Each switchboard enclosure shall be NEMA type [2] [3R], built with selected
smooth sheet steel panels of not less than 1.9 mm No. 14 gage. Exposed
panels on the front and ends shall have bent angle or channel edges with
all corner seams welded and ground smooth. The front outside surfaces
shall not be drilled or welded for the purpose of attaching wires or
mounting devices if such holes or fastenings will be visible from the
front. The front panels shall be made in sections flanged on four sides
and attached to the framework by screws and arranged for ready removal for
inspection or maintenance. [Rear access to the bus and device connections
shall be provided.] Ventilating openings shall be provided as required and
shall preferably be of the grille type. All ventilating openings shall be
provided with corrosion-resistant insect-proof screens on the inside.
[Each switchboard shall be provided with a channel iron base at front,
rear, and sides, with exposed ends covered by welded steel plates. Grout
holes shall be provided. The switchboard sections shall be bolted to the
base.] [Switchboards shall be mounted as shown on the drawings and
mounting materials shall be furnished by the Contractor as indicated.] All
interior and exterior steel parts shall be treated to inhibit corrosion and
shall be painted as specified in paragraph PAINTING.
2.7.2
Bus
**************************************************************************
NOTE: When either copper or aluminum bus is allowed
the manufacturers will generally provide the less
expensive aluminum. Use ASTM 317 when aluminum bus
is permitted. Silver plating allows for a greater
temperature rise on the bus.
**************************************************************************
All buses shall be of copper [or aluminum] and [all bolted splices and
connections between buses and for extensions or taps for equipment] shall
be tin or silver-plated [throughout]. Copper [or aluminum] bars and shapes
for bus conductors shall conform to the applicable requirements of ASTM B
187/B 187M [, and ASTM B 317/B 317M]. All splices for field assembly shall
be bolted with at least two bolts and shall employ the use of "Belleville"
washers in the connection. Horizontal and vertical power buses have
minimum current ratings as shown on the drawings. The buses shall be
insulated for not less than 600 volts. Shop splices and tap connections
shall be brazed, pressure-welded or bolted. All splices for field assembly
shall be bolted. The buses shall be mounted on insulating supports of wet
process porcelain, glass polyester, or suitable molded material, and shall
be braced to withstand not less than [14,000] [22,000] [65,000] [_____]
symmetrical amperes ac.
2.7.3
[Grounding Bus
**************************************************************************
NOTE: Delete this paragraph when not required.
**************************************************************************
A copper [or aluminum] ground bus, rated not less than 300 amps, extending
the entire length of the assembled structure, shall be mounted near the
bottom of enclosure. A full clamp-type solderless copper or copper alloy
lug for No. 2/0 AWG stranded copper cable shall be provided at each end of
the bus for connection to the station grounding system.]
SECTION 16403A
Page 31
Previous Page
