Which threshold triggers sealing conduits to splice boxes in Class I, Division 1 locations?

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

Answer: (B)

In hazardous Class I, Division 1 locations, controlling the flame path is essential. When a conduit enters a splice box, any ignition within the box could travel along the conduit and ignite vapors outside the box if the path isn’t properly sealed. The rule is that sealing is required when the conduit penetrates into the box by two inches or more. Applying a listed conduit seal at that interface prevents flames or hot gases from moving from inside the box into the conduit and vice versa, helping keep the surrounding area safe.

So, if the conduit into the splice box is two inches or longer, you must seal it. If the penetration is less than two inches, a seal isn’t required by this rule.