The NEC requires conduit and fittings installed in hazardous locations to be wrench-tight with a minimum of how many engaged threads?

• A. 3
• B. 4
• C. 6
• D. 5

Answer: (D)

In hazardous locations, joints must be tight enough to resist vibration and maintain the enclosure’s protective integrity. The NEC specifies that threaded conduit fittings tightened with a wrench must have a minimum engagement of five full threads. This amount of thread engagement ensures a secure, vibration-resistant connection that preserves the flame-path and prevents leaks or looseness over time. Fewer than five threads increases the risk of loosening, while more than five isn’t required by the code.