Panel boards
(i) General
All panelboards shall have a rating not less than the minimum feeder capacity required for the load calculated in accordance with [Article 220 NEC]. Panelboards shall be durably marked by the manufacturer with the voltage and the current rating and the number of phases for which they are designed and with the manufacturer's name or trademark in such a manner so as to be visible after installation, without disturbing the interior parts wiring.
(ii) Classification of Panelboards
Panelboards shall be classified for the purposes of this article as either lighting and appliance branch-circuit panelboards or power panelboards, based on their content. A lighting and appliance branch circuit is a branch circuit that has a connection to the neutral of the panelboard and that has overcurrent protection of 30 amperes or less in one or more conductors.
(A) Lighting and Appliance Branch-Circuit Panelboard A lighting and appliance branch-circuit panelboard is one having more than 10 percent of its overcurrent devices protecting lighting and appliance branch circuits.
(B) Power Panelboard A power panelboard is one having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch A power panelboard is a panelboard that has 10 percent or less of the installed overcurrent devices supplying lighting and appliance branch circuits. Any panelboard that is not classified as a lighting and appliance branch-circuit panelboard is a power panelboard. A typical power panelboard could be located near the service and be designed to supply facility feeder circuits. The feeders from a power panelboard supply other utilization equipment or other panelboards that supply either other branch circuits or other feeders.
(iii) Number of Overcurrent Devices on One Panelboard
Not more than 42 overcurrent devices (other than those provided for in the mains) of a lighting and appliance branch-circuit panelboard shall be installed in any one cabinet or cut-out box.
A lighting and appliance branch-circuit panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved.
For the purposes of [article 408 NEC], a 2-pole circuit breaker shall be considered two overcurrent devices; a 3-pole circuit breaker shall be considered three overcurrent devices.
(iv) Overcurrent Protection
(A) Lighting and Appliance Branch-Circuit Panelboard Individually Protected Each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard.
Exception No. 1: Individual protection for a lighting and appliance panelboard shall not be required if the panelboard feeder has overcurrent protection not greater than the rating of the panelboard.
A panelboard with main circuit breaker disconnect, suitable for use as service equipment.
An
arrangement of three individual lighting and appliance branch circuit
panelboards with main overcurrent protection remote from the
panelboards.
This shows the split-bus circuitry for a 200-ampere (left) and a 150-ampere (right) panelboard. The left panel has two 100-ampere main breakers installed as disconnecting means and 200-ampere main lugs. The right is a split-bus panel with 150-ampere main lugs and six main breaker disconnecting means. The 150-ampere panelboard is suitable for use as service equipment only if it is not a lighting and appliance panelboard or if it presently exists in an individual residential occupancy.
Circuitry for a 200-ampere (left) and a 150-ampere (right) split-bus panelboard.
(B) Power Panelboard Protection In addition to the requirements of 408.30, a power panelboard with supply conductors that include a neutral, and having more than 10 percent of its overcurrent devices protecting branch circuits rated 30 amperes or less, shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard
(C) Snap Switches Rated at 30 Amperes or Less Panelboards equipped with snap switches rated at 30 amperes or less shall have overcurrent protection of 200 amperes or less.
(D) Supplied Through a Transformer Where a panelboard is supplied through a transformer, the overcurrent protection required by (A), (B), and (C) shall be located on the secondary side of the transformer.
Exception: A panelboard supplied by the secondary side of a transformer shall be considered as protected by the overcurrent protection provided on the primary side of the transformer where that protection is in accordance with [240.21(C)(1) NEC].
(E) Delta Breakers A 3-phase disconnect or overcurrent device shall not be connected to the bus of any panelboard that has less than 3-phase buses. Delta breakers shall not be installed in panelboards.
(F) Back-Fed Devices Plug-in-type overcurrent protection devices or plug-in type main lug assemblies that are backfed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel.
(v)Enclosure
Panelboards shall be mounted in cabinets, cut-out boxes, or enclosures designed for the purpose and shall be dead-front.
Exception: Panelboards other than of the dead-front, externally operable type shall be permitted where accessible only to qualified persons.
(vi)Grounding of Panelboards
Panelboard cabinets and panelboard frames, if of metal, shall be in physical contact with each other and shall be grounded. Where the panelboard is used with non-metallic raceway or cable or where separate grounding conductors are provided, a terminal bar for the grounding conductors shall be secured inside the cabinet. The terminal bar shall be bonded to the cabinet and panelboard frame, if of metal; otherwise it shall be connected to the grounding conductor that is run with the conductors feeding the panelboard.
(vii)Switchboards in Damp or Wet Locations
Switchboards in damp or wet locations shall be installed as following:
Damp, Wet, or Hazardous (Classified) Locations:
Damp and Wet Locations In damp or wet locations, surface-type enclosures within the scope of this article shall be placed or equipped so as to prevent moisture or water from entering and accumulating within the cabinet or cut-out box, and shall be mounted so there is at least 6-mm ( 1/ 4-in.) airspace between the enclosure and the wall or other supporting surface. Enclosures installed in wet locations shall be weatherproof. For enclosures in wet locations, raceways or cables entering above the level of uninsulated live parts shall use fittings listed for wet locations.
Exception: Non-metallic enclosures shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.
The circuit breaker
(1) Miniature circuit breaker.
(2) Moulded case circuit breaker.
Standard ampere ratings for circuit breakers
-For miniature circuit breaker:
5, 10, 15, 20, 25, 32, 40, 50, 60, 63, 80.
-For moulded case circuit breaker:
100, 125, 160, 200, 250, 320, 400, 450, 630, 800, 1000, 1200, 1600, 2000, 3000, 4000, 5000, 6000.
The selection of circuit breaker is based on:
(1) Provide proper overload protection.
(2) Ensure a suitable voltage rating.
(3) Provide a sufficient interrupting current rating.
(4) Provide short circuit protection.
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