When you need custom holes in an explosion-proof enclosure for your hazardous location installation, the temptation to drill them yourself is real. A hand drill, a few minutes of work, and you’re done—right? Wrong. Field-drilling an explosion-proof enclosure is one of the most dangerous and legally problematic decisions you can make in hazardous location work.
This comprehensive guide explains why field-drilling is prohibited, the critical risks involved, and the proper methods for obtaining custom-drilled explosion-proof enclosures that maintain their safety certifications.
Why Field-Drilling Explosion-Proof Enclosures Is Prohibited
Explosion-proof enclosures (NEMA 7/9, Ex d ratings, and similar designations) are not ordinary metal boxes. They are precisely engineered containment systems tested and certified to contain internal explosions without igniting the surrounding hazardous atmosphere.
The Certification Problem
Every explosion-proof enclosure receives its UL (Underwriters Laboratories) certification as a complete, sealed assembly. This certification evaluates:
- Internal volume and pressure dynamics during an explosion
- Temperature rise from installed components
- Creepage and clearance distances between conductors
- Flame path integrity along all joints and surfaces
- Material specifications and surface finishes
Any modification—including drilling—immediately voids this certification. Once you drill into an explosion-proof enclosure, the UL listing is no longer valid, and you’ve created a product that fails to meet safety standards for hazardous locations.
Why This Matters for Safety
In Class I, Division 1 hazardous locations
