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

• A. 1 inch or larger
• B. 2 inches or larger
• C. 1/2 inch or larger
• D. 3 inches or larger

Answer: (C)

In hazardous Class I, Division 1 locations, you have to prevent flammable vapors from migrating into electrical enclosures through conduits. Sealing the conduit as it enters a splice box creates a gas-tight barrier that stops flame or hot gases from traveling into the box if a fault occurs, helping to keep the enclosure explosion-protected.

The rule sets a practical threshold: any conduit with a trade size of 1/2 inch or larger must be sealed with a listed sealing fitting at the box entry. This recognizes that larger conduits present a greater potential flame path, so a seal is required. Smaller conduits (less than 1/2 inch) are not required to have this seal at the entry because the risk is lower and typical connectors and the box itself can provide adequate protection.

So, for any conduit entering a splice box in Class I, Division 1 that is 1/2 inch or larger, you would use a listed conduit seal at the entry.