Class I Locations — Wiring Methods and Seals

Explosionproof does not mean nothing can explode inside; it means the enclosure contains the blast and cools the escaping gases below ignition. Seals at boundaries and at enclosures keep the raceway from becoming a fuse to the next room.

I pour every seal-off the way the fitting is listed, packed and filled correctly. A dry or skipped seal turns the whole conduit system into a path for a fireball.

When it applies

Class I locations involve flammable gases or vapors. Wiring here uses explosionproof enclosures and threaded rigid methods, and conduit seals are placed to stop a flame or pressurized gas from traveling through the raceway between areas.

Common mistakes

• Omitting or wrongly locating seal fittings. A seal within the required distance of the enclosure is what contains an internal ignition.
• Pouring the seal without the fiber dam, so the compound runs down the conduit and leaves an empty fitting.
• Using standard fittings and thinking the classified boundary is somewhere it is not.

In the field

In a solvent-handling room I found a seal fitting that had been installed but never packed and poured, just an empty coupling with threads. Under a fault that conduit would have carried flame straight into an unclassified space. I dammed it, poured it to the correct depth, and documented it. In Class I, the seal is not paperwork; it is the wall that keeps an explosion in one box.