408.11 Special Services
(A) General. A special service switchboard or switchgear is defined as a switchboard or switchgear with a single disconnecting means having a frame rating in excess of 1200 amperes, or a sequence service switchboard where the sum of the frame sizes exceeds 1200 amperes. The following installation and construction shall apply to special service switchboards.
Informational Note: See 230.70 for permissible location(s) of the service disconnecting means.
(B) Drawing Submittal. The switchboard manufacturer who builds or assembles the special service equipment shall submit three sets of detailed drawings of the proposed equipment to the utility supply company. Upon acceptance, the utility shall retain one copy, stamp their acceptance and the available fault current, and forward them to the authority having jurisdiction.
The authority having jurisdiction shall review the drawings and notify the applicant of any changes, corrections, additions, or deletions required for approval. No switchboard shall be delivered or installed until the switchboard manufacturer has received approval from the authority having jurisdiction.
(C) Switchboard Rooms. The special service equipment shall be installed in a dedicated room of fire-resistant construction, accessible only to qualified persons. Where subject to possible flooding, such as below grade, sump pumps shall be provided and floor mounted switchboards shall be installed on a concrete pad a minimum of 102 mm (4 in.) above the nominal floor level.
Switchboard rooms containing equipment rated 3000 amperes or greater shall have two or more means of egress. Egress personnel doors shall be equipped with suitable listed hardware to provide egress from the room.
(D) Ability to Withstand Fault Current. Such special service equipment shall be so designed, constructed, and assembled that it is capable of withstanding and interrupting the available fault current without damage to itself or its related equipment.
(E) Identification. All service and feeder disconnecting means shall be prominently
identified by permanent means in accordance with 110.22.
(F) Barriers. All unprotected service bus shall be barriered or insulated to isolate the service busbars and terminals from the remainder of the switchboard. The exposed live or unprotected bus necessary to connect the line side of each switch shall be permitted to be un-isolated. The utility current transformers shall be in a barriered section conforming to the utility supply company requirements.
(G) Disconnecting Link. A disconnecting link shall be provided on the line side of the service switch or circuit breaker in the grounded conductor. Such link shall be located in the service switch or circuit breaker enclosure. In sequence switchboards, where each switch is permitted to have its own neutral disconnecting link, the location of the disconnecting link shall be provided on the switchboard cover.
(H) Bus Ampacity.
(1) Service entrance conductors and bus work on the line side of the service entrance switch(es) or circuit breaker(s) shall have an ampacity sufficient to carry the load supplied but shall not be less than 80% of the total rating of the service switch(es) or the frame size of the circuit breaker or breakers.
(2) When 100% rated switches or circuit breakers are used as the service disconnecting means, service entrance conductors and bus work shall have a rating of not less than 100% of the total rating of the service switch(es).
(3) Each switch or circuit breaker of the assembly shall be supplied by bus having an ampacity equal to the full rating of the switch or circuit breaker.
(I) Smallest Size Switch. Switches or circuit breakers need not be the same size; however, no switch or circuit breaker is permitted to be smaller than 400 amperes.
Exception No. 1: For a small emergency lighting load a switch sufficient in size for the load shall be permitted to be used. Such switch shall be mounted in the switchboard and shall be considered one of the six service disconnects.
Exception No. 2: On a sequence switchboard where the sum of the switches does not exceed 2400 amperes, 200 amperes shall be the minimum frame size.
(J) Maximum Electrical AC Service Size. The ampacity of any switchboard, switchgear or electrical ac service shall be limited to 4000 amperes. The maximum rating of any service disconnecting means shall be 3000 amperes. In a sequence service, which is a service with up to six disconnects, the sum of the disconnecting means shall not exceed 5000 amperes and no single disconnect shall exceed 3000 amperes. If the capacity requirements of an installation exceeds 4000 amperes, provisions for two or more electrical ac services shall be made.
(K) Complete Metal Enclosure. The switchboard or switchgear shall have a complete metal enclosure including bottom plates.
Exception: The bottom plates shall be permitted to be omitted when the switchboard is installed in a dedicated room of fire-resistant construction on a concrete pad where there is no opening between the walls of the switchboard and the pad. The conduit entries shall conform to 408.5 and shall be bonded as required by 250.94.
(L) Conduit Entries. All conduit entries to the ac service switchboard or switchgear shall have bonding bushings and their straps shall terminate on the bonding bus. Conduit entries to the switchboard or switchgear enclosure shall not be made within 10 in. of any live switchboard bus. Service entrance raceways shall enter the switchboard only in the service switch, cable transition, or current transformer sections. No other conductors shall pass through these sections. Feeder conduits and conductors shall terminate in the switchboard section from which they are supplied.
(M) Header Boxes. Header boxes shall contain not more than 30 conductors at any cross section and shall comply with 314.28(B). All header boxes shall be of the same construction as the switchboard.
(N) Bottom Boxes.
(1) Concrete gutters or trenches under switchboards or switchgear shall not be permitted.
(2) An under-switchboard or switchgear trench or gutter, in a dry location, lined with metal of the proper gauge to form an approved bottom box, and which is properly bonded to the switchboard or switchgear to form a complete enclosure shall be permitted. All conduit entries to this bottom box shall comply with (l) of this subsection.
Informational Note: A concrete slab in contact with the earth, or on the lowest level of a building is not a dry location.
(3) Where a bottom box is allowed in a wet location, the installation is subject to special review by the authority having jurisdiction. Complete drawings of the installation shall be submitted with the switchboard submittal, along with a request for special permission. A means to drain any accumulated moisture shall be provided.
(O) Maintenance. Required maintenance for special service equipment shall conform to 408.4.”
