Equipment & SystemsQuestion 260 of 521
For a hermetic motor-compressor with a rated-load current of 18 A, what is the maximum branch-circuit short-circuit/ground-fault protective device, based on the 175% value of NEC 440.22(A)?
a.22.5 A
b.27 A
c.40.5 A
d.31.5 A
Explanation
NEC 440.22(A) sizes the protective device at not more than 175% of the rated-load (or branch-circuit selection) current: 18 x 1.75 = 31.5 A. 22.5 A is 125% (conductor factor), 27 A is 150%, and 40.5 A is 225% (the absolute maximum only where needed to start).
Law Reference: 2023 NEC §440.22Practice all 521 questions free — no signup required.
Related questions on this topic
- On an air-conditioning unit nameplate, what does the 'Minimum Circuit Ampacity (MCA)' value tell the installer?
- The 'Maximum Overcurrent Protective Device' (MOCP or 'Max Fuse/HACR Breaker') rating on an HVAC nameplate specifies what?
- An A/C condensing unit has a compressor rated-load current of 18 A and a fan motor of 2 A. Using the 125%-of-largest-motor-plus-others method, what is the minimum circuit ampacity (MCA)?
- If a motor-compressor (rated-load 18 A) will not start on the 175% device, NEC 440.22(A) permits increasing the protection to a maximum of what value?
- A 30 kVA, three-phase transformer has a 480 V primary (primary current ~36 A). With primary-only protection and no supervised condition, what is the maximum primary overcurrent device using the 125% factor of Table 450.3(B)?
- NEC 450.3(B) overcurrent protection percentages for transformers 1000 V or less are based on what?
Last reviewed: · editorial process
PrepPass Editorial Team · Verified against California CSLB C-10 Electrical Trade Examination · How we review