10.1 Equipment Grounding Conductor (EGC) Types, Identification & Sizing (NEC Table 250.122)

10.1 Equipment Grounding Conductor (EGC) Types, Identification & Sizing (NEC Table 250.122)

Quick Answer: An Equipment Grounding Conductor (EGC) is the low-impedance electrical path that connects normally non-current-carrying metal enclosures, raceways, and equipment frames back to the electrical source (system grounded conductor or grounding electrode conductor) per NEC Article 100 and 250.4(A)(3). Wire-type EGCs are sized according to NEC Table 250.122 based on the rating of the overcurrent protective device (OCPD) protecting the circuit. EGCs sized 6 AWG and smaller must be manufactured with green insulation, green with yellow stripes, or bare (field tape re-identification is prohibited per NEC 250.119). For parallel runs in separate conduits, a full-sized EGC must be pulled in each raceway per NEC 250.122(F)(1).

While grounding electrode conductors (GECs) connect an electrical system to the earth for voltage stabilization and lightning dissipation, the equipment grounding conductor (EGC) performs the everyday life-safety work of clearing electrical short circuits. If an ungrounded phase conductor frays and contacts a metallic junction box, motor frame, or appliance chassis, the EGC provides the mandatory, low-impedance return circuit that carries tens or hundreds of amperes of fault current back to the panelboard, instantaneously tripping the circuit breaker or blowing the fuse.

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Permitted Types of Equipment Grounding Conductors: NEC 250.118

Electricians frequently assume an equipment grounding conductor must always be a separate green copper wire. In commercial and industrial construction, however, the National Electrical Code recognizes 14 distinct metallic wiring methods as qualifying equipment grounding conductors under NEC Section 250.118.

Detailed Analysis of Permitted Types

1. Wire-Type Conductors (NEC 250.118): Copper, aluminum, or copper-clad aluminum conductors. They may be bare, covered, or insulated. When installed in nonmetallic raceways (such as Schedule 40/80 PVC or RTRC), a wire-type EGC is mandatory.
2. Rigid Metal Conduit (RMC) & Intermediate Metal Conduit (IMC) (NEC 250.118): Heavy-wall steel or aluminum threaded conduits provide an exceptional, low-resistance metallic fault path that easily satisfies all EGC requirements without pulling a supplemental wire.
3. Electrical Metallic Tubing (EMT) (NEC 250.118): Thin-wall steel EMT is one of the most widely used raceways in commercial facilities. When assembled with listed steel or die-cast compression or set-screw fittings wrench-tightened to manufacturer torque, EMT is recognized as a complete standalone EGC.
4. Flexible Metal Conduit (FMC) (NEC 250.118): Standard "Greenfield" flexible conduit is permitted to serve as the sole EGC only when all of the following conditions are met:
   • The conduit is terminated in fittings listed for grounding.
   • The conduit is not larger than trade size 1¼.
   • The circuit conductors contained in the conduit are protected by an overcurrent device rated at 20 amperes or less.
   • The combined length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same ground return path does not exceed 6 feet (1.8 m).
   • The conduit is not installed to minimize vibration or to allow movement after installation; where flexibility is needed (for example, a vibrating motor hookup), a separate wire-type EGC is required.
5. Liquidtight Flexible Metal Conduit (LFMC) (NEC 250.118): Listed LFMC is permitted as the sole EGC only where the total length in the ground return path does not exceed 6 feet, listed fittings are used, and:
   • For 3/8-inch through 1/2-inch trade size, the circuit is protected at 20 amperes or less.
   • For 3/4-inch through 1-1/4-inch trade size, the circuit is protected at 60 amperes or less.
   • LFMC larger than trade size 1¼, or installed where flexibility is needed after installation, requires a separate wire-type EGC.
6. Type AC Armored Cable (NEC 250.118 & 320.108): Traditional Type AC (BX) cable has an interlocked metal armor with an internal aluminum bonding strip in intimate contact with the armor for its entire length (320.100). The armor and bonding strip together form the EGC path. At terminations, the bonding strip is typically folded back over the armor under the fitting, following the manufacturer's instructions.
7. Type MC Metal-Clad Cable (NEC 250.118): Standard interlocked metal-clad cable (MC) armor is not an approved EGC because the spiraled convolutions introduce high electrical resistance under fault surges. Standard MC cable relies on an internal green insulated copper conductor. However, interlocked MC cable whose combined armor and uninsulated grounding/bonding conductor is listed and identified as an EGC (often sold as MCAP or similar) qualifies under 250.118, as does smooth or corrugated tube-type MC whose sheath is listed and identified as an EGC.

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Conductor Identification Rules: NEC 250.119

The National Electrical Code enforces strict conductor color-coding to prevent installers from accidentally energizing equipment grounding conductors or mistaking an ungrounded phase for a safety ground.

The 6 AWG Cutoff Rule

A critical rule tested on state examinations is the cutoff between small and large conductors:

• An electrician cannot take a black, white, or red 12 AWG or 10 AWG conductor and wrap green phase tape around the ends to make it an equipment grounding conductor. It is an immediate violation of NEC 250.119. In conduit wiring 6 AWG and smaller, the wire insulation must be manufactured green or bare.
• Narrow Exception (NEC 250.119(B)): In multiconductor cable assemblies (such as 12/2 or 10/3 NM or MC cable), an insulated conductor with a continuous green finish is strictly reserved for EGC use, but where qualified service personnel maintain an industrial installation, conductors in cables can be permanently marked with green tape.
• For conductors 4 AWG and larger, field re-identification is fully permitted at the time of installation at every termination and point of access (junction boxes, pull boxes, disconnects) by applying green tape encircling the conductor, painting the exposed insulation green, or completely stripping the insulation from the entire exposed length.

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Sizing Equipment Grounding Conductors: NEC Table 250.122

Wire-type equipment grounding conductors are sized based exclusively on the rating or setting of the overcurrent protective device (fuse or circuit breaker) protecting the circuit conductors, as codified in NEC Table 250.122.

Table 250.122 has no separate 30 A or 40 A rows; read the "not exceeding" column, so a 30 A or 40 A OCPD uses the 60 A row (10 AWG copper). The EGC also never has to be larger than the circuit conductors supplying the equipment.

Key Patterns in Table 250.122

Candidates must commit these foundational breakpoints to memory:

• 15A: 14 AWG Cu
• 20A: 12 AWG Cu
• 30A, 40A, and 60A: All three ratings use 10 AWG copper (or 8 AWG aluminum).
• 100A: 8 AWG Cu
• 200A: 6 AWG Cu
• 400A: 3 AWG Cu
• 800A: 1/0 AWG Cu
• 1200A: 3/0 AWG Cu

Conductor Size Restriction: NEC 250.122(A)

Under NEC 250.122(A), an equipment grounding conductor is never required to be larger than the circuit ungrounded conductors supplying the equipment. For example, if a 40-ampere overcurrent device supplies a circuit wired with 10 AWG copper conductors (permitted under specific motor or welder provisions), the EGC is not required to be larger than 10 AWG copper.

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Multiple Circuits in the Same Raceway: NEC 250.122(C)

In commercial wiring, branch circuits are frequently bundled into a single home-run conduit back to the panelboard. For example, a 1-inch EMT run might contain four 20-ampere lighting circuits and one 50-ampere commercial appliance feeder.

Under NEC Section 250.122(C):

Where a single equipment grounding conductor is run in a raceway, cable, or cable tray containing multiple circuits, it shall be sized for the largest overcurrent device protecting conductors in the raceway, cable, or cable tray.

• The installer is not required to pull five separate green wires through the raceway.
• A single common equipment grounding conductor satisfies the safety requirement.
• In the example above, the largest overcurrent device is 50 amperes. Referring to Table 250.122, a 50-ampere overcurrent device requires a 10 AWG copper EGC. Therefore, a single 10 AWG copper wire protects all five circuits.

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Parallel Feeders in Separate Raceways: NEC 250.122(F)

One of the most heavily tested and widely misunderstood sections of Article 250 is the sizing of equipment grounding conductors in parallel conductor installations.

The Mandatory Full-Size Rule (NEC 250.122(F)(1))

Where conductors are installed in parallel in multiple raceways or cables as permitted by 310.10(G) (2023 numbering):

• An equipment grounding conductor, where installed, shall be installed in each raceway or cable.
• Each equipment grounding conductor must be sized based on the full rating of the overcurrent protective device protecting the conductors in the raceway or cable, in accordance with Table 250.122.

Why Can't the EGC Be Split Proportionally?

Apprentices often calculate the total required EGC circular mils and divide by the number of parallel conduits. For a 1,200A breaker, Table 250.122 requires 3/0 AWG copper (167,800 cmil). Dividing 167,800 cmil by 3 gives 55,933 cmil (approx. 2 AWG).

• The Catastrophic Physics: If a ground fault occurs inside Conduit 1, fault current will flow down the phase conductor in Conduit 1 directly into the faulted enclosure. Fault current does not divide equally across all three conduits; the vast majority of current seeks the immediate return path inside Conduit 1 due to mutual inductive coupling.
• If Conduit 1 contains an undersized 2 AWG copper wire, the extreme ground-fault current (thousands of amperes) will melt and vaporize the 2 AWG wire before the 1,200-ampere breaker can magnetically trip, causing an catastrophic arc-blast fire.
• Therefore, NEC 250.122(F)(1) mandates a complete, full-sized 3/0 AWG copper EGC inside EACH of the three parallel raceways.

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Motor Branch Circuits & Table 250.122

Motor branch circuits present a unique sizing scenario because NEC Article 430 Part IV permits motor branch-circuit short-circuit and ground-fault protective devices (inverse-time circuit breakers) to be sized at up to 250% of motor full-load current (NEC Table 430.52).

• Sizing Rule: The equipment grounding conductor must be sized per Table 250.122 based on the rating of that oversized branch-circuit breaker or fuse.
• Example: A 15-horsepower, 208-volt, 3-phase motor has a full-load current of 46.2 amperes (Table 430.250). The branch circuit conductors are sized at 125% ($46.2\text{ A} \times 1.25 = 57.75\text{ A}$), requiring 6 AWG THHN copper conductors. An inverse-time circuit breaker is sized at 250% ($46.2\text{ A} \times 2.50 = 115.5\text{ A}$), leading to a standard 125-ampere circuit breaker per 240.6(A).
• Sizing the EGC for the 125A breaker from Table 250.122 requires a 6 AWG copper EGC.
• Under 250.122(A), if a calculation ever called for an EGC larger than the 6 AWG branch-circuit conductors, the EGC would not be required to exceed 6 AWG.