Understanding NEC Article 660: X-Ray Equipment

NEC Article 660 provides safety standards for the installation, operation, and maintenance of X-ray equipment used in industrial, laboratory, and nonmedical applications. These requirements address electrical safety, grounding, guarding, and the operation of equipment under high-voltage conditions.

Scope of Article 660

This article applies to:

• X-ray equipment used in industrial settings, laboratories, and nonmedical applications.
• Systems operating at any voltage or frequency.

Exclusions:

• Medical and dental X-ray installations, which fall under Article 517, Part V.

Informational Notes:

• Radiation safety is regulated by the Department of Health and Human Services under Public Law 90-602.
• Additional guidelines are available from the National Council on Radiation Protection and Measurements (NCRP).

Key Requirements for X-Ray Equipment

1. Hazardous Locations
   • X-ray equipment must not be installed or operated in hazardous (classified) locations unless specifically identified for such environments.
2. Power Supply and Connection
   • Fixed and stationary X-ray equipment must use approved wiring methods and may connect to circuits rated up to 30 amperes using hard-service cords.
   • Portable and mobile equipment require hard-service cords and may connect to circuits up to 60 amperes.
3. Disconnecting Means
   • A disconnecting device must handle at least 50% of the momentary rating or 100% of the long-time rating of the X-ray equipment.
   • Devices must be within sight of the X-ray control panel unless specific conditions or written safety procedures justify an exception.
4. Conductor and Overcurrent Protection
   • Supply branch-circuit conductors must support at least 50% of the momentary rating or 100% of the long-time rating.
   • Feeder conductors serving multiple X-ray units must meet demand calculations, including the two largest units and 20% of additional units.
5. Guarding and Grounding
   • High-voltage components, including X-ray tubes, must be enclosed in grounded enclosures using suitable insulating materials like oil or gas.
   • Low-voltage cables connected to oil-filled units must have oil-resistant insulation.
6. Installation and Maintenance
   • New, used, or reconditioned X-ray equipment must be of an approved type when installed.
   • Transformers and capacitors integral to X-ray systems are exempt from general NEC requirements for such components (Articles 450 and 460).
7. Control and Safety Features
   • Radiographic and fluoroscopic systems must use interlocks or enclosures to prevent accidental exposure to live parts.
   • Diffraction and irradiation systems must include visible indicators or equivalent means to show when equipment is energized.

Applications of X-Ray Technology

• Industrial Testing: Inspecting welds, detecting cracks or structural defects in materials.
• Laboratory Analysis: X-ray diffraction and irradiation for research and quality control.
• Commercial Use: Fluoroscopy in security systems, such as baggage scanners.

Conclusion

NEC Article 660 ensures safe installation and operation of X-ray equipment in industrial and nonmedical settings. By addressing high-voltage requirements, grounding, guarding, and disconnecting means, the article supports effective and safe use of this technology.