Article 408: Switchboards and Panelboards

Article 408 Switchboards and Panelboards

I. General

Switchboards, panelboards, distribution boards, and battery-charging panels are covered.

Articles 240, 250, 314, 312, and 404 and applicable sections of other Code articles must be complied with.

They must be located to be free from damage and be secured. They must be arranged to avoid overheating due to induction. When used as service equipment, a grounding bar must be provided and it must be bonded to the case and frame. There is an exception for high-impedance grounded neutral system connections. Locations of terminals must be so as to avoid the necessity of reaching across ungrounded line bus. In a four-wire delta system the bar or conductor with the highest voltage to ground must be marked. Three-phase buses must have the phases A, B, C, front to back, left to right, or top to bottom when looking from the front. There is an exception for equipment in the same switchboard or panelboard as the meter. Refer to Section 373.6 for minimum wire bending space. Except for interconnections ands control wiring, only conductors intended for termination in a vertical section of a switchboard can be located there. There is an exception to this.

All circuits and modifications must be noted on a directory on the face or inside of the panelboard or on a switch on a switchboard. The circuits must be legibly identified in sufficient detail so that each circuit can be distinguished from another.

II. Switchboards

At least 900 mm (3 ft.) to a combustible ceiling. Around switchboard comply with 110.26.

Refer to Sections 250.17 through 250.178.

III. Panelboards

They must have current, voltage, phase, and manufacturer's trademark markings visible after installation. The rating may not be less than the feeder capacity. All circuits and modifications must be noted on a directory on the panelboard.

(A) Lighting and Appliance Branch-Circuit Panel-board. It falls into this category if 10% or more of the over-current devices protect lighting and appliance branch circuits which are circuits that are 30 amperes or less and have a neutral connection.

(B) Power Panelboard. It falls into this category if there are less than 10% of the overcurrent devices which protect lightning and appliance branch circuits.

Not more than 42 overcurrent devices can be installed in a lighting or appliance branch-circuit panelboard. This does not include mains. Each pole of a multipole circuit breaker is considered a single circuit.

(A) Individual overcurrent protection must be provided for a lighting and appliance branch-circuit panelboard of not more than two sets of circuit breakers or fuses. The overcurrent protection cannot exceed the ratings of the panelboard. This is not required if the feeder has overcurrent protection that does not exceed the rating of the panelboard. If an existing panelboard is used as service equipment in a single-residence occupancy, the individual protection is not required.

(B) A power panelboard with a supply neutral and more than 10% of the overcurrent devices protecting branch circuits 30 amperes or less must have supply side protection not greater than the rating of the panelboard.

(C) Overcurrent protection not greater than 200 A is required for a panelboard that has snap switches rated 30 A or less.

(D) For panelboards that are supplied through a transformer, the overcurrent protection required must be on the secondary of the transformer. There is an exception.

(E) A panelboard with less than three-phase buses cannot use a three-phase overcurrent device or disconnect. Delta breakers cannot be installed in panelboards.

(F) An additional means of fastening that requires a release other than a pull to release the device must be used for backfeed plug-in devices (plug-in overcurrent or plug-in main lug assemblies).

Refer to Section 312.2(A).

Panelboards must be in some type of enclosure with a dead front. If only qualified persons have access to the panelboards, dead fronts are not required.

Fuses must be installed on the load side of switches. There is an exception for service equipment.

Metal cabinets and frames must be in contact with each other and grounded. A terminal bar for grounding conductors must be inside the cabinet when separate grounding conductors or nonmetallic raceway or cable is used. If the panelboard frame and cabinet are metal, the terminal bar is bonded to them. If nonmetallic, the terminal bar is connected to the grounding conductor from the feeder. The terminal bar used for the grounding conductors must be identified and located where the connection is made from the grounded conductor to a grounding electrode in accordance with Article 250. An isolated ground conductor can pass through the panelboard with connection to the ground bar in accordance with Section 250.146(D).

IV. Construction Specifications

Must be made of moisture-resistant noncombustible material for switchboards.

Must be rigidly mounted.

Instruments must be protected and the rating must not exceed 15 A.

They must be in accordance with Articles 240 and 380.

Top and bottom wire bending space must be in accordance with Table 312.6(B). Side bending space must be in accordance with Table 312.6(A). Refer to this article in the NEC® for exceptions.

Refer to Table 408.36.