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Electrical work contracted under C K ELECTRIC · CSLB Lic. #354550 (C-10) · Farmer Works Electric license in process

NEC 250.118 · Homes and commercial

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.

Diagram of equipment ground paths: flex counts only at 6 ft or less and 20 A or less, MC needs a ground wire, EMT counts, building steel does not.
Two common corrections: flex past 6 ft or over 20 A with no wire ground, and standard interlocked MC armor treated as the only ground. Diagram: Farmer Works Electric, free to share under CC BY 4.0 · Download PNG · How to credit

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.
Parallel runs of metal EMT conduit bending into a pull box on a wall
EMT conduit runs into a pull box (representative stock photo).

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

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Electrical work contracted under C K ELECTRIC · CSLB Lic. #354550 (C-10) · Farmer Works Electric license in process