Equipment with Threaded Entries

Article 500 covers the installation requirements in hazardous (classified) locations.

Dec. 10, 2014

For listed explosionproof equipment, factory threaded entries shall be made up with at least _____ threads fully engaged.

a) 4
b) 4.5
c) 5
d) 6

See answer and applicable Code reference

The correct answer is: b) 4.5

Article 500 covers the installation requirements in hazardous (classified) locations. Section 500.8 focuses on equipment. As per 500.8(E)(1), "For equipment provided with threaded entries for NPT threaded conduit or fittings, listed conduit, conduit fittings, or cable fittings shall be used. All NPT threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread. NPT threaded entries into explosionproof equipment shall be made up with at least five threads fully engaged." However, an Exception notes: "For listed explosionproof equipment, joints with factory threaded NPT entries shall be made up with at least 4.5 threads fully engaged."

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.