Sizing Chiller Breaker based on MCA/MOP

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kwired

kwired

Electron manager
Location
NE Nebraska
abraves237 said:
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?
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Where are you finding this in 440? I see 175% and 225% but not 125%. 125% maybe for overload protection - but that is not typically provided by the branch circuit device.

The branch circuit device needs to be able to hold during starting, and 175% is often minimum you would ever want for a thermal magnetic breaker on startup of such a load, anything less may trip even though there is nothing wrong.

In your case with multiple compressors you only need to worry about starting current of largest compressor, unless they all can start at same time.
 
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