1.1. Bus The bus shall be 99 percent conductivity copper with tin- or silver-plated joints capable of carrying the rated continuous current without exceeding a temperature rise of 65 degrees Celsius, based on a 40 degrees Celsius ambient temperature. The copper bus shall be mounted and supported on porcelain insulators that shall withstand the forces due to momentary short circuit currents as listed per the City Engineer on specific projects. Each bus bar shall be epoxy insulated (fluidized bed epoxy) over its entire length except joint parts. Joints shall be insulated with removable boots (InsulBoot or approved equal) and jointed by double splice plates. They shall also be designed to withstand the vibration at the terminals as well as expansion and contraction of the busbars. The insulation shall be seamless to prevent infiltration of water and moisture. It shall also be flame-retardant to ensure safety in case of fire. A continuous ground conductor shall be provided in parallel with the primary conductors. The ground conductor may take the form of a separate bar, or the enclosure itself, if a continuous electrical path can be provided of the same momentary withstand current rating as the primary bus conductors. The ground conductor is preferably connected to the station ground at one point only, although more connection points are satisfactory if induced current loops have been avoided. The throat shall include flexible tin- or silver-plated copper braid connectors from the phase and neutral buses to the transformer secondary bushings and all connecting hardware necessary for the connection to the transformer bushings. Bus duct is used to connect new distribution transformer to existing metal clad switchgear. 1.2. Housing The materials for the bus duct enclosure shall be sheet metal suitably supported. All covers and panels shall not be less than MSG No.14 (nominal thickness of 1.9 mm or 0.0747 in). Panels or covers used to support devices shall be increased in thickness or otherwise strengthened, as necessary to support devices. The housing shall meet outdoor NEMA 3R requirements and painted to provide maximum protection against corrosion from water and other contaminants. All metal surfaces shall be protected from corrosion, the use of type 304 stainless steel or aluminum, constitute this protection without additional finishing. All hardware shall be stainless steel or aluminum, suitably protected to prevent corrosion. The enclosure shall have access covers with provided handles for installation and maintenance. The access covers shall be made with aluminum only. The access covers shall meet outdoor NEMA 3R requirements and painted to provide maximum protection against corrosion from water and other contaminants. All hardware of access covers shall be aluminum only, suitably protected to prevent corrosion. Flanges must be able to carry the structural load of the bus duct weight. The flanges shall be provided with gasket, nuts, bolts, spring washers, etc. The flange (which will be connected to the transformer side) shall be pre-drilled with holes in the factory. However, the flange (which will be connected to the switchgear side) shall not be predrilled with holes. 1.3. Finishes and color. All steel or aluminum surfaces to be painted shall receive a phosphatizing treatment or equivalent prior to application of paint. Painted internal surfaces shall be coated with at least one coat of corrosion-resisting paint. Painted external surfaces shall be coated with at least two coats of corrosion-resisting paint. The paint color shall be ANSI 70 Sky Gray.
