What can serve as the equipment ground
The NEC lists what may serve as an equipment grounding conductor: a ground wire, certain metal conduit and tubing such as EMT, and some cable armor. Flexible conduit and MC cable qualify only under strict limits.
What the code requires
The code allows these as equipment grounding conductors: a copper, aluminum or copper-clad aluminum wire or busbar; rigid metal conduit, intermediate metal conduit and EMT; the armor of AC cable; the copper sheath of MI cable; cable tray and cablebus; listed continuous metal raceways and gutters; and surface raceway listed for grounding.
Flexible metal conduit counts only with listed fittings, a breaker or fuse of 20 A or less, trade size 1¼ or smaller, and no more than 6 ft of total flex in the ground path. Liquidtight flexible metal conduit needs listed fittings and 6 ft total, with 20 A or less for trade sizes ⅜ to ½, or 60 A or less for ¾ to 1¼ with no ⅜ to ½ flex in the path. Flexible metal tubing needs listed fittings, 20 A or less and 6 ft total.
For flexible metal conduit and liquidtight flexible metal conduit, a wire-type ground or a bonding jumper is required when the conduit is installed for flexibility or to limit vibration, or when it is stainless steel (for liquidtight, when it has a stainless steel core). MC cable counts only if it contains a ground wire, is interlocked armor with a bonding conductor listed and identified as an equipment ground, or has a smooth or corrugated sheath listed and identified for that use.
Grounding electrode conductors and a building's structural steel frame may not be used as equipment grounding conductors.
On the job
- Flexible metal conduit whips longer than 6 ft, or on circuits over 20 A, with no separate ground wire are a common correction.
- Treating the armor alone of standard interlocked MC cable as the ground is a common fail.
Exceptions that matter
- One wire that meets the rules for both a grounding electrode conductor and an equipment grounding conductor may serve as both.
What changed in 2023
The 2023 edition split the section into permitted and not-permitted lists, moving the former 250.121 restrictions into 250.118(B). It now requires a wire-type ground or bonding jumper with stainless steel flexible metal conduit and stainless-core liquidtight flexible metal conduit, and allows a bonding jumper instead of a wire-type ground where flex is installed for flexibility.
Related sections
- NEC 250.102(E)
- NEC 250.119
- NEC 250.122: Sizing the equipment ground wire
- NEC 330.108
- NEC 348.60
- NEC 350.60
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