rise on the buses, irrespective of the equipment
used. UL 845 allows 65 degrees temperature rise
only under certain conditions. In general this
means all buses must be plated and devices must be
UL labeled for the higher temperatures. If this is
not the case, the UL standard for temperature rise
is 50 degrees Celsius creating a conflict with NEMA.
The designer should be aware of this difference.
This specification references the UL standard and
bases the rise on the exceptions it permits.
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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] [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. The bus
ratings shall be based on a 65 degree Celsius maximum temperature rise in
accordance with UL 845 requirements. Bus shall have a short-circuit
current rating of not less than [42,000] [65,000] [100,000] RMS symmetrical
amperes. All bus work shall be supported on wet process porcelain
insulators, glass polyester, or suitable molded material.
2.6.2.1
Horizontal Bus
Each control center assembly shall be provided with a three-phase main
horizontal bus, with a continuous current rating not less than [600] [800]
[1,000] [1,200] amperes, located across the top of each vertical section.
The ends of horizontal buses shall be drilled for future extensions. [The
main horizontal bus shall be fully insulated.]
2.6.2.2
Vertical Bus
Each vertical section shall be provided with a three-phase vertical bus
with a continuous current rating of [300] [600] amperes connected to the
horizontal bus by brazing, welding, or bolting. Where the incoming feeder
breakers are located at the bottom of a control center, the vertical bus in
that section shall be rated the same as the main horizontal bus. Vertical
buses shall extend from the horizontal bus to the bottom of the lowest
available unit mounting space. The vertical bus shall be isolated from
wireways and equipment in compartments.
2.6.2.3
[Ground Bus
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NOTE: Delete this paragraph when not required.
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A copper [or aluminum] ground bus shall be provided full width at the
bottom of the motor control center line-up. 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.]
2.6.2.4
[Neutral Bus
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SECTION 16403A
Page 21
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