Mechanical room receptacle box
What's wrong here?
- The bonding pigtail is fastened to the box with a sheet-metal screw, not a grounding screw
- A wire-type equipment grounding conductor is not allowed in EMT, since the conduit is the ground
- Equipment grounding conductors may not be spliced with twist-on wire connectors
- Nothing. This installation is compliant
Show the answer and the code reference
The answer
The green bonding pigtail is attached to the metal box with a self-tapping sheet-metal screw instead of a 10-32 grounding screw in the tapped hole or a listed grounding device.
Correct choice: 1. The bonding pigtail is fastened to the box with a sheet-metal screw, not a grounding screw
250.148(C) requires the EGC-to-metal-box connection to be made with a grounding screw used for no other purpose, equipment listed for grounding, or a listed grounding device. 250.8(A) lists the permitted connection means, including machine screws that engage at least two threads or are secured with a nut, and thread-forming machine screws that engage at least two threads; a coarse-thread sheet-metal screw in a drilled hole is neither. In thin box steel that screw catches less than two threads, so it can loosen under vibration and corrode. Here the EMT still bonds the box, so the immediate hazard is low, but in a box fed by nonmetallic raceway or cable that screw would be the only bond. The box already has a tapped grounding boss for exactly this connection.
How to fix it
Remove the sheet-metal screw and land the pigtail under a green 10-32 grounding screw in the tapped GRD hole. A listed grounding clip on the box edge also works.
Code references
NEC 2023 250.8(A) — Permitted Methods
EGCs, GECs and bonding jumpers shall be connected by listed pressure connectors, terminal bars, pressure connectors listed as grounding and bonding equipment, exothermic welding, machine screw-type fasteners engaging at least two threads or secured with a nut, thread-forming machine screws engaging at least two threads in the enclosure, connections that are part of a listed assembly, or other listed means.
Drills citing 250.8(A)NEC 2023 250.148(C) — Metal Boxes
A connection shall be made between the equipment grounding conductor(s) and a metal box by means of a grounding screw used for no other purpose, equipment listed for grounding, or a listed grounding device.
Drills citing 250.148(C)
2026 NEC:changed: The 2026 NEC adds "grounding and bonding terminations" to the opening text of 250.8(A), so the listed connection methods now clearly cover where the conductor is attached to the equipment, not just the conductors. This backs up the drill's answer: a self-tapping sheet-metal screw is still not a permitted method. Confidence: medium
Minnesota
Minnesota adopts the NEC as published, with no section-by-section amendments (Minn. Stat. 326B.35; Minn. Rules 1315.0200), so 250.8 and 250.148 read the same as in the 2023 NEC. The 2023 NEC governs permits filed from July 1, 2023 until the 2026 NEC took effect; for newer permits, check the section numbers in the 2026 edition.
How Minnesota adopts the NECWhy the other choices are wrong
- A wire-type equipment grounding conductor is not allowed in EMT, since the conduit is the ground. EMT is a recognized EGC under 250.118, but nothing prohibits also pulling a wire-type EGC, and many specs require one.
- Equipment grounding conductors may not be spliced with twist-on wire connectors. 250.148(A) and 250.8(A) allow EGC splices with listed pressure connectors, and green twist-on connectors listed for grounding are common.
- Nothing. This installation is compliant. The box bonding connection relies on a self-tapping sheet-metal screw, which is not one of the connection methods 250.8(A) permits.