HVAC mca & mop

[John165]

I was recently told that the mca is for the engineer load calcs, and that mop is what should be used for wire going to unit & breaker size. Is this correct? It kinda makes sense why else would there 2 values? Thanks John

 

[don_resqcapt19]

That is not correct. The minimum circuit ampacity is used for sizing the conductors. The maximum overcurrent protective device is used to size the OCPD. It has a higher value than the MCA to account for inrush current and avoid tripping on start up.

 

[John165]

So if I have an hvac 30 amp mca & an mop of 45 amps I would use #10 wire on a 45 amp breaker?

 

[don_resqcapt19]

So if I have an hvac 30 amp mca & an mop of 45 amps I would use #10 wire on a 45 amp breaker?

yes

 

[John165]

O.K. But I thought that you could only put 10ga wire on a 30amp breaker.

 

[LarryFine]

O.K. But I thought that you could only put 10ga wire on a 30amp breaker.

Start at NEC 240.4 D and G.

 

[infinity]

O.K. But I thought that you could only put 10ga wire on a 30amp breaker.

No. For motor and AC loads you can exceed the ampacity rating of the conductor with the size of the OCPD ahead of it.