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MOCP < 125% FLA

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RigusTheo

Electrical
Mar 21, 2024
1
thread237-194364

Good afternoon,

I come across this situation all the time and I wanted to see if anyone here had a response to how they handle it. Very often I come across HVAC equipment that lists FLA/RLA, MCA and MOCP, where the MOCP listed is actually <125% FLA.

Now I know MOCP is often referred to as being calculated as (225% largest load + 100% remaining loads) and then round DOWN to the next standard size. What I don't understand is how this is really a "complete framework" of thinking, so to speak. One consideration for example is that most overcurrent protection is 80% rated such that if this HVAC package is a continuous load, I can't select overcurrent protection where the FLA > 80% OCPD. Yet often this will end up in conflict with the vendor's listed MOCP which is often smaller than 125% FLA.

Any thoughts from anyone? Have a great day.
 
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If you are under the NEC, you use whatever is listed by the manufacturer for MCA and MCOP. Pretty simple. The rest is not relevant. If you are using 125% of the largest motor, you don't need to limit the breaker loading to 80%. 80% is the inverse of 125%. If you size everything per the NEC, the 80% continuous loading for breaker is accounted for by the 125% factor already applied.

Also it's possible that not all motors or loads in an HVAC package run simultaneously. If you use breakers larger than the MCOP, that's an NEC violation.
 
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