Powell Electrical Systems, Inc.
Guide Specification
Low and Medium Voltage Metal-Enclosed Cable Bus
1.0General
1.1This specification describes the electrical and mechanical requirements for metal-enclosed, non-segregated phase cable bus duct from 600V through 38kV applications. The cable bus system described is to be suitable for indoor or outdoor installations with nominal current ratings operating in ambient temperatures to 40°C.
1.2This specification covers only the general requirements of the cable bus duct assemblies. The specific requirements of each assembly (plan, arrangement, components, etc.) will be shown on drawings provided by the Purchaser. These drawings will form the basis for developing the drawings to manufacture and install.
2.0Standards and Codes
2.1The assemblies shall be constructed, wired, and tested in accordance with all applicable sections of the latest listed standards and codes.
2.1.1American National Standards Institute (ANSI IEEE-C37.23-1987)
2.1.2National Electric Code (NEC) (NFPA No. 70)
2.1.3National Electrical Manufacturers Association (NEMA)
2.1.4IEEE-IPCEA Power Cable Ampacities
2.2It shall be the manufacturer's responsibility to be knowledgeable of the requirements of the above Standards and Codes. Where standards or codes conflict, ANSI IEEE-C37.23-1987 shall be the governing document.
2.3Site Conditions
2.3.1Ambient air temperature limits (-30°C To +40°C)
2.3.2Altitude above sea level ______feet.
2.3.3Maximum wind velocity ______miles per hour.
2.3.4Ice load ______pounds per square foot.
2.3.5Snow load ______pounds per square foot.
2.3.6Seismic zone ______.
3.0Basic Construction
3.1The cable bus system shall be non-segregated phase type with adequate cable spacing as outlined in the latest edition of IEEE S-135/IPCEA P-46-426.
3.2Outdoor installations shall be ventilated with louvered top and bottom covers.
3.3Indoor installations shall be ventilated with louvered top and bottom covers.
4.0Ratings (Current ratings based on 40°C ambient)
4.1Maximum voltage ______V/kV rms
4.2Basic impulse insulation level ______kV
4.3Rated frequency withstand ______kV (1 min. dry) 60Hz
4.4Rated continuous current ______Amperes
4.5Momentary withstand current ______kA Asymmetrical 167mS
4.6Temperature rise of splice joints shall not exceed cable temperature, and in no case shall the splice joint temperature rise exceed 50°C.
4.7Enclosure total temperature limit 80°C.
5.0Conductors
5.1Phase conductors shall be flexible (Class B Stranded) copper or aluminum cables, insulated, shielded and jacketed in accordance with Purchaser's requirements, of sufficient cross-section to assure full current rating without exceeding a hot spot temperature rise of 50°C in an ambient air temperature of 40°C. Insulated cables are to be correctly interleaved, when practical, to assure balanced current between phase cables, and to give minimum cable temperature rise.
5.2Conductor supports must be provided to withstand short circuit currents and remain functional after short circuit has been experienced.
6.0Cable Terminations and Bus Joints
6.1Contact surfaces of cable terminals shall be adequately electrically plated. All bolted connections shall be capable of being properly tightened and locked in place, to provide and maintain full and uniform pressure under all operating conditions. Torque requirements in foot-pounds (ft.-lb.) shall be furnished by the manufacturer.
6.2Standard hardware shall be high strength plated steel; including bolts, nuts, flat washers, and (lock washers for copper connections), or (Belleville spring washers for aluminum connections). Non-magnetic hardware shall be supplied when specified.
6.3All transition parts for connections to other equipment terminals shall be provided by the bus manufacturer. The purchaser will provide the bus manufacturer with applicable coordination drawings to make the mating connections.
7.0Grounding
7.1The bus housing shall be designed to carry the system ground fault current without excessive temperature rise. When required a separate ground cable can be provided on the inside or outside of the bus enclosure. Separate ground bus may terminate to equipment, or to a ground pad for connection to the station ground.
7.2The housing ground continuity shall be maintained at the shipping splits, by using housing ground splice plates.
8.0Conductor Support Systems
8.1The individual cable bus conductors shall be supported to withstand the mechanical forces imposed by the momentary current rating specified. These supports shall have maximum center-to-center spacing of 36 inches for horizontal bus, and 18 inches for vertical bus.
8.2Insulating supports shall be fabricated from clear, non-toxic treated and painted hard maple or molded glass reinforced polyester.
8.3The support blocks shall be assembled with zinc dichromate treated steel hardware, to provide the strength for the short circuit forces.
9.0Enclosures
9.1Enclosures shall be constructed of aluminum to limit induced current losses and circulating currents. This results in a great reduction in the effects of hysteresis or magnetic heating.
9.2The enclosure shall utilize aluminum side rails and top and bottom covers and have a non-painted natural aluminum finish.
9.3Enclosure shall be designed for a maximum temperature rise of 40°C when carrying rated current in a 40°C ambient.
9.4Removable covers shall be provided throughout the bus duct run, both top and bottom, for ease in laying the cable and having access to bus joints and supports, without the need for disassembling the bus duct. Welded covers are unacceptable.
9.5Ventilated Indoor and Outdoor Construction
9.5.1Top and bottom covers shall be ventilated.
9.5.2Vent openings shall prohibit entrance of a 1/4" diameter rod.
9.5.3Assembly hardware shall be stainless steel.
9.6Enclosure joints shall provide adjustment to accommodate site variances and linear expansion of up to 1/4 inch per splice.
9.7Expansion Joints will be furnished for every straight run exceeding 80 feet, and at building entrances when specified.
9.8Enclosures are to be shipped in the longest practical lengths (up to 18 feet straight) to minimize field assembly labor.
10.0Wall or Floor Entrances
10.1Duct will include an internal vapor/fire barrier with one-half hour fire rating, at all wall, roof, and floor penetrations when required. Optional fire ratings up to 4 hours shall be supplied as required.
11.0Testing
11.1Each cable and its termination shall be given a high voltage DC hi-pot field acceptance test, at 75% of the factory voltage, following practices outlined by the cable manufacturer.
11.2Manufacturer may be requested to submit any ANSI-37.23-1987 design tests listed below.
11.2.1Temperature Rise
11.2.2Insulation Withstand
11.2.3Impulse
11.2.4Power Frequency Withstand
11.2.5Momentary
11.2.6Insulation Flame Retardance
11.3In lieu of actual testing, the manufacturer may submit design tests performed on similar ratings along with technical data to substantiate the adequacy of the equipment being furnished.
12.0Drawing Requirements
12.1Dimensioned drawings with plan and elevation views, and other views as necessary for clarity.
12.2Cross-sectional drawings with views of cable interleaving, support block locations, and housing arrangement.
12.3Housing, seal assembly, and other assembly drawings.
12.4Bus termination drawings showing details to connecting equipment (transformers, switchgear, etc.).
13.0Installation and Operating Instructions
13.1Installation and operating instructions shall cover all of the equipment furnished.
For assistance regarding these specifications or with support questions, please contact Powell directly:
Powell Electrical Systems, Inc.Delta/Unibus Division
515 Railroad Avenue
Northlake, IL 60164 / 708.409.1200
708.409.1211 fax
Email:
Website: powellind.com
Publication No. 0518406/2012 v0
©2012 Powell Industries, Inc. All rights reserved.
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