5.1 Equipment Grounding Conductors (250.122)

5.1 Equipment Grounding Conductors (250.122)

Quick Answer: Size wire-type equipment grounding conductors from Table 250.122 using the ampere rating of the overcurrent device protecting the circuit. Do not treat EGC sizing like a Grounding Electrode Conductor under 250.66. If you enlarge the ungrounded conductors beyond the minimum needed for ampacity (voltage drop is the classic reason), enlarge the EGC proportionately under 250.122(B).

On the Arkansas Journeyman Electrician exam (Prov / ADLL, NEC 2023, 60 questions, 3 hours, 70% pass), Grounding and Bonding is 6 items. The second half of that outline—equipment grounding and bonding—turns on Article 250 Part VI and Part V continuity rules. Candidates who confuse Table 250.66 (GEC / service electrode conductor) with Table 250.122 (EGC) lose easy points. This section is only about equipment grounding conductors that provide the effective ground-fault current path for raceways and equipment on the load side of the service (and similarly on feeders and branch circuits).

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Grounding vs Bonding vs EGC (keep the vocabulary straight)

• Grounding connects a system or equipment to earth (or to a grounding electrode system that is earth-connected).
• Bonding connects metallic parts to each other so they are electrically continuous and can carry fault current safely.
• An equipment grounding conductor (EGC) is the conductive path that bonds normally non–current-carrying metal parts back toward the source so a ground fault can open the overcurrent device.

The EGC is not the grounded (neutral) conductor, and it is not the grounding electrode conductor. On Prov stems, if the question says “equipment grounding conductor” or “green/bare equipment ground,” you are in 250.122 territory.

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The master rule: size from the OCPD (250.122)

250.122(A) requires that EGCs of the wire type be sized not smaller than shown in Table 250.122, based on the rating or setting of the automatic overcurrent device in the circuit ahead of the equipment, raceway, cable tray, etc. Where the overcurrent device consists of instantaneous-trip circuit breakers or motor short-circuit protectors, the size is based on the maximum setting permitted for that device under the applicable Code sections.

Worked Table 250.122 examples (copper)

Open Table 250.122 in your NEC. Representative copper minima (verify every row in your book—do not invent sizes):

Example A — 20 A branch circuit: Copper EGC minimum = 12 AWG.

Example B — 100 A feeder: Copper EGC minimum = 8 AWG.

Example C — 200 A feeder: Copper EGC minimum = 6 AWG.

Example D — aluminum EGC: Use the aluminum/copper-clad aluminum column in the same table. A 100 A circuit commonly needs 6 AWG aluminum EGC (confirm in Table 250.122). Never mix columns.

The table also states that where the conductors are sized to compensate for voltage drop, 250.122(B) applies—Table 250.122 alone is only the starting minimum.

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Proportionate upsizing — 250.122(B)

If ungrounded conductors are increased in size from the minimum size that would be required for ampacity (for example, for voltage drop, ambient correction stacking that forced a larger wire, or design preference), EGCs of the wire type shall be increased in size proportionately to the circular-mil area of the ungrounded conductors.

Exam method:

1. Find the minimum ungrounded conductor size that ampacity would have allowed for that OCPD/load.
2. Find the actual ungrounded conductor size installed.
3. Compute the ratio of circular mils (actual ÷ minimum).
4. Multiply the Table 250.122 EGC circular mils by that ratio and round up to a standard size that meets or exceeds the product.

Illustration: A 100 A feeder would normally use 3 AWG copper ungrounded conductors for ampacity in the problem’s conditions, but the designer installs 1 AWG copper for voltage drop. Table 250.122 copper EGC for 100 A is 8 AWG. Upsize the EGC by the same circular-mil ratio (1 AWG ÷ 3 AWG cmil areas), then select the next standard EGC size that is not smaller than that product. On Prov, you may be asked for the concept (“must increase proportionately”) even when exact cmil arithmetic is not required.

Do not leave an 8 AWG EGC on a voltage-drop-upsized feeder just because Table 250.122 still says 8 for 100 A—250.122(B) overrides that complacency.

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Multiple circuits, motors, and parallel runs

250.122(C) Multiple Circuits. Where a single EGC is run with multiple circuits in the same raceway, cable, or cable tray, size it for the largest overcurrent device protecting conductors in that raceway/cable/tray.

250.122(D) Motor Circuits. Size the EGC from Table 250.122 based on the rating of the branch-circuit short-circuit and ground-fault protective device, not from motor full-load current alone. Instantaneous-trip devices use the maximum setting permitted for the installation as the table index.

250.122(F) Conductors in Parallel. Where circuit conductors are run in parallel in separate raceways or cables, an EGC must be installed in each parallel raceway or cable, and each EGC is sized from Table 250.122 based on the overcurrent device protecting the paralleled set (with the section’s special notes for wire-type EGCs in parallel). Do not “share one fat green” across multiple parallel conduits unless the Code text you open for that year expressly permits the arrangement you drew.

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Raceways as the EGC — 250.118

250.118 lists wiring methods permitted to serve as an equipment grounding conductor: rigid metal conduit, intermediate metal conduit, electrical metallic tubing (with fittings), flexible metal conduit and liquidtight flexible metal conduit under stated length/qualification limits, metal-clad cable armor under listed conditions, and others. When the raceway qualifies, a separate wire-type EGC is not always required—but if a wire-type EGC is installed, it must still satisfy 250.122.

On exam day, a stem that asks “minimum size equipment grounding conductor” almost always wants the wire-type Table 250.122 answer unless it expressly asks whether the raceway alone is acceptable.

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Common Prov traps

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Timed open-book tips

Tab Table 250.122, 250.122(B), and 250.118. Practice three lookups: 20 A, 100 A, and 400 A copper. Then practice one voltage-drop upsizing word problem until the proportionate rule is automatic. Pair this section with Chapter 4’s electrode/GEC material so you never open the wrong table under time pressure.