New York State Master Electrician Practice Exam

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When using #12 THHN or THWN wire, what is the maximum overcurrent protection allowed for general wiring according to the relevant table?

15A fuse or circuit breaker
20A fuse or circuit breaker
25A fuse or circuit breaker
30A fuse or circuit breaker

The correct answer is: 20A fuse or circuit breaker

When using #12 THHN or THWN wire, the maximum overcurrent protection allowed for general wiring is 20A. This is based on the National Electrical Code (NEC) guidelines, which specify that the maximum overcurrent protection device size for conductors must not exceed certain ratings to prevent overheating and potential fire hazards. For #12 wire, the ampacity is typically rated at 20A for general use, which determines the maximum size of the fuse or circuit breaker that can be used. Selecting a protection device larger than this capacity could lead to a situation where the wiring does not adequately protect against overcurrent, potentially resulting in hazardous conditions, such as overheating. Understanding these limits is crucial for safe electrical design and installation, making it important for electricians to refer to the relevant tables in the NEC when determining appropriate ampacities and overcurrent protection ratings. This ensures the safety and compliance of electrical installations.