Powell Electrical Systems, Inc.
Guide Specification
Low and Medium Voltage Metal-Enclosed Cable Bus
1.0
2.0
General
1.1
This specification describes the electrical and mechanical requirements for metal-enclosed, nonsegregated 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.
1.2
This 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.
Standards and Codes
2.1
3.0
4.0
The assemblies shall be constructed, wired, and tested in accordance with all applicable sections
of the latest listed standards and codes.
2.1.1
American National Standards Institute (ANSI IEEE-C37.23-1987)
2.1.2
National Electric Code (NEC) (NFPA No. 70)
2.1.3
National Electrical Manufacturers Association (NEMA)
2.1.4
IEEE-IPCEA Power Cable Ampacities
2.2
It 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.
2.3
Site Conditions
2.3.1
Ambient air temperature limits (-30°C To +40°C)
2.3.2
Altitude above sea level ______ feet.
2.3.3
Maximum wind velocity ______ miles per hour.
2.3.4
Ice load ______ pounds per square foot.
2.3.5
Snow load ______ pounds per square foot.
2.3.6
Seismic zone ______.
Basic Construction
3.1
The 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.
3.2
Outdoor installations shall be ventilated with louvered top and bottom covers.
3.3
Indoor installations shall be ventilated with louvered top and bottom covers.
Ratings (Current ratings based on 40°C ambient)
4.1
Maximum voltage ______ V/kV rms
4.2
Basic impulse insulation level ______ kV
4.3
Rated frequency withstand ______ kV (1 min. dry) 60Hz
4.4
Rated continuous current ______ Amperes
4.5
Momentary withstand current ______ kA Asymmetrical 167mS
4.6
Temperature rise of splice joints shall not exceed cable temperature, and in no case shall the splice
joint temperature rise exceed 50°C.
Publication No. 05184
06/2012 v0
©2012 Powell Industries, Inc. All rights reserved.
Page 1 of 4
Powell Electrical Systems, Inc.
Guide Specification
Low and Medium Voltage Metal-Enclosed Cable Bus
4.7
5.0
6.0
7.0
8.0
9.0
Enclosure total temperature limit 80°C.
Conductors
5.1
Phase 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.
5.2
Conductor supports must be provided to withstand short circuit currents and remain functional after
short circuit has been experienced.
Cable Terminations and Bus Joints
6.1
Contact 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.
6.2
Standard 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). Nonmagnetic hardware shall be supplied when specified.
6.3
All 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.
Grounding
7.1
The 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.
7.2
The housing ground continuity shall be maintained at the shipping splits, by using housing ground
splice plates.
Conductor Support Systems
8.1
The 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-tocenter spacing of 36 inches for horizontal bus, and 18 inches for vertical bus.
8.2
Insulating supports shall be fabricated from clear, non-toxic treated and painted hard maple or
molded glass reinforced polyester.
8.3
The support blocks shall be assembled with zinc dichromate treated steel hardware, to provide the
strength for the short circuit forces.
Enclosures
9.1
Enclosures 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.
9.2
The enclosure shall utilize aluminum side rails and top and bottom covers and have a non-painted
natural aluminum finish.
9.3
Enclosure shall be designed for a maximum temperature rise of 40°C when carrying rated current
in a 40°C ambient.
Publication No. 05184
06/2012 v0
©2012 Powell Industries, Inc. All rights reserved.
Page 2 of 4
Powell Electrical Systems, Inc.
Guide Specification
Low and Medium Voltage Metal-Enclosed Cable Bus
10.0
9.4
Removable 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.
9.5
Ventilated Indoor and Outdoor Construction
Top and bottom covers shall be ventilated.
9.5.2
Vent openings shall prohibit entrance of a 1/4" diameter rod.
9.5.3
Assembly hardware shall be stainless steel.
9.6
Enclosure joints shall provide adjustment to accommodate site variances and linear expansion of
up to 1/4 inch per splice.
9.7
Expansion Joints will be furnished for every straight run exceeding 80 feet, and at building
entrances when specified.
9.8
Enclosures are to be shipped in the longest practical lengths (up to 18 feet straight) to minimize
field assembly labor.
Wall or Floor Entrances
10.1
11.0
9.5.1
Duct 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.
Testing
11.1
Each 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.
11.2
Manufacturer may be requested to submit any ANSI-37.23-1987 design tests listed below.
11.2.1 Temperature Rise
11.2.2 Insulation Withstand
11.2.3 Impulse
11.2.4 Power Frequency Withstand
11.2.5 Momentary
11.2.6 Insulation Flame Retardance
11.3
12.0
13.0
In 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.
Drawing Requirements
12.1
Dimensioned drawings with plan and elevation views, and other views as necessary for clarity.
12.2
Cross-sectional drawings with views of cable interleaving, support block locations, and housing
arrangement.
12.3
Housing, seal assembly, and other assembly drawings.
12.4
Bus termination drawings showing details to connecting equipment (transformers, switchgear, etc.).
Installation and Operating Instructions
13.1
Installation and operating instructions shall cover all of the equipment furnished.
Publication No. 05184
06/2012 v0
©2012 Powell Industries, Inc. All rights reserved.
Page 3 of 4
Powell Electrical Systems, Inc.
Guide Specification
Low and Medium Voltage Metal-Enclosed Cable Bus
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: info@powellind.com
Website: powellind.com
Publication No. 05184
06/2012 v0
©2012 Powell Industries, Inc. All rights reserved.
Page 4 of 4