Grounding requirements for flexible wire distribution boxes

Flexible wire distribution boxes must maintain a continuous, low-impedance grounding path using equipment grounding conductors, pigtails, and proper bonding to ensure safety and NEC compliance.

Key Grounding Principles

1. Equipment Grounding Conductor (EGC)
   • The EGC provides a safe, low-impedance path for fault current to return to the source, allowing overcurrent protective devices to trip quickly in case of a ground fault ( ).
   • All incoming and outgoing EGCs must remain continuously connected, even if a device is removed for maintenance or replacement ( ).
2. Pigtail Connections
   • To maintain continuity, all EGCs in a box are spliced together with a short jumper wire (pigtail) that connects to the device's grounding terminal ( ).
   • This ensures that removing a switch or receptacle does not interrupt the grounding path.
3. Metallic Boxes
   • Metal boxes must be bonded to the EGC system using a dedicated green grounding screw, grounding clip, or listed lug ( ).
   • Self-grounding devices can eliminate the need for a separate pigtail if they make reliable contact with the bonded metal box.
4. Non-Metallic Boxes
   • Non-metallic boxes do not require bonding to the EGC; the EGCs are simply spliced together with a pigtail to the device's green screw terminal ( ).
5. Conduit and Enclosure Bonding
   • All incoming and outgoing conduits should have grounding bushings bonded to the enclosure ( ).
   • Bolted ground connectors must be provided on all enclosures for disconnect switches, pull boxes, and similar equipment, connecting to conduit grounding bushings ( ).
6. Separate Ground Conductors
   • Each feeder and branch circuit should include a separate, insulated green ground conductor connected from the panel ground bus to all connected equipment ( ).
   • Bonding jumpers must be installed across expansion or deflection fittings to maintain continuity ( ).
7. Testing and Verification
   • Continuity tests of all ground cables are required to ensure a reliable path ( ).
   • Grounding electrode system resistance should be tested to verify compliance with safety standards ( ).

Summary

For flexible wire distribution boxes, grounding must ensure a continuous, low-impedance path using EGCs, pigtails, and proper bonding. Metal boxes require dedicated bonding to the EGC, while non-metallic boxes rely on pigtail connections. Conduits, enclosures, and expansion fittings must be bonded, and all connections should be tested for continuity. Following these practices ensures compliance with NEC Article 250 and protects both personnel and equipment from electrical faults ( ).