Choose the best answer:

What is the minimum size overcurrent protection device (OCPD) required for an A/C unit with a compressor rated at 20A and a condenser rated at 2.5A?
(a) 30A
(b) 35A
(c) 40A
(d) 45A 
What is the maximum size OCPD allowed for an A/C unit with a compressor rated at 20A and a condenser rated at 2.5A?
(a) 30A
(b) 35A
(c) 40A
(d) 45A 
What is the minimum size OCPD required for a 230V, 3phase feedercircuit with the following loads:

A/C unit with a compressor rated at 29A and a condenser rated at 2.5A

A/C unit with a compressor rated at 26A and a condenser rated at 2.5A

A/C unit with a compressor rated at 22A and a condenser rated at 2.5A
(a) 100A
(b) 110A
(c) 125A
(d) 150A 

What is the maximum size OCPD required for a 230V, 3phase feedercircuit with the following loads:

A/C unit with a compressor rated at 29A and a condenser rated at 2.5A

A/C unit with a compressor rated at 26A and a condenser rated at 2.5A

A/C unit with a compressor rated at 22A and a condenser rated at 2.5A
(a) 100A
(b) 110A
(c) 125A
(d) 150A 

What size OCPD is required for a 230V, 3phase feedercircuit with the following loads:

A/C unit with a compressor rated at 26A and the condenser rated at 2.5A

A/C unit with a compressor rated at 24A and the condenser rated at 2.5A

10 hp, 230V, threephase, Design letter B motor
(a) 100A
(b) 110A
(c) 125A
(d) 150A 
answers and discussion

(b), 35A. When calculating the minimum size OCPD for hermetic seal compressors, use a factor of 175% of the compressor FLA rating or branchcircuit selection circuit current — whichever is greater.
Step 1: 20A x 175%+ 2.5A = 37.5A
Solution: 37.5A requires you to use a 35A OCPD.
Stallcup's Code Loop: Secs. 2403(g), 2406(a), and 44022(a). 
(d), 45A. When calculating the maximum size OCPD for hermetic seal compressors, use a factor of 225% of the compressor FLA rating or branchcircuit selection circuit current — whichever is greater.
Step 1: 20A x 225%+ 2.5A = 47.5A
Solution: 47.5A allows you to use a 45A OCPD.
Stallcup's Code Loop: Secs. 2403(g), 2406(a), and 44022(a). 
(a), 100A. The NEC requires you to size the OCPD for a feedercircuit supplying two or more airconditioning units to allow the largest unit to start at one time and the other units to start at different intervals. If there are two or more hermetically sealed motors installed on the same feedercircuit, you must size them at 175% of the fullload current rating of the nameplate or branchcircuit selection current rating of the largest motor — whichever is greater.
Step 1: 29A x 175%+ 2.5A = 53.25A
Step 2: 53.25A + 26A + 2.5A + 22A + 2.5A = 106.25A.
Solution: 106.25A requires a 100A OCPD.
Stallcup's Code Loop: Secs. 2403(g), 2406(a), 44022(a), and 44022(b)(1). 
(b), 110A. You may size the OCPD up to 225% of the motorrated load current or branchcircuit selection current for hermetically sealed motors to allow the motor to start. You typically do this when the motor will not start and develop speed when applying a lower rating, which is normally selected at 175% or less.
Step 1: 29A x 225%+ 2.5A = 67.75A
Step 2: 67.75A + 26A + 2.5A + 22A + 2.5A = 120.75A
Solution: 120.75A requires a 110A OCPD.
Stallcup's Code Loop: Secs. 2403(g), 2406(a), 44022(a), and 44022(b)(1). 
(c), 125A. When installing hermetically sealed motors and other loads (such as motors) on the same circuit, and the largest load in the group is a motor, you must size the OCPD based on the percentages shown in Table 430152.
Step 1: 28A x 250% = 70A
Step 2: 70A+ 26A + 2.5A + 24A + 2.5A = 125A
Solution: 125A requires you to use a 125A OCPD.
Stallcup's Code Loop: Secs. 2403(g), 2406(a), 44022(a), 44022(b)(1), 43052(c)(1), and Tables 430150 and 430152.
Note: A smaller OCPD can be used than the minimum calculated size of the unit.
Stallcup's Code Loops
Each quiz on the 1999 National Electrical Code is provided with Stallcup's Code Loops to show the direct correlation with other sections of the NEC. This allows the reader to review other sections of the NEC when determining if the correct answer to a problem is in one or multiple sections of the Code.