In hazardous locations where metal conduit is required, the conduit MUST be threaded with

• A. NPT threads
• B. BSP threads
• C. UNC threads
• D. Metric threads

Answer: (A)

In hazardous locations, the connection between metal conduit and fittings must form a tight, leak‑proof, mechanically reliable seal. National Pipe Tapered Threads (NPT) are designed as a tapered, pipe‑thread system that, when paired with the appropriate sealant, creates a gas‑ and moisture‑resistant seal. This compatibility and sealing capability are essential to prevent vapors from leaking along the conduit interface, which is critical in explosive environments.

Other thread standards like BSP, UNC, or metric are not used for conduit fittings in these electrical systems and do not guarantee the same seal or fit, so they aren’t suitable for this purpose. Therefore, threaded metal conduit in hazardous locations must use NPT threads.