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#220057 05/02/19 05:29 PM
Joined: Mar 2005
Posts: 240
Member
If you have a hydronic heat pump with a minimum ampacity of 23 amps and max of 35 amps wired with mc...wouldn’t sizing the wire to max current make the most sense? Has anyone ever had a problem with sizing motor to minimum ampacity before? Probably should have worded as a code question.

Thanks,
H20

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The bottom line is, "what does the label say" . You don't need to wire any motor load for the locked rotor current because it is only there for a second or less. We wire for 125% of the full load amps. In a complex box like an HVAC system the industry engineers evaluate that box and give you a label for guidance. As an electrician or inspector we should just believe. You can use a #12 for that if everything is rated 75c (breaker, conductors and HVAC lug)


Greg Fretwell
gfretwell #220094 05/27/19 09:35 PM
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I agree with Greg with one exception.
Fire pumps are wired differently because they are expected to run to destruction rather than trip on normal overloads like a regular motor.
The wire sizing is capable of carrying LRA for 20 seconds or more since the motor may have issues getting up to speed.
Nobody wants to console the owner of a burning building by telling them "hey...at least the fire pump motor got tripped offline and is still okay".


Ghost307

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