Understanding NEC 250.110: Grounding Requirements for Fixed Equipment

NEC 250.110: Grounding Requirements for Fixed Equipment

The National Electrical Code (NEC) Section 250.110 specifies the grounding requirements for exposed, non-current-carrying metal parts of fixed equipment. This ensures safety by reducing the risk of electric shock and ensuring proper grounding in hazardous situations. Below is a detailed guide to understanding these requirements.

General Rule

Exposed, non-current-carrying metal parts of fixed equipment must be connected to an equipment grounding conductor in the following conditions:

• Proximity to People and Grounded Surfaces: If within 2.5 m (8 ft) vertically or 1.5 m (5 ft) horizontally of ground or grounded objects and subject to contact by persons.
• Wet or Damp Locations: Located in a wet or damp area and not isolated from contact.
• Electrical Contact with Metal: If in electrical contact with metal.
• Hazardous Locations: If installed in hazardous (classified) locations as per Articles 500–517 of the NEC.
• Supplied by a Grounding Method: If supplied by a wiring method that includes an equipment grounding conductor, except as permitted by 250.86 Exception No. 2.
• Voltage Exceeds 150V to Ground: Equipment operating with terminals over 150 volts to ground.

Exemptions for Non-Critical Grounding

Some exposed, non-current-carrying metal parts that are not likely to become energized do not require grounding. These include:

• Metal nameplates mounted on non-metallic enclosures
• Small parts such as bolts and screws

Exceptions to Grounding Requirements

There are specific cases where grounding may not be required:

1. Electrically Heated Appliances: Metal frames of electrically heated appliances do not require grounding if they are permanently and effectively insulated from the ground. This exemption requires special permission.
2. Distribution Apparatus on Poles: Transformers and capacitor cases mounted on wooden poles at heights exceeding 2.5 m (8 ft) above ground are exempt from grounding.
3. Double Insulated Equipment: Equipment with a system of double insulation or its equivalent does not require grounding. Such equipment must be distinctively marked.

Conclusion

Understanding the grounding requirements of NEC 250.110 is crucial for ensuring the safety of fixed equipment. Proper grounding reduces the risks of electric shock and ensures compliance with electrical codes, especially in hazardous or high-voltage environments. Adhering to these guidelines protects both individuals and equipment.