8.1 Equipment Grounding Conductors (EGC) Types, Installation & Sizing (Table 250.122)

8.1 Equipment Grounding Conductors (EGC) Types, Installation & Sizing (Table 250.122)

The Equipment Grounding Conductor (EGC) is the backbone of electrical personnel protection and system safety. While the grounding electrode conductor (GEC) connects the electrical system to the physical earth for surge and lightning dissipation, the EGC performs the vital life-safety mission: providing a permanent, low-impedance path to return ground-fault current directly to the electrical source to instantaneously trip the circuit breaker or blow the fuse.

Governed by NEC Article 250, Part VI (Equipment Grounding and Equipment Grounding Conductors), mastering EGC types, identification standards, Table 250.122 sizing, and the mandatory proportional adjustment rule under NEC 250.122(B) is essential for passing the Idaho Journeyman Electrician examination.

+-----------------------------------------------------------------------------+
|                   EQUIPMENT GROUNDING CONDUCTOR (EGC) CORE MISSION           |
|                                                                             |
|   [NORMAL STATE]          ---> Carries ZERO continuous operating current     |
|   [FAULT CONDITION]       ---> Carries extreme fault current back to source  |
|   [SAFETY OBJECTIVE]      ---> 1. Keep non-current-carrying metal at 0V     |
|                                2. Create low-impedance path for fast OCPD trip|
|   [CODE GOVERNING RULES]  ---> NEC 250.4(A)(3), 250.118, 250.122            |
+-----------------------------------------------------------------------------+

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1. Types of Equipment Grounding Conductors (NEC 250.118)

Under NEC 250.118, an equipment grounding conductor can take the form of an insulated wire, a bare wire, or specific metallic raceway and cable armor systems listed as suitable for grounding.

+-----------------------------------------------------------------------------+
|                      NEC 250.118 RECOGNIZED EGC TYPES                       |
|                                                                             |
|   [WIRE-TYPE CONDUCTORS]                                                    |
|   - 250.118(1): Copper, aluminum, or copper-clad aluminum conductor         |
|                 (Insulated, covered, or bare; solid or stranded)            |
|                                                                             |
|   [RIGID METALLIC RACEWAYS - NO WIRE REQUIRED IF LISTED FITTINGS USED]       |
|   - 250.118(2): Rigid Metal Conduit (RMC - Art. 344)                         |
|   - 250.118(3): Intermediate Metal Conduit (IMC - Art. 342)                  |
|   - 250.118(4): Electrical Metallic Tubing (EMT - Art. 358)                  |
|                                                                             |
|   [FLEXIBLE RACEWAYS - STRICT LIMITATIONS APPLY (6 FT / 20A RULE)]          |
|   - 250.118(5): Flexible Metal Conduit (FMC - Art. 348)                      |
|   - 250.118(6): Liquidtight Flexible Metal Conduit (LFMC - Art. 350)         |
|   - 250.118(7): Flexible Metallic Tubing (FMT - Art. 360)                    |
|                                                                             |
|   [CABLE ARMOR & ASSEMBLIES]                                                |
|   - 250.118(8): Armor of Type AC Cable (Art. 320) with internal bonding tape |
|   - 250.118(10): Listed Type MC Cable with interlocked armor & bonding tape |
|   - 250.118(11): Metallic Cable Trays (Art. 392) complying with 392.60       |
|   - 250.118(12): Cablebus framework (Art. 370)                              |
|   - 250.118(13): Listed metal-enclosed busway (Art. 368)                    |
|   - 250.118(14): Surface metal raceways listed for grounding (Art. 386)     |
+-----------------------------------------------------------------------------+

The 6-Foot Flexible Conduit Rule (FMC and LFMC)

One of the most frequently tested topics on the Idaho Journeyman exam is the strict limitation on using Flexible Metal Conduit (FMC) or Liquidtight Flexible Metal Conduit (LFMC) as the sole EGC without pulling a separate wire EGC inside.

Under NEC 250.118(5) and 250.118(6), FMC and LFMC are permitted as the sole equipment grounding path only if ALL four (4) of the following conditions are met:

1. Fittings: The conduit is terminated in fittings listed for grounding.
2. Trade Size: The trade size does not exceed Trade Size 1-1/4 (metric designator 35) (Trade sizes 1/2 in. through 1-1/4 in.). Trade size 3/8 in. is permitted for fixture whips under 348.20(A).
3. Maximum Length: The total combined length of the flexible conduit in the ground-fault current path does not exceed 1.8 m (6 ft).
4. Overcurrent Protection: The circuit conductors contained in the conduit are protected by an overcurrent protective device rated at 20 amperes or less for FMC (or 20A or less for 3/8" to 1/2" LFMC, and 60A or less for 3/4" to 1-1/4" LFMC).
5. Flexibility: The installation is not installed to provide flexibility after installation (e.g., vibrating motors or movable machinery always require a separate wire-type EGC or external bonding jumper regardless of length).

+-----------------------------------------------------------------------------+
|                 FMC / LFMC AS GROUNDING CONDUCTOR CHECKLIST                 |
|                                                                             |
|   [CRITERIA]                    | [PASS CONDITION]     | [FAIL CONDITION]   |
|   ------------------------------+----------------------+------------------- |
|   Conduit Length                | <= 6 Feet (1.8 m)    | > 6 Feet           |
|   Conduit Trade Size            | 1/2" to 1-1/4"       | 1-1/2" or larger   |
|   Circuit Breaker / Fuse Rating | <= 20 Amperes        | >= 25 Amperes      |
|   Vibration / Machine Movement  | Stationary only      | Provides movement  |
|                                                                             |
|   >>> IF ANY CONDITION FAILS: A SEPARATE WIRE EGC IS MANDATORY!             |
+-----------------------------------------------------------------------------+

Type MC Cable Armor as an EGC (NEC 250.118(10))

Not all Type MC (Metal-Clad) cable armor qualifies as an EGC:

• Standard Interlocked Armor MC: Standard aluminum or steel interlocked armor alone is not an EGC. It requires an internal green or bare wire-type EGC.
• All-in-One / Smart Armor MC (MCI-A): Features an aluminum interlocked armor combined with an internal bare full-sized aluminum bonding strip in continuous contact with the armor. The combination of the sheath and bonding strip is listed as an equipment grounding conductor under NEC 250.118(10)(a).
• Smooth or Corrugated Metallic Tube MC: Listed as an EGC under 250.118(10)(b).

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2. Equipment Grounding Conductor Identification (NEC 250.119)

Under NEC 250.119, conductors used as equipment grounding conductors must be clearly distinguished from ungrounded phase conductors and grounded neutral conductors.

+-----------------------------------------------------------------------------+
|                       EGC IDENTIFICATION PROTOCOLS                          |
|                                                                             |
|   [CONDUCTORS 6 AWG AND SMALLER]                                            |
|   * Must have a continuous green outer finish, OR                           |
|   * Continuous green outer finish with one or more yellow stripes, OR       |
|   * Be completely bare.                                                     |
|   * CRITICAL EXAM RULE: Tape or paint re-identification is PROHIBITED       |
|     on conductors 6 AWG and smaller in field raceway installations!         |
|                                                                             |
|   [CONDUCTORS 4 AWG AND LARGER]                                            |
|   * Permitted to be permanently re-identified at each termination and      |
|     pull point at the time of installation.                                 |
|   * Permitted methods:                                                      |
|     1. Green tape encircling the conductor.                                 |
|     2. Stripping insulation from the entire exposed length.                 |
|     3. Permanent green marking or paint.                                    |
+-----------------------------------------------------------------------------+

[!WARNING] Field Exam Trap — Conductor Re-Identification: Electricians cannot pull a black #10 AWG or #8 AWG wire through conduit and wrap green tape around the ends to make it an EGC. The NEC strictly forbids field re-identification of conductors 6 AWG or smaller as EGCs (NEC 250.119). Re-identification with green tape is only permitted for conductors 4 AWG and larger.

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3. Sizing Wire-Type EGCs (NEC Table 250.122)

Wire-type equipment grounding conductors for branch circuits and feeders are sized from NEC Table 250.122 based on the rating or setting of the upstream fuse or circuit breaker protecting the conductors.

+-----------------------------------------------------------------------------+
|                 NEC TABLE 250.122 MASTER SIZING LOOKUP TABLE                |
|                                                                             |
|   RATING OR SETTING OF AUTOMATIC    |  MINIMUM SIZE EQUIPMENT GROUNDING     |
|   OVERCURRENT DEVICE (AMPERES)      |  CONDUCTOR (AWG OR KCMIL)             |
|   NOT EXCEEDING:                    |  COPPER WIRE       |  ALUMINUM WIRE   |
|   ==================================+====================+==================|
|                15 A                 |      14 AWG        |      12 AWG      |
|                20 A                 |      12 AWG        |      10 AWG      |
|                30 A                 |      10 AWG        |       8 AWG      |
|                40 A                 |      10 AWG        |       8 AWG      |
|                60 A                 |      10 AWG        |       8 AWG      |
|               100 A                 |       8 AWG        |       6 AWG      |
|               200 A                 |       6 AWG        |       4 AWG      |
|               300 A                 |       4 AWG        |       2 AWG      |
|               400 A                 |       3 AWG        |       1 AWG      |
|               500 A                 |       2 AWG        |     1/0 AWG      |
|               600 A                 |       1 AWG        |     2/0 AWG      |
|               800 A                 |     1/0 AWG        |     3/0 AWG      |
|              1000 A                 |     2/0 AWG        |     4/0 AWG      |
|              1200 A                 |     3/0 AWG        |   250 kcmil      |
|              1600 A                 |     4/0 AWG        |   350 kcmil      |
|              2000 A                 |   250 kcmil        |   400 kcmil      |
|              2500 A                 |   350 kcmil        |   600 kcmil      |
|              3000 A                 |   400 kcmil        |   600 kcmil      |
|              4000 A                 |   500 kcmil        |   800 kcmil      |
|              5000 A                 |   700 kcmil        |  1200 kcmil      |
|              6000 A                 |   800 kcmil        |  1200 kcmil      |
+-----------------------------------------------------------------------------+

General Principles for Table 250.122 Application

1. OCPD Governs: EGC size depends strictly on the upstream OCPD rating, not the ampacity of the phase conductors. For example, a 60A circuit breaker protecting #4 AWG conductors requires only a #10 AWG Copper EGC.
2. EGC Never Required to Exceed Phase Conductors (250.122(A)): An equipment grounding conductor is never required to be larger than the ungrounded circuit conductors supplying the equipment.
3. Multiple Circuits in a Single Raceway (250.122(C)): Where a single EGC is run in a raceway containing multiple circuits, the EGC is sized based on the largest overcurrent device protecting any circuit in that raceway.

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4. Mandatory Proportional Adjustment for Conductor Upsizing (NEC 250.122(B))

When ungrounded phase conductors are increased in size—most commonly to mitigate voltage drop over long circuit lengths—the equipment grounding conductor must be proportionally increased in size according to circular mil area.

Why Proportional Upsizing is Required

When phase conductors are upsized, the impedance of the phase conductor drops. If a ground fault occurs at the end of a long run and the EGC remains small, the EGC represents a disproportionately high resistance, limiting fault current and preventing fast magnetic trip operation of the breaker. Upsizing the EGC proportionally restores low total circuit loop impedance.

+-----------------------------------------------------------------------------+
|               NEC 250.122(B) PROPORTIONAL UPSIZING FORMULA                  |
|                                                                             |
|   EGC_new (cmil) = EGC_table (cmil) x [ Phase_actual (cmil) / Phase_min (cmil) ]
|                                                                             |
|   Where:                                                                    |
|   - EGC_table = Circular mil area of standard EGC from Table 250.122        |
|   - Phase_actual = Circular mil area of the upsized phase conductor         |
|   - Phase_min = Minimum circular mil area required for circuit ampacity     |
|                 (from Table 310.16 at conductor terminal temperature rating)|
+-----------------------------------------------------------------------------+

Master Conductor Properties Lookup (Chapter 9, Table 8)

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5. Step-by-Step Worked Math Examples: 250.122(B) Upsizing

Worked Example 1: 50-Ampere Circuit Upsized for Voltage Drop

Scenario: A 50-ampere, 240V single-phase circuit supplies an outbuilding located 300 feet away. The minimum phase conductor size for a 50A circuit is #8 AWG THHN Copper (50A @ 75°C). To limit voltage drop to under 3%, the phase conductors are upsized to #2 AWG Copper. Determine the required size of the copper equipment grounding conductor.

Step 1: Determine Minimum Required Phase Conductor and Baseline EGC
- Minimum Phase Conductor for 50A = #8 AWG Copper
- Area of #8 AWG Copper (Ch. 9, Table 8) = 16,510 cmil
- Baseline EGC for 50A OCPD (Table 250.122) = #10 AWG Copper
- Area of #10 AWG Copper (Ch. 9, Table 8) = 10,380 cmil

Step 2: Determine Area of Actual Upsized Phase Conductor
- Actual Upsized Phase Conductor = #2 AWG Copper
- Area of #2 AWG Copper (Ch. 9, Table 8) = 66,360 cmil

Step 3: Calculate the Upsizing Proportional Ratio (Multiplier)
- Multiplier = Phase_actual / Phase_min
- Multiplier = 66,360 cmil / 16,510 cmil = 4.01938

Step 4: Compute Required Minimum Circular Mil Area for New EGC
- EGC_new = EGC_table x Multiplier
- EGC_new = 10,380 cmil x 4.01938 = 41,721.2 cmil

Step 5: Select Conductor from Chapter 9, Table 8
- Comparing 41,721.2 cmil to Table 8:
  * #6 AWG = 26,240 cmil (Too small)
  * #4 AWG = 41,740 cmil (41,740 >= 41,721.2 - Complies!)

Final Answer: The equipment grounding conductor must be upsized to #4 AWG Copper.

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Worked Example 2: 100-Ampere Feeder Upsized to 2/0 AWG

Scenario: A 100-ampere feeder with 75°C terminals normally requires #3 AWG Copper (85A @ 75°C is insufficient, so #3 AWG rated at 85A with 240.4(B) or #3 rated 100A at 90°C basis / #3 AWG is 52,620 cmil; standard minimum 100A conductor is #3 AWG Cu). The feeder is upsized to 2/0 AWG Copper due to distance. Determine the minimum copper EGC size.

Step 1: Identify Parameters from Tables
- Minimum Phase Conductor = #3 AWG Cu = 52,620 cmil
- Actual Upsized Phase Conductor = 2/0 AWG Cu = 133,100 cmil
- Table 250.122 Baseline EGC for 100A = #8 AWG Cu = 16,510 cmil

Step 2: Calculate Proportional Multiplier
- Multiplier = 133,100 cmil / 52,620 cmil = 2.52945

Step 3: Calculate New Required EGC Area
- EGC_new = 16,510 cmil x 2.52945 = 41,761.3 cmil

Step 4: Select Conductor from Chapter 9, Table 8
- Comparing 41,761.3 cmil to Table 8:
  * #4 AWG = 41,740 cmil (Slightly smaller than 41,761.3 cmil)
  * #3 AWG = 52,620 cmil (Exceeds required area)

Final Answer: The equipment grounding conductor must be upsized to #3 AWG Copper.

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6. EGCs in Parallel Raceways and Multiconductor Cables (NEC 250.122(F))

When circuit conductors are run in parallel in multiple raceways or multi-conductor cables under NEC 310.10(G), the sizing of the equipment grounding conductor is subject to strict rules under NEC 250.122(F).

+-----------------------------------------------------------------------------+
|                 PARALLEL RACEWAY EGC SIZING MANDATE (250.122(F))             |
|                                                                             |
|   [RULE: FULL-SIZED EGC IN EACH RACEWAY]                                    |
|   * Each raceway or cable MUST contain a FULL-SIZED equipment grounding     |
|     conductor sized for the COMPLETE circuit overcurrent protective device  |
|     from Table 250.122.                                                     |
|   * YOU CANNOT DIVIDE THE EGC SIZE BY THE NUMBER OF PARALLEL CONDUITS!      |
|                                                                             |
|   [EXAMPLE: 800-AMPERE FEEDER IN TWO (2) PARALLEL CONDUITS]                 |
|   - Total OCPD Rating = 800 Amperes                                         |
|   - Table 250.122 EGC for 800A = 1/0 AWG Copper                             |
|                                                                             |
|   * Raceway #1 Contents: 3 x 500 kcmil Phase + 1 x 1/0 AWG Copper EGC       |
|   * Raceway #2 Contents: 3 x 500 kcmil Phase + 1 x 1/0 AWG Copper EGC       |
|                                                                             |
|   >>> (Installing a #4 AWG or splitting the 1/0 AWG is a severe violation!) |
+-----------------------------------------------------------------------------+

Why Each Parallel Conduit Requires a Full-Sized EGC

If a ground fault occurs inside one raceway (e.g., Phase A faults to Conduit 1), that individual conduit's EGC must carry the entire 800-ampere fault current back to the panel to trip the 800A breaker. If the EGC were divided in half, the undersized grounding conductor would fuse and burn open before the 800A breaker could clear the fault.

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7. Exam Traps & Key Takeaways Checklist

• EGC vs. GEC Sizing Tables: Always use Table 250.122 for Equipment Grounding Conductors (based on OCPD size). Use Table 250.66 for Grounding Electrode Conductors (based on phase wire size). Never confuse the two!
• Smallest EGC: The smallest standard copper EGC for branch circuits is #14 AWG (15A circuit). Under Table 250.122, a 30A, 40A, or 60A circuit breaker all require a #10 AWG Copper EGC.
• Flexible Conduit Limits: Remember the numbers 6 ft, 20A, and 1-1/4 in. for FMC/LFMC as an EGC without a wire.
• Proportional Upsizing: Whenever phase conductors are upsized for voltage drop, the EGC must be proportionally upsized in circular mil area under 250.122(B).