8.2 Equipment Grounding Conductors

Equipment Grounding Conductors

The Equipment Grounding Conductor (EGC) is the primary active line of defense against electrical shock and electrocution in premises wiring. While Grounding Electrode Conductors (GEC) connect electrical systems to the earth for voltage stabilization and lightning protection, EGCs connect equipment metal enclosures, raceways, junction boxes, and appliance chassis back to the system grounded conductor at the service or transformer. During normal operation, the EGC carries zero current and maintains all exposed metal at zero volts relative to ground. When an insulation breakdown occurs, the EGC acts as the low-impedance metallic superhighway carrying immense ground-fault current straight to the source, instantly tripping the circuit breaker or blowing the fuse. On the Kentucky Journeyman Electrician examination, questions involving NEC Table 250.122, proportional upsizing under NEC 250.122(B), and recognized wiring methods under NEC 250.118 are among the most frequent and calculation-intensive.

---

1. Definition and Purpose of the EGC (Article 100 & Article 250 Part VI)

Under NEC Article 100, the Equipment Grounding Conductor is defined as:

Equipment Grounding Conductor (EGC): A conductive path(s) that is part of an effective ground-fault current path and that connects normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

The Effective Ground-Fault Current Path (Article 100 & 250.4(A)(5))

To clear a fault, the complete circuit must satisfy the definition of an Effective Ground-Fault Current Path:

• It must be intentionally constructed, permanent, and electrically continuous.
• It must possess low impedance sufficient to facilitate the instantaneous operation of the overcurrent protective device (circuit breaker or fuse).
• It must have the ampacity to conduct safely the maximum fault current likely to be imposed upon it without melting, burning open, or igniting surrounding building materials.

+-----------------------------------------------------------------------------------+
|                    THE COMPLETE GROUND-FAULT CURRENT CIRCUIT                      |
|                                                                                   |
|  1. Phase Conductor contacts metal junction box or equipment enclosure.           |
|  2. Fault Current travels over the Equipment Grounding Conductor (EGC)            |
|     (wire conductor, EMT, RMC, or IMC).                                           |
|  3. Fault Current reaches the Panelboard Equipment Ground Bus.                    |
|  4. Fault Current crosses the Main Bonding Jumper (MBJ) at the service entrance.  |
|  5. Fault Current transfers to the Grounded Service Conductor (Neutral).          |
|  6. Fault Current returns to the Utility Distribution Transformer Secondary.       |
|  7. Circuit Loop Closed: Ultra-low impedance forces OCPD instantaneous trip!      |
+-----------------------------------------------------------------------------------+

---

2. Recognized Types of Equipment Grounding Conductors (NEC 250.118)

An EGC does not necessarily have to be a green insulated copper wire. NEC 250.118 recognizes fourteen specific types of equipment grounding conductors, categorized into wire conductors, metallic raceways, and metallic cable assemblies:

Comprehensive Breakdown of Permitted EGC Types (NEC 250.118(A))

Critical Exam Nuances for Flexible Conduits (FMC & LFMC)

Journeyman exam questions frequently test the strict limitations on using FMC and LFMC as the equipment grounding conductor:

1. The 6-Foot Length Limit: The total ground return path through the flexible conduit cannot exceed 6 feet (1.8 m). If you run 8 feet of FMC, you must install a separate wire-type EGC inside the conduit.
2. The 20A / 60A Overcurrent Limit: Standard FMC is permitted as an EGC only where the circuit is protected at 20 amperes or less. LFMC is limited to 20A for 3/8-inch and 1/2-inch trade sizes, and 60A for 3/4-inch through 1-1/4-inch trade sizes.
3. Flexibility After Installation: If the flexible conduit is installed to accommodate vibration or movement (such as connecting to an electric motor or vibrating compressor), a separate wire-type EGC must always be installed, regardless of conduit length or breaker rating.

---

3. Sizing EGCs Using NEC Table 250.122

When a wire-type equipment grounding conductor is installed, its size is determined exclusively from NEC Table 250.122 based on the rating or setting of the overcurrent protective device (circuit breaker or fuse) protecting the circuit ahead of the equipment.

NEC Table 250.122: Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment

Key Takeaway for Exam Candidates: Notice that for overcurrent devices rated 30A, 40A, and 60A, the copper EGC size is identical: 10 AWG copper. Similarly, a 100A breaker requires an 8 AWG copper EGC, a 200A breaker requires a 6 AWG copper EGC, and a 400A breaker requires a 3 AWG copper EGC.

The Upper Limit Rule (NEC 250.122(A))

NEC 250.122(A): In no case shall the equipment grounding conductor be required to be larger than the ungrounded circuit conductors supplying the equipment.

---

4. Proportional Upsizing for Voltage Drop (NEC 250.122(B))

One of the most challenging calculation questions on the Kentucky Journeyman exam involves NEC 250.122(B): increasing the size of equipment grounding conductors when circuit phase conductors are adjusted or increased in size.

Why Does the Code Mandate Proportional Upsizing?

When branch-circuit or feeder conductors are upsized to counteract voltage drop over long circuit runs (e.g., runs of 200 to 500 feet), the physical length of the circuit introduces significant electrical resistance ($R = \rho \frac{L}{A}$). If the ungrounded phase conductors are upsized to reduce resistance but the equipment grounding conductor is left at its minimum Table 250.122 size, the total fault circuit loop impedance may become too high. Under a line-to-ground fault, the reduced fault current might fail to reach the instantaneous trip threshold of the breaker, causing delayed tripping and hazardous overheating of the undersized EGC.

The Proportional Sizing Formula

NEC 250.122(B) mandates that where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation, the wire-type equipment grounding conductor(s) shall be increased in size proportionally according to the circular mil area of the ungrounded conductors:

$\text{Proportional Multiplier} = \frac{\text{Area of Increased Phase Conductor (cmil)}}{\text{Area of Minimum Required Phase Conductor (cmil)}}$

$\text{Required New EGC Area (cmil)} = \text{Standard Table 250.122 EGC Area (cmil)} \times \text{Proportional Multiplier}$

Reference Values from NEC Chapter 9, Table 8 (Conductor Properties)

Worked Example 1: Branch Circuit Voltage Drop Upsizing

Problem: A $120\text{ V}$, $20\text{ A}$ branch circuit supplying outdoor lighting located 250 feet away has an initial minimum required conductor size of 12 AWG copper (6,530 cmil). Due to voltage drop, the electrician increases the circuit conductors to 8 AWG copper (16,510 cmil). What is the minimum size required for the copper equipment grounding conductor?

1. Identify minimum required phase conductor area: $12\text{ AWG} = 6{,}530\text{ cmil}$.
2. Identify upsized phase conductor area: $8\text{ AWG} = 16{,}510\text{ cmil}$.
3. Calculate the proportional multiplier: $\text{Multiplier} = \frac{16{,}510\text{ cmil}}{6{,}530\text{ cmil}} \approx 2.5283$
4. Identify base EGC size from Table 250.122 for a 20A breaker: 12 AWG copper (6,530 cmil).
5. Calculate required new EGC circular mil area: $\text{New EGC cmil} = 6{,}530\text{ cmil} \times 2.5283 = 16{,}510\text{ cmil}$
6. Lookup conductor size in Chapter 9, Table 8: $16{,}510\text{ cmil}$ corresponds exactly to 8 AWG copper.

• Answer: The EGC must be upsized to 8 AWG copper.

Worked Example 2: Feeder Circuit Proportional Upsizing

Problem: A 100-ampere feeder is supplied by an overcurrent device rated at 100A. The minimum conductor required for the load is 3 AWG THHN copper (52,620 cmil). To mitigate voltage drop over a 400-foot run, the phase conductors are increased to 1/0 AWG copper (105,600 cmil). What size copper EGC is required?

1. Minimum phase conductor area: $3\text{ AWG} = 52{,}620\text{ cmil}$.
2. Upsized phase conductor area: $1/0\text{ AWG} = 105{,}600\text{ cmil}$.
3. Calculate proportional multiplier: $\text{Multiplier} = \frac{105{,}600\text{ cmil}}{52{,}620\text{ cmil}} \approx 2.0068$
4. Base EGC size from Table 250.122 for a 100A OCPD: 8 AWG copper (16,510 cmil).
5. Calculate required new EGC circular mil area: $\text{New EGC cmil} = 16{,}510\text{ cmil} \times 2.0068 = 33{,}132\text{ cmil}$
6. Lookup conductor size in Chapter 9, Table 8:
   • 6 AWG is 26,240 cmil (less than 33,132 cmil — TOO SMALL!)
   • 4 AWG is 41,740 cmil (greater than 33,132 cmil — ADEQUATE!)

• Answer: The copper equipment grounding conductor must be upsized to 4 AWG copper.

---

5. Multiple Circuits in a Single Raceway (NEC 250.122(C))

In commercial and industrial wiring, multiple branch circuits or feeders are frequently pulled through a common raceway, cable tray, or trench.

• General Rule (NEC 250.122(C)): Where a single equipment grounding conductor is run in a raceway, cable, or cable tray with multiple circuits, it is permitted to install a single common equipment grounding conductor.
• Sizing Requirement: The single common EGC must be sized for the largest overcurrent device protecting any circuit conductors in that raceway.

+-----------------------------------------------------------------------------------+
|             MULTIPLE CIRCUITS IN A SINGLE RACEWAY (NEC 250.122(C))                |
|                                                                                   |
|  CONDUIT RUN CONTAINING THREE CIRCUITS:                                           |
|  +-----------------------------------------------------------------------------+  |
|  | Circuit 1: 120V, 20A Lighting Circuit (Phase + Neutral)                     |  |
|  | Circuit 2: 240V, 30A Water Heater Circuit (2 Hots)                          |  |
|  | Circuit 3: 208V, 60A Kitchen Appliance Feeder (3 Hots + Neutral)            |  |
|  |                                                                             |  |
|  | [ SINGLE COMMON EQUIPMENT GROUNDING CONDUCTOR ]                             |  |
|  | Sized for the LARGEST OCPD in the conduit: 60A Breaker                     |  |
|  | From Table 250.122: Minimum EGC = 10 AWG Copper                             |  |
|  +-----------------------------------------------------------------------------+  |
+-----------------------------------------------------------------------------------+

Example: A conduit contains a 20A branch circuit, a 40A branch circuit, and a 100A subfeeder. Instead of pulling three individual ground wires, the electrician may pull a single common copper EGC sized for the 100A breaker, which from Table 250.122 is an 8 AWG copper conductor.

---

6. Parallel Conductors (NEC 250.122(F))

When feeder or branch-circuit conductors are run in parallel in multiple raceways, a wire-type equipment grounding conductor, where used, must be installed in each raceway. Each one is sized from Table 250.122 using the rating of the overcurrent device that protects the whole feeder or branch circuit, not a share of it. Where parallel conductors share a single raceway or cable tray, one wire-type EGC sized the same way is enough.

Example: A 600-ampere feeder runs as two parallel sets in two conduits. Table 250.122 lists 1 AWG copper for a 600-ampere device, so each conduit gets a 1 AWG copper EGC. Sizing each EGC for 300 amperes (4 AWG) is a common mistake. If the ungrounded conductors were also upsized for voltage drop, 250.122(B) increases each EGC in proportion.

7. Identification of Equipment Grounding Conductors (NEC 250.119)

NEC 250.119 governs the color coding and identification of wire-type equipment grounding conductors:

1. Conductors 6 AWG and Smaller: Unless bare, equipment grounding conductors 6 AWG and smaller must have a continuous outer finish that is green or green with one or more yellow stripes.
   • PROHIBITION: You are not permitted to pull a white, black, or red wire sized 6 AWG or smaller and re-identify it with green phase tape in the field! The insulation must be factory-colored green.
2. Conductors Larger than 6 AWG (4 AWG and Larger): Permitted to be permanently identified as an EGC at the time of installation at every point where the conductor is accessible (e.g., junction boxes, pull boxes, panelboards) by one of the following methods:
   • Stripping the insulation from the entire exposed length.
   • Coloring the exposed insulation green (using green paint or dye).
   • Marking the exposed insulation with green phase tape or green adhesive labels encircling the conductor.