matter what you think is overkill or what might/should be or if the compressor has polka dots on it.
I do not believe the article in my last post is against the intent of NEC or is not on topic.
- Location
- Connecticut
- Occupation
- Engineer
The article isn't relevant to Chillers. Nor does it completely follow the NEC.
Please clarify, if possible.
That is AHJ's call.
- Location
- Connecticut
- Occupation
- Engineer
The original question was about Chillers. The article you linked is about Air Conditioners.
No it's not. The NEC tells you how to calculate MCA and MOCP. The article you linked doesn't follow the NEC requirements.
Thanks for your response. I wonder whether i)NEC distinguishes between air conditioner and chiller and ii)UL or third party certifying authority would pass a product design also based on this article and so the AHJ because there is no violation of intent of NEC ie there is no danger to life and property.
- Location
- Connecticut
- Occupation
- Engineer
No (except for the special provisions for room air-conditioners.) It distinguishes between motor operated equipment with a heretic refrigerant motor-compressor and equipment without.
Nobody would pass a product design based on this article. It's just an article, and not a very good one.
Sorry, it is not clear how the article is not applicable to ''chillers''.
UL or other third party certifying agency would test such a product design anyway for any danger to life and property. There would be none.......
- Location
- Connecticut
- Occupation
- Engineer
It doesn't mention "chillers" anywhere in the article. Where would you find a chilled water chiller?
They would test a product to UL standards, not to what this article says.
UL 1995 36.14 seems to be the US standard for determining equipment MCA:
Minimum Circuit Ampacity
36.14 The minimum circuit ampacity (MCA) required by Clause 36.3(h) shall be determined as follows. All
concurrent load conditions are to be considered in the determinations, see Figure 36.1. Whichever load
condition provides the highest value shall be used.
a) For a motor group only, a load consisting of two or more motors, the rated current of the largest
motor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by 125
per cent, added to the rated currents of all of the other motors.
b) For a combination load, a load consisting of one or more motors, electric heaters, and any other
loads, that incorporates one or more compressor motors, the rated current of the largest motor
compressor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by
125 per cent, added to which shall be the value obtained by multiplying the rated current of the electric
heaters by 125 per cent, and adding to that total the sum of the ratings of all other loads.
c) For a combination load, a load consisting of one or more motors, electric heaters, and any other
loads, not involving a hermetic refrigerant motor compressor, the sum of the rated currents multiplied by
125 per cent.
Exception: The rated current of the heater load may be multiplied by 100 percent, rather than 125 per cent,
provided that
1) the rated heater load at a field wiring terminal is 50 kW or more;
2) the minimum conductor size that may be field-connected to such terminal is still to be marked;
and
3) the heater element circuits connected to the field wiring terminals are subdivided as specified in
Clause 30.8 and are arranged to be controlled by one or more temperature-actuated devices to
reduce the likelihood of continuous simultaneous operation of all of the element circuits.
Also, it looks like nameplate motor currents aren't always used to calculate MCA;
https://www.titus-hvac.com/softwares/MOPulator/pdf/howwecalculate.pdf
Minimum Circuit Ampacity
36.14 The minimum circuit ampacity (MCA) required by Clause 36.3(h) shall be determined as follows. All
concurrent load conditions are to be considered in the determinations, see Figure 36.1. Whichever load
condition provides the highest value shall be used.
a) For a motor group only, a load consisting of two or more motors, the rated current of the largest
motor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by 125
per cent, added to the rated currents of all of the other motors.
b) For a combination load, a load consisting of one or more motors, electric heaters, and any other
loads, that incorporates one or more compressor motors, the rated current of the largest motor
compressor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by
125 per cent, added to which shall be the value obtained by multiplying the rated current of the electric
heaters by 125 per cent, and adding to that total the sum of the ratings of all other loads.
c) For a combination load, a load consisting of one or more motors, electric heaters, and any other
loads, not involving a hermetic refrigerant motor compressor, the sum of the rated currents multiplied by
125 per cent.
Exception: The rated current of the heater load may be multiplied by 100 percent, rather than 125 per cent,
provided that
1) the rated heater load at a field wiring terminal is 50 kW or more;
2) the minimum conductor size that may be field-connected to such terminal is still to be marked;
and
3) the heater element circuits connected to the field wiring terminals are subdivided as specified in
Clause 30.8 and are arranged to be controlled by one or more temperature-actuated devices to
reduce the likelihood of continuous simultaneous operation of all of the element circuits.
Also, it looks like nameplate motor currents aren't always used to calculate MCA;
https://www.titus-hvac.com/softwares/MOPulator/pdf/howwecalculate.pdf
NEC requirements for air conditioners (other than room air conditioners) and chillers are same. So the article about air conditioners is also about chillers.
The calculations in the article are based on UL standard. ( Post#31).
kwired
Electron manager
- Location
- NE Nebraska
Mostly yes, if there is hermetic compressors involved art 440 usually applies.
Ok I was finally able to track down the datasheets for these chillers. Chiller rated capacity is 348 (assuming tons) with 205kW at rated 100% load.
The datasheet gives the following: Compressor RLA = 124/158A, MCA=321A, MOP=450A. (3) identical chillers with these values.
I'm not quite sure what the RLA would be provided with (2) different values? These would lead to two very different feeder calcs.
New Feeder Calc using 124A RLA will be: 321A + 124A + 124A = 569A
New Feeder Calc using 158A RLA will be: 321A + 158A + 158A = 637A
Am I looking at these feeder calcs right based off of this new information? Which RLA value to use will have a pretty significant impact in that it will determine weather we are over/under the 600A threshold which will have impact on breaker rating, ATS rating, etc......
Thanks for the help!
The datasheet gives the following: Compressor RLA = 124/158A, MCA=321A, MOP=450A. (3) identical chillers with these values.
I'm not quite sure what the RLA would be provided with (2) different values? These would lead to two very different feeder calcs.
New Feeder Calc using 124A RLA will be: 321A + 124A + 124A = 569A
New Feeder Calc using 158A RLA will be: 321A + 158A + 158A = 637A
Am I looking at these feeder calcs right based off of this new information? Which RLA value to use will have a pretty significant impact in that it will determine weather we are over/under the 600A threshold which will have impact on breaker rating, ATS rating, etc......
Thanks for the help!
- Location
- Connecticut
- Occupation
- Engineer
The chiller has two compressors. One with 124A RLA, one with 158A RLA.
321A+282A+282A=885A
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