OCPD for multimotor AC equipment

[cppoly]

How do you interpret 440.22(B)(1):

Where a hermetic refrigerant motor-compressor is the largest load connected to the circuit, the rating or setting of the branch-circuit short-circuit and ground-fault protective device shall not exceed the value specified in 440.22(A) for the largest motor-compressor plus the sum of the rated-load current or branch-circuit selection current, whichever is greater, of the other motor-compressor(s) and the ratings of the other loads supplied.

I can interpret this two ways:

1) Not to exceed the largest compressor RLA (175% - 225% round down) then add remaining RLA then round down.

Example:

49.6A compressor RLA
9.2A fan motor RLA

49.6 x 1.75 = 86.8A , round down = 80A + 9.2A = 89.2 round down = 80A

OR

2) Not to exceed largest compressor RLA (175% - 225%) + remaining RLA then round down.

49.6 x 1.75 + 9.2 = 96A round down = 90A

Thanks

 

[mtnelect]

How do you interpret 440.22(B)(1):

Where a hermetic refrigerant motor-compressor is the largest load connected to the circuit, the rating or setting of the branch-circuit short-circuit and ground-fault protective device shall not exceed the value specified in 440.22(A) for the largest motor-compressor plus the sum of the rated-load current or branch-circuit selection current, whichever is greater, of the other motor-compressor(s) and the ratings of the other loads supplied.

I can interpret this two ways:

1) Not to exceed the largest compressor RLA (175% - 225% round down) then add remaining RLA then round down.

Example:

49.6A compressor RLA
9.2A fan motor RLA

49.6 x 1.75 = 86.8A , round down = 80A + 9.2A = 89.2 round down = 80A

OR

2) Not to exceed largest compressor RLA (175% - 225%) + remaining RLA then round down.

49.6 x 1.75 + 9.2 = 96A round down = 90A

Thanks

Look to the manufacturer's installation manual, since their recommendations take into consideration the advantage of the suction return to cool the motor windings.

 

[mtnelect]

Look to the manufacturer's installation manual, since their recommendations take into consideration the advantage of the suction return to cool the motor windings.

As stated in Section 110.3(B).

 

[Dennis Alwon]

IMO, you round down at the end of the calculation.

 

[cppoly]

Thanks.

Sometimes manufacturer's get it wrong on their spec sheet so you have to calculate the value yourself.

440.22(B)(1) seems ambiguous though.

 

[david luchini]

Your example 1) would be correct.

 

[mtnelect]

That's reason the manufacturer's Installation Manual recommended MCA do not match the manual calculations.