5.3 Panelboards & Switchboards (0403)
Key Takeaways
- NEC 408.4(A) requires every panelboard circuit to be legibly identified as to its clear, evident, and specific purpose on a durable circuit directory located at the panel.
- Overcurrent devices, including panelboards containing them, must not be located in bathrooms of dwelling units, dormitory units, or guest rooms (240.24(E)) or over the steps of a stairway (240.24(F)).
- The former 42-circuit limit on lighting and appliance panelboards was deleted in the 2008 NEC; a modern panelboard is bounded by its bus rating and available spaces instead.
- 230.71(B) still limits a service to six disconnects, but since the 2020 NEC they must be in separate enclosures, separate panelboards, barriered switchboard sections, or separate switchgear compartments — not six handles in one can.
- Panelboards must be protected by an overcurrent device rated not more than the panelboard rating (408.36), and industrial control panels under Article 409 must be marked with a short-circuit current rating that equals or exceeds the available fault current.
Panelboards & Switchboards (NEC Articles 408 and 409)
Quick Answer: Article 408 governs switchboards, switchgear, and panelboards — covering arrangement, identification, overcurrent protection, and construction. Key inspector items are the circuit directory (408.4(A)), the ban on bathrooms and stairways (240.24(E) and (F)), working clearances (110.26), dedicated equipment space (110.26(E)), and the overcurrent protection of the panelboard itself (408.36). Article 409 covers industrial control panels, with marking and short-circuit current rating (SCCR) requirements.
Panelboard vs Switchboard — 408.2
- Panelboard — a single panel or group of panel units assembled into a single enclosure, including buses and overcurrent devices, designed to control light, heat, or power circuits, and placed in a cabinet or cutout box accessible only from the front.
- Switchboard — a large single panel, frame, or assembly of panels with switches, overcurrent devices, buses, and instruments mounted on the face, back, or both; generally accessible from the rear as well as the front and not intended to be installed in a cabinet.
- Switchgear — an assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows), containing primary power circuit switching or interrupting devices with barriers between compartments.
All three definitions now live in Article 100, which the 2023 NEC consolidated.
Circuit Identification — 408.4 and 408.41
408.4(A) requires every circuit and circuit modification to be legibly identified as to its clear, evident, and specific purpose, on a circuit directory located on the face or inside the panel door (or at each switch or circuit breaker on a switchboard or switchgear). The identification must be sufficiently durable to withstand the environment, and "spare" is only acceptable for a genuinely unused space. 408.4(B) requires a field-applied label identifying the source that supplies the panelboard. Two related rules the exam pairs with this: 408.41 requires each grounded conductor to terminate in an individual terminal that is not also used for another conductor (so no doubled neutrals on one screw), and the simultaneous-disconnect requirement for multiwire branch circuits comes from 210.4(B), not Article 408.
Panelboard Location — Do's and Don'ts
| Permitted | Prohibited / restricted | Section |
|---|---|---|
| Dedicated spaces, utility rooms, electrical rooms | Bathrooms of dwelling units, dormitory units, and guest rooms/suites | 240.24(E) |
| Surface or recessed in finished walls | Over the steps of a stairway | 240.24(F) |
| Adjacent to the service entrance | In the vicinity of easily ignitible material, such as a clothes closet | 240.24(D) |
| Near the equipment it controls | Anywhere the 110.26 working space cannot be maintained | 110.26 |
| Dry locations | Damp or wet locations unless the enclosure is identified for the condition | 408.16, 312.2 |
Note the citation: the bathroom prohibition is 240.24(E), not a section of Article 408 — 408.17 is titled Location Relative to Easily Ignitible Material.
Overcurrent Protection — 408.36
408.36 requires each panelboard to be protected by an overcurrent device having a rating not greater than that of the panelboard, located within or at any point on the supply side of the panelboard. Exceptions cover individual protection for panelboards used as service equipment on certain existing installations, panelboards protected by two main devices whose combined rating does not exceed the panelboard rating, and panelboards supplied through a transformer where the protection is on the primary side under stated conditions. The legacy 42-circuit rule (former 408.35) was deleted in the 2008 NEC; a modern panelboard is bounded by its bus rating and the number of spaces the manufacturer provides, not by a fixed circuit count.
Panelboard Construction and Short-Circuit Rating — 408.6
408.6 requires the short-circuit current rating (SCCR) of a switchboard, switchgear, or panelboard to be field marked and to be not less than the available fault current, and the equipment may not be installed where the available fault current exceeds that rating. Where a panelboard is supplied through a transformer, the transformer impedance and the supply conductors determine the available fault current at the panelboard. Two companion rules: 110.24 requires service equipment other than at dwelling units to be field marked with the maximum available fault current and the date of the calculation, and 230.66 requires service equipment to be listed or field labeled as suitable for use as service equipment (which is a marking requirement, not an SCCR requirement — a distinction the exam likes).
Working Clearances & Dedicated Space
- 110.26(A)(1) — depth of working space is read from the table by voltage to ground and Condition 1, 2, or 3: at 0–150 V it is 3 ft for all three conditions; at 151–600 V it is 3 ft / 3½ ft / 4 ft; at 601–1000 V it is 3 ft / 4 ft / 5 ft. 110.26(A)(2) — the width is the width of the equipment or 30 in. (762 mm), whichever is greater, and the space must allow at least a 90-degree opening of equipment doors or hinged panels.
- 110.26(E) — dedicated equipment space: the floor-to-ceiling space equal to the footprint of the equipment is reserved for electrical equipment only, extending 6 ft above or to the structural ceiling.
- 240.24(A) — overcurrent devices shall be readily accessible, not more than 6 ft 7 in (2.0 m) above floor or working platform, and not located over stairs.
Panelboards as Service Equipment vs Distribution
When a panelboard is used as service equipment, the main bonding jumper and grounding electrode conductor connections must meet 250.28 and 250.24; the neutral is bonded to the enclosure. When used as a distribution panel downstream, the neutral is isolated from the enclosure. 408.3 covers panelboard construction including bus bar arrangement and the separation of neutrals and equipment grounds in distribution panels.
Switchboards — 408.10
408.16 requires switchboards, switchgear, and panelboards in damp or wet locations to be installed to comply with 312.2 — enclosures weatherproof, with 1/4 in. airspace behind where mounted on a masonry or similar surface. 408.17 requires them not to be located in the vicinity of easily ignitible material. 408.18(A) requires a space of not less than 3 ft (900 mm) between the top of a non-totally-enclosed switchboard or switchgear and any combustible ceiling, unless a noncombustible shield is provided; 408.18(B) simply directs the surrounding clearances to 110.26. There is no separate "3 ft at the rear" rule in Article 408 — rear working space, where rear access is required, comes from 110.26 as well. Panelboard enclosures must be dead front (408.38), so that no live parts are exposed to the operator.
Maximum Number of Disconnects — 230.71
Where a panelboard or switchboard serves as the service equipment, 230.71(B) still limits the service disconnecting means to two to six disconnects — but the 2020 NEC deleted the long-standing permission to mount them in a single enclosure. Under the current rule they must be a combination of separate enclosures each with a main, panelboards each with a main in the panelboard enclosure, switchboard vertical sections with barriers and one disconnect per section, or switchgear/metering-center compartments with one disconnect per compartment. The disconnects must be grouped (230.72(A)) and each marked to identify it as a service disconnect (230.70(B)). For multiple-occupancy buildings, 230.72(C) requires each occupant to have access to the disconnect supplying that occupancy, or the disconnects to be accessible only to building management under continuous supervision.
Industrial Control Panels — Article 409
Article 409 covers industrial control panels intended for general use and operating at 1000 volts or less. 409.110 requires marking with the manufacturer, supply voltage/phase/frequency, full-load current, and the short-circuit current rating of the panel; 409.22 prohibits installing the panel where the available fault current exceeds that SCCR. The 110.26 working clearances apply the same way they do to a panelboard.
Inspector Focus
Verify: (1) the circuit directory is complete, specific, and durable, and the source label required by 408.4(B) is present; (2) the panelboard is not in a prohibited bathroom, not over stair steps, and not near easily ignitible material; (3) working clearances and dedicated equipment space meet 110.26; (4) the overcurrent device protecting the panelboard does not exceed its rating (408.36); (5) each grounded conductor lands on its own terminal (408.41); (6) neutrals are bonded at the service and isolated at every downstream panel; and (7) the marked SCCR equals or exceeds the available fault current, with the 110.24 field marking present on service equipment.
Overcurrent devices, including the panelboards containing them, shall not be located in which space of a dwelling unit?
The former 42-circuit limit for lighting and appliance panelboards was: