In Class I, Division 1 locations, the conduit to a splice box must be sealed if the trade size is 2 inches or larger.

• A. 1/2 inch or larger
• B. 2 inches or larger
• C. 1 inch or larger
• D. 2 1/2 inches or larger

Answer: (B)

In hazardous locations, wiring must be protected to prevent ignition of flammable vapors. Sealing the conduit at the point it enters a splice box stops any gas or vapors from migrating into the box and prevents flame from traveling through the conduit in case of an ignition. The risk increases with larger conduit sizes because a bigger conduit provides a bigger path for gas flow and for heat or an arc to reach the box. For Class I, Division 1 locations, the rule specifically requires a sealed entry when the conduit trade size is two inches or larger, which is why that threshold is used. Smaller conduits don’t fall under this particular sealing requirement, though other protective measures still apply.