9.1 Equipment Grounding Conductors

Why the EGC Matters on the TX Journeyman Exam

Equipment grounding is a Knowledge-part staple. PSI draws items straight from NEC 250 Parts V and VI — type recognition, identification, and Table 250.122 lookups. A common trap is confusing the equipment grounding conductor (the EGC, sized from Table 250.122) with the grounding electrode conductor (GEC, sized from Table 250.66, covered in Chapter 4). They are two different conductors with two different tables and two different jobs. The EGC does not connect to the earth; it connects the faulted metal back to the system neutral at the service or source so the breaker trips.

Performance Requirements — NEC 250.4(A)(2) and (A)(3)

Article 250.4 states what grounding and bonding must accomplish, not just how to do it. For grounded systems:

• 250.4(A)(2) — Conductive materials enclosing electrical conductors or components, or that are likely to become energized, shall be grounded and bonded in a manner that creates an effective path for fault current.
• 250.4(A)(3) — Bonding of electrically conductive materials and other equipment shall be sufficient to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.
• 250.4(A)(5) — The impedance of the effective ground-fault current path shall be low enough to allow operation of the overcurrent protective device. This is the performance test — if the breaker will not trip, the path is not code-compliant, regardless of wire size.

Types of Equipment Grounding Conductors — NEC 250.118

NEC 250.118 lists the conductors and raceways permitted to serve as an EGC. The most-tested entries:

Exam trap: FMC, LFMC, and reduced-size flexible conduits are not a reliable EGC for most installations. A separate wire-type EGC must be pulled inside them. The 6 ft / 20 A exception is narrow and tested.

Identification — NEC 250.119

An insulated wire-type EGC must have a continuous green finish or green with one or more yellow stripes. The exceptions that show up on the exam:

• #6 AWG and larger — may be re-identified at each end and at every point where the conductor is accessible by stripping the insulation, or by colored tape, cable ties, or paint. The re-identification must encircle the conductor.
• Multiconductor varnished-cloth-insulated cables (legacy) — a green identifying marker is permitted at termination.
• A conductor with insulation that is green may not be used as a grounded (neutral) conductor, and a conductor that is white, gray, or has three continuous white stripes may not be used as an EGC.

Sizing the Wire-Type EGC — NEC 250.122 and Table 250.122

NEC 250.122(A) requires the EGC to be sized by Table 250.122 using the rating of the overcurrent protective device ahead of the conductors — not the ungrounded conductor ampacity. The EGC is never required to be larger than the ungrounded conductors.

Verified 2023 NEC Table 250.122 (copper, the common range):

For aluminum or copper-clad aluminum EGCs, Table 250.122 lists a separate (larger) column — use it when the question says aluminum.

Voltage Drop Adjustment — NEC 250.122(B)

When ungrounded conductors are increased in size for voltage drop, the EGC must be increased in size proportionally. The formula:

EGC size = Table 250.122 size × (adjusted ungrounded conductor area / Table-ampacity ungrounded conductor area)

Example: a 100 A feeder is wired in 2 AWG copper instead of the minimum 4 AWG copper to control voltage drop. From Table 250.122, the EGC is 8 AWG. From Chapter 9, Table 8 (conductor areas, stranded):

• 4 AWG stranded ≈ 41,740 cmil
• 2 AWG stranded ≈ 66,360 cmil

Ratio = 66,360 / 41,740 = 1.59. New EGC area = 8 AWG area (16,510 cmil) × 1.59 = 26,250 cmil → round up to 6 AWG (26,240 cmil). The EGC moves up one size.

Worked Examples

Example 1 — 60 A feeder. A 60 A feeder supplies a panelboard. Size the wire-type copper EGC.

• Step 1: Identify the OCPD rating = 60 A.
• Step 2: Table 250.122, copper column, 60 A row → 10 AWG copper.

The ungrounded conductors could be 6 AWG copper (THHN, 75 °C column = 65 A), but the EGC is driven by the OCPD rating, not the conductor size — still 10 AWG.

Example 2 — 200 A service. A 200 A service-entrance panel has a 200 A main breaker. Size the wire-type copper EGC run with the service-entrance conductors.

• Step 1: OCPD rating = 200 A.
• Step 2: Table 250.122, copper column, 200 A row → 6 AWG copper.

Note this is the equipment grounding conductor, not the grounding electrode conductor (GEC). The GEC for a 2/0 copper service-entrance conductor would be sized from Table 250.66 — 8 AWG copper — a separate calculation covered in Chapter 4. Mixing the two tables is the most common miss on this exam area.