CSLB C-10 Electrical ContractorEquipment and InstallationHard
A technician is sizing branch-circuit conductors for a hermetic refrigerant motor-compressor. The compressor nameplate lists a rated-load current (RLC) of 22 amperes and a branch-circuit selection current of 26 amperes. Per NEC 440.6, which value must be used to size the branch-circuit conductors?
- AThe average of both values, 24 A
- B26 A (branch-circuit selection current)
- CThe sum of both values, 48 A
- D22 A (rated-load current)
Show answer & explanationAnswer & explanation
Correct answer: B. 26 A (branch-circuit selection current)
NEC 440.6(A) requires that when a branch-circuit selection current is marked on a hermetic refrigerant motor-compressor's nameplate, it must be used instead of the rated-load current for sizing branch-circuit conductors, disconnects, and controllers, since it accounts for the compressor's maximum operating current under all conditions.
Why the other options are wrong
- A. Averaging the two values is not a recognized method in Article 440.
- C. Summing the values grossly oversizes the circuit and is not code-compliant.
- D. RLC is used only when no branch-circuit selection current is marked on the nameplate.
Branch-Circuit Selection Current (440.6)
For hermetic refrigerant motor-compressors, if a branch-circuit selection current is marked on the nameplate, it must be used in place of rated-load current for all branch-circuit sizing calculations.
- Branch-circuit selection current is always ≥ rated-load current when both are marked
- Used for conductor ampacity, disconnect, and controller sizing
- Found in Article 440, which governs air-conditioning and refrigeration equipment
Memory trick: 'When selection current is marked, it always wins the sizing game.'