15.4 Panelboards (Art 408)

Panelboards in the Utilization Outline

Prov lists Utilization and General Use Equipment as its own subject area (6 items). Article 408 panelboard questions sit beside luminaires and appliances because a panelboard is general-use distribution equipment — not a “service-only” topic. Service disconnect identity still lives in Article 230; once you are inside a panelboard, open 408.

Arkansas JW candidates should be fluent with directories, panelboard OCPD rules, phase arrangement, and grounding terminations. Working clearances remain 110.26 (Chapter 19), but many stems blend both articles.

Tab 408.3, 408.4, 408.36, 408.40, and 408.54.

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What Is a Panelboard?

Article 100 defines a panelboard as a single panel or group of panel units designed for assembly in a single enclosure, including buses and automatic overcurrent devices, with or without switches for control of light, heat, or power circuits, designed to be placed in a cabinet or cutout box. Contrast with a switchboard (typically freestanding, larger) and a switchgear assembly. Exam language that says “loadcenter” or “breaker panel” is almost always a panelboard under 408.

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Circuit Directory and Identification — 408.4

408.4(A) requires every circuit and circuit modification to be legibly identified as to its clear, evident, and specific purpose or use. The identification must be included in a circuit directory located on the face or inside of the panel door (or equivalent approved location). Directory entries must not rely on temporary conditions (“John’s room”) when a permanent description is possible (“Bedroom 2 receptacles”). Spare and unused breakers should be identified as such.

408.4(B) addresses source identification for certain equipment — panelboards supplied by more than one power source need durable markings identifying the sources. On exam day, a stem showing a generator backfeed or dual supply without source labels is an identification failure under 408 / related articles.

Exam trap: A neat panel with breakers labeled only “lights” and “plugs” for an entire dwelling floor often fails the “specific purpose” standard.

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Overcurrent Protection of Panelboards — 408.36

408.36 requires each panelboard to be protected by an overcurrent protective device with a rating not greater than the panelboard rating. Protection may be located within or ahead of the panelboard, subject to the section’s details and exceptions (including certain tap rules and individual protection pathways).

Historically, “lighting and appliance branch-circuit panelboards” had distinctive rules; the modern Code text still distinguishes panelboard types and locations. For journeyman purposes:

• The panelboard ampere rating is a hard ceiling for the upstream OCPD (unless a specific exception applies).
• Installing a 200 A panelboard on a 225 A main breaker without an allowed exception is a rating violation.
• Backfed devices used as main protection must be secured with additional fastener hardware where required by the listing / 408.36 related rules.

408.30 and surrounding text address use and installation; combine with conductor ampacity and termination temperature rules from Articles 110 and 310 when sizing feeders to panels.

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Bus Arrangement, High Leg, and Number of Devices

408.3 covers support, arrangement, and barriers. Phase arrangement on 3-phase buses is typically A-B-C from front to back, top to bottom, or left to right as viewed from the front. On a 4-wire delta with a high leg, the high leg (higher voltage to ground) must be identified — commonly orange — and positioned per 408.3(E)/(F) (often the “B” phase in the panel). Mislanding the high leg on a 120 V breaker is a classic damage scenario and a classic exam warning.

408.54 limits a panelboard to not more than 42 overcurrent devices (and related counting rules historically associated with lighting/appliance panelboards — verify the exact 2023 wording and exceptions in your book). Class CTL and similar listing constraints also limit stab configurations — follow the panelboard’s listing (110.3(B)).

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Grounding and Bonding at Panelboards — 408.40

408.40 requires panelboard cabinets and frames to be connected to an equipment grounding conductor. Equipment grounding conductors must terminate on a terminal bar secured inside the cabinet. Neutral (grounded conductor) terminal bars are isolated from the enclosure on separately derived and downstream panelboards where bonding jumpers are not permitted — neutrals and grounds are bonded together only at the service disconnect / SDS bonding location per Article 250.

Exam hinge: In a subpanel, landing equipment grounding conductors on the neutral bar (or bonding the neutral bar to the can) creates objectionable parallel neutral current paths and fails 250/408 rules. Keep EGCs on the grounding bar bonded to the enclosure; keep neutrals on an insulated neutral bar.

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Installation Conditions That Show Up on Prov

Panelboards in wet or damp locations need suitable enclosures. Outdoor meter-main and combination service equipment may be both Article 230 service equipment and panelboard — answer with the article the stem targets.

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Practical Open-Book Drill

1. Read the stem: directory, high leg, subpanel bonding, or main OCPD vs. panel rating?
2. Open 408 for panel-specific rules; open 250 only for bonding/neutral separation; open 110.26 for clearances.
3. Check listing marks and ampere rating on the panelboard nameplate against the feeder OCPD.

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Arkansas Prov Takeaway

Utilization panelboard items reward precise 408.4 directories, 408.36 protection not exceeding the panel rating, correct high-leg identification, and clean subpanel neutral/ground separation. Use the 3-hour open-book window to confirm section numbers rather than relying on apprenticeship memory alone.