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Medium-Voltage Metal-Enclosed Bus

Rev1
IssuedOct 17, 2026
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1 Scope

NOTE This standard governs metal-enclosed bus built to IEEE C37.23 as one assembly: the conductors and the insulators that hold them, the bolted joints between sections, the enclosure and its enclosure type, the fittings that turn, offset, extend, and pass the run through a wall or floor, the flanges and flexible connectors that land the run on the equipment at each end, the supports that carry it, and the field work that puts the run into service. (1.1)
NOTE Metal-enclosed bus is a factory assembly of rigid conductors, one per phase, held on insulators inside a grounded metal enclosure, shipped in sections that bolt together into a continuous run between two pieces of equipment. It carries the current a cable bundle would need many parallel sets to carry, with no field-made terminations and no exposed conductor, and it is the connection a transformer secondary of several thousand amperes, a generator, or a tie between two switchgear lineups is usually built with. (1.2)
NOTE Three constructions share IEEE C37.23 and this standard. Nonsegregated-phase bus holds all three phase conductors in one enclosure with no barriers between them, and is the usual product; segregated-phase bus holds all three in one enclosure with a grounded metal barrier between phases; isolated-phase bus holds each phase conductor in its own enclosure, and is admitted under this standard for generator connections in self-cooled construction only. (1.3)
NOTE IEEE C37.23 covers metal-enclosed bus in the 600 V class as well as above it, and the 600 V class nonsegregated-phase bus that connects low-voltage switchgear or a switchboard to a transformer secondary or to a generator is governed by this standard, because it is a different product from UL 857 busway with a different listing and dielectric basis. (1.4)
NOTE The run is one assembly. Its short-circuit withstand, its enclosure type, and its enclosure ground path are properties of the sections, the joints, and the fittings together, and a section of another make, a field-cut length, or a joint made with substitute hardware removes the run from the condition under which it was rated. (1.5)
NOTE The following are governed elsewhere and are outside this standard: (1.6)
  • busway rated 600 V and below listed to UL 857, including its plug-in construction, under BuswayBuswayResolves to the current adopted revision.sync/busway
  • the metal-clad switchgear, the metal-enclosed interrupter switchgear, the unit substation, the transformer, the generator, the paralleling switchgear, or the drive the run terminates at, and the flange, throat, or terminal enclosure that equipment furnishes under its own standard, under Medium Voltage SwitchgearMedium Voltage SwitchgearResolves to the current adopted revision.sync/medium-voltage-switchgear, Metal Enclosed Interrupter SwitchgearMetal-Enclosed Interrupter SwitchgearResolves to the current adopted revision.sync/metal-enclosed-interrupter-switchgear, Secondary Unit SubstationsSecondary Unit SubstationsResolves to the current adopted revision.sync/secondary-unit-substations, Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers, Low Voltage SwitchgearLow Voltage SwitchgearResolves to the current adopted revision.sync/low-voltage-switchgear, Low Voltage SwitchboardsLow Voltage SwitchboardsResolves to the current adopted revision.sync/low-voltage-switchboards, GeneratorsEngine GeneratorsResolves to the current adopted revision.sync/generators, Generator Paralleling SwitchgearGenerator Paralleling SwitchgearResolves to the current adopted revision.sync/generator-paralleling-switchgear, and Medium Voltage DrivesMedium-Voltage Variable Frequency DrivesResolves to the current adopted revision.sync/medium-voltage-drives
  • the shielded medium-voltage cable, its terminations, and its raceway where a cable connection is made instead of a bus connection, under Medium Voltage CablesMedium-Voltage CablesResolves to the current adopted revision.sync/medium-voltage-cables
  • the through-penetration firestop system installed around the run where it passes through a rated wall or floor, under FirestoppingFirestoppingResolves to the current adopted revision.sync/firestopping
  • the design of the seismic restraint of the supports, under Vibration Isolation And Seismic RestraintVibration Isolation and Seismic RestraintResolves to the current adopted revision.sync/vibration-isolation-and-seismic-restraint
  • the grounding electrode system and the bonding of a system rated 1000 V and below, under Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding
  • nameplate and label material, lettering, and attachment, under Equipment LabelingElectrical Equipment LabelingResolves to the current adopted revision.sync/equipment-labeling
  • the code basis, enclosure-type selection practice, and general electrical execution declared once for the project, under Common Work Results ElectricalCommon Work Results for ElectricalResolves to the current adopted revision.sync/common-work-results-electrical
  • the short-circuit, coordination, and arc-flash studies, under Short Circuit StudyShort-Circuit StudyResolves to the current adopted revision.sync/short-circuit-study, Protective Coordination StudyProtective Device Coordination StudyResolves to the current adopted revision.sync/protective-coordination-study, and Arc Flash StudyArc-Flash Hazard AnalysisResolves to the current adopted revision.sync/arc-flash-study
  • field acceptance testing method, instruments, acceptance criteria, and the compiled test report, under Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.sync/electrical-acceptance-testing
NOTE The substation ground grid and the grounding of systems over 1000 V, to which the enclosure of a medium-voltage run is bonded at each end, are not yet owned by a SynC standard; forced-cooled isolated-phase bus for large generating units is a different product with its own cooling plant and is not covered by any standard in this library. (1.7)
1.8 Metal-enclosed bus, its fittings, and its joint hardware shall comply with IEEE C37.23, and where a Nationally Recognized Testing Laboratory lists metal-enclosed bus of the voltage class furnished, the bus shall be listed and labeled.
1.9 The routing, the mounting elevation, and the fitting arrangement of each run shall be as indicated on the bus duct routing plans and elevations.
1.10 Where a value stated on the one-line diagram for a particular run differs from the datasheet selection under this standard, the one-line diagram shall govern for that run.

2 Referenced Standards

2.1 Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 Where the contract documents, the Authority Having Jurisdiction, or two referenced standards impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
Standard Title
IEEE C37.23 Standard for Metal-Enclosed Bus
IEEE C37.100 Standard Definitions for Power Switchgear
IEEE C37.20.1 Standard for Metal-Enclosed Low-Voltage AC Power Circuit-Breaker Switchgear
IEEE C37.20.2 Standard for Metal-Clad Switchgear
IEEE C37.20.3 Standard for Metal-Enclosed Interrupter Switchgear
IEEE C37.121 Guide for Switchgear - Unit Substation - Requirements
IEEE C57.12.00 General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers
NEMA 250 Enclosures for Electrical Equipment (1000 Volts Maximum)
NFPA 70 National Electrical Code (Articles 110, 250, 300, and 368 Part IV)
NFPA 70E Standard for Electrical Safety in the Workplace
ANSI/NETA ATS Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems (Section 7.4)
ASTM B187 Copper, Bus Bar, Rod, and Shapes and General Purpose Rod, Bar, and Shapes
ASTM B317 Aluminum-Alloy Extruded Bar, Rod, Tube, Pipe, Structural Profiles, and Profiles for Electrical Purposes (Bus Conductor)
ASTM B209 Aluminum and Aluminum-Alloy Sheet and Plate
ASTM A1008 Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy
ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Chapter 13)
UL 857 Busways

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for review before any bus is released for manufacture:
  • shop drawings for each run giving the routing in plan and elevation, every section and fitting by designation and length, the joint locations, the support locations and type, the expansion provision locations, the wall and floor penetration locations, and the flange or terminal enclosure at each end
  • product data giving the bus type, the voltage class and insulation level, the continuous current rating and the temperature-rise basis it is established on, the short-time and momentary withstand current ratings, the conductor material, plating, and insulation, the insulator material, the enclosure material, ventilation, and enclosure type, and the enclosure ground path
  • the dimensions and weight of every section and fitting, and the weight per foot of the run for the structural engineer's review of the supports
  • the flange drilling, the conductor stab arrangement, and the phase sequence at every termination, coordinated with the manufacturer of the equipment at that end
  • the design test reports on which the insulation level, the continuous current rating, and the withstand ratings of the bus series rest
  • the seismic restraint arrangement of the supports, where the datasheet requires restraint
  • the manufacturer's installation instructions, including the joint torque values, the hardware schedule, and the support spacing for each orientation
Action Submittalscheckbox
☑ Shop drawings
☑ Product data with ratings and construction
☑ Dimensions and weights
☑ Termination flange drilling, stab arrangement, and phase sequence
☑ Design test reports
☐ Seismic restraint arrangement
☑ Installation instructions with torque values and support spacing
3.1.2 The Contractor shall field-measure the route of each run, including the as-set position of the equipment at each end where that equipment is already in place, and shall confirm the section and fitting schedule against the measured dimensions before the shop drawings are submitted.
NOTE Metal-enclosed bus is built to length at the factory and a run is ordered as a schedule of sections and fittings, so a dimension taken from the drawings rather than from the building and the equipment produces a run that does not close, and the correction is a special section on the manufacturer's lead time; this is why the field measurement precedes the submittal rather than the delivery. (3.1.3)
3.1.4 A run shall not be released for manufacture until the action submittals covering it have been reviewed and returned.

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following with or before the action submittals:
  • the manufacturer's qualification statement required under Quality Assurance
  • the qualifications of the firm and the technicians who will perform field acceptance testing
  • the manufacturer's published correction factors applied for ambient temperature and altitude, where either departs from the usual service conditions of IEEE C37.23
  • the manufacturer's published maximum straight run length between expansion provisions for the conductor material furnished
  • the manufacturer's statement of the enclosure ground path and the enclosure continuity provided at every joint
Informational Submittalscheckbox
☑ Manufacturer's qualification statement
☑ Field testing firm and technician qualifications
☐ Ambient and altitude correction factors
☑ Maximum run length between expansion provisions
☑ Enclosure ground path statement

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following before any run is accepted:
  • record drawings reflecting the as-installed routing, every joint, support, expansion provision, and penetration location
  • the certified factory production test report for the sections and fittings furnished
  • the field acceptance test report for each run, giving every measured value, the acceptance criterion applied, and the tester's determination
  • the joint torque record giving the value applied at every joint and every termination, by location
  • operation and maintenance data covering the bus series, the joint inspection interval, the insulator cleaning procedure, the space heater and breather maintenance on an outdoor run, and the procedure for adding a section to the run
  • the warranty certificate identifying each run by designation and the warranty commencement date
  • a signed receipt from the Owner for the spare parts delivered
Closeout Submittalscheckbox
☑ Record drawings
☑ Certified factory production test report
☑ Field acceptance test reports
☑ Joint torque record
☑ Operation and maintenance data
☑ Warranty certificate
☑ Spare parts receipt

4 Quality Assurance

4.1 Manufacturer Qualifications

4.1.1 The bus shall be produced by a manufacturer that has built metal-enclosed bus to IEEE C37.23 of the type and voltage class furnished for not less than the period indicated in the datasheet.
Manufacturer Experiencerange
years
351020
Default: Not less than 5 years
4.1.2 The manufacturer shall state in the qualification statement the period, measured from the date of manufacture, for which sections, fittings, joint hardware, and insulators compatible with the bus series furnished will remain available.
NOTE A bus series is extended with sections that mate with its own joint and its own enclosure profile, and no other maker's product mates with either, so the Owner who relocates a piece of equipment or adds a section ten years on is buying from the original manufacturer or replacing the run; the availability period is what makes that purchase possible. (4.1.3)

4.2 Source Limitations

4.2.1 The sections, the fittings, the joint hardware, the support brackets, the expansion provisions, the penetration fittings, and the termination flanges and flexible connectors of a run shall be furnished by the bus manufacturer as one product series.
4.2.2 Every run on the project shall be of one manufacturer's bus series, so that the spare joint hardware and the insulators interchange across runs.
4.2.3 No section or fitting shall be field-fabricated, field-cut, or field-drilled, and no joint shall be made with hardware other than the hardware furnished for the joint.

4.3 Field Testing Firm

4.3.1 Field acceptance testing shall be performed by the firm indicated in the datasheet.
Field Acceptance Testing Firmradio
○ Independent testing firm accredited to ANSI/NETA ATS
○ Manufacturer's field service organization
○ Installing contractor's own technicians
4.3.2 The technicians who perform field acceptance testing shall hold a current certification for medium-voltage equipment testing from NETA or from the bus manufacturer, and shall have tested metal-enclosed bus of the voltage class furnished.
NOTE An independent firm has no stake in whether the run passes and reports against a published acceptance standard; the manufacturer's organization knows the joint, the insulator, and the flexible connector best and is already on site where start-up services are furnished at the equipment the bus connects; the installing contractor's own technicians cost least and are available on the installer's schedule. Which of these the Owner wants depends on how the results will be used and on whether a report from the party who built or installed the run would satisfy the Owner's insurer and the Authority Having Jurisdiction, and an overpotential test at medium voltage calls for a test set and a competence the independent firm and the manufacturer's organization bring as a matter of course. (4.3.3)

5 Environmental and Service Conditions

5.1 Ambient Temperature

5.1.1 The bus shall carry its continuous current rating at the design ambient temperature of every space it passes through.
5.1.2 The design ambient temperature for an indoor run shall be as indicated in the datasheet.
Indoor Design Ambient Temperaturerange
°C
2530405055
Default: Not less than 40 °C
NOTE IEEE C37.23 establishes the continuous current rating at a 40 °C ambient, so a 40 °C design ambient is the condition at which the nameplate rating applies without correction; a higher value covers an electrical room whose ventilation cannot hold that ambient with the transformer at design load, or a turbine hall or a process area that runs hotter, at the cost of a larger bus for the same load. (5.1.3)
5.1.4 A run installed outdoors, or in a space that follows the outdoor temperature, shall be rated for Site Ambient Temperature MaximumSite Ambient Temperature MaximumParameterEach project supplies its own value.site-ambient-temperature-maximum where that temperature exceeds 40 °C, and the manufacturer shall state the correction applied in the informational submittals.
5.1.5 Where a run passes through a space whose ambient exceeds the design ambient, the correction for that space shall apply to the whole run, because the current the run carries is the same at every point along it.

5.2 Altitude

5.2.1 The bus shall be corrected for AltitudeAltitudeParameterEach project supplies its own value.altitude in accordance with the altitude correction factors of IEEE C37.23, for both dielectric strength and continuous current, where the altitude exceeds the 1000 m usual service condition of that standard.
NOTE Air thins with altitude, which reduces the dielectric strength of the air clearances between the conductors and the enclosure and the convective cooling that sets the continuous current rating, so a run rated at sea level carries less insulation margin and less current at elevation than its nameplate states, and the insulation level is the rating that gives way first. (5.2.2)
5.2.3 Ambient temperature correction and altitude correction shall be applied cumulatively where both conditions apply.

5.3 Seismic Restraint

5.3.1 The seismic restraint required for the supports of each run shall be as indicated in the datasheet.
Seismic Restraint Requirementselect
Not required
Restraint of the supports per ASCE 7 Chapter 13
Derived — Seismic Design CategorySeismic Design CategoryParameterEach project supplies its own value.seismic-design-category and the component importance factor assigned to the bus under ASCE 7 Chapter 13 (by default)
NOTE Whether the run must be restrained follows from the seismic design category and from the importance factor the code assigns to the equipment it connects, so the field carries the consequence of those inputs rather than a preference; a run that connects the generator a Risk Category IV facility depends on carries the higher importance factor and is restrained in a category where an ordinary run is not. (5.3.2)
5.3.3 Where seismic restraint is required, it shall be designed and installed in accordance with the seismic provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code, ASCE 7 Chapter 13, and Vibration Isolation And Seismic RestraintVibration Isolation and Seismic RestraintResolves to the current adopted revision.sync/vibration-isolation-and-seismic-restraint, and the restraint shall attach to the support or the enclosure only at the points the bus manufacturer designates for it.
5.3.4 Where seismic restraint is required, the restraint shall not prevent the thermal movement the expansion provisions are furnished to absorb, and a restrained run shall be braced on one side only of each expansion provision.
5.3.5 Where seismic restraint is required, the restraint shall not transmit the seismic load of the run into the equipment at either end, and the flexible connector at each termination shall be sized for the relative displacement the restraint design assigns between the run and the equipment.

6 Bus Type and Ratings

6.1 Bus Type

6.1.1 The bus type of each run shall be as indicated in the datasheet.
Bus Typeselect
Nonsegregated-phase bus
Segregated-phase bus
Isolated-phase bus
NOTE Nonsegregated-phase bus holds the three conductors in one enclosure a few inches apart, which gives the smallest cross-section and the lowest cost per foot, and is the construction a transformer-to-switchgear connection, a switchgear tie, and a 600 V class connection are built with on nearly every project; its one enclosure means a phase-to-ground fault at one conductor can involve the others. Segregated-phase bus adds a grounded barrier between phases in the same enclosure, which confines a fault to one phase for the time the protection takes to clear it and is chosen where a phase-to-phase fault at the bus would be intolerable, at a cost in width and in the barrier at every joint. Isolated-phase bus gives each conductor its own enclosure, spaced apart, so that a phase-to-phase fault at the bus cannot occur and the magnetic forces of a through-fault act on the enclosures rather than on the conductors, and it is the construction a generator of several thousand amperes is connected with. The type is a judgment on fault consequence and on current against cost, and no one type is the norm across the projects this standard serves, so the field asserts no default. (6.1.2)
6.1.3 Where isolated-phase bus is selected, the run shall comply with the Isolated-Phase Bus article in addition to the articles that apply to every type.
6.1.4 Where a run changes type along its length, the change shall be made at a transition fitting of the same series, and the location of the change shall be as indicated on the bus duct routing plans and elevations.

6.2 Voltage Class and Insulation Level

6.2.1 The voltage class of each run shall be as indicated in the datasheet.
Voltage Classselect
600 V class
5 kV class
8.25 kV class
15 kV class
27 kV class
38 kV class
Per drawings — the one-line diagram (deferred by default)
NOTE The voltage class is the rated maximum voltage of IEEE C37.23 that the system voltage on the one-line diagram falls within, and it fixes the clearances, the insulators, and the insulation level the run is built to; the 600 V class serves a 480 V or 600 V switchgear connection, the 5 kV class a 2.4 kV or 4.16 kV system, the 8.25 kV class a 6.9 kV system, the 15 kV class a 12.47 kV or 13.8 kV system, and the 27 kV and 38 kV classes the 24.9 kV and 34.5 kV systems a site takes service at. A run is ordered to the class of the system it serves, and a run built to a higher class than the system costs more clearance and more enclosure without changing the system. (6.2.2)
6.2.3 The rated maximum voltage of the bus shall equal or exceed the maximum operating voltage of the system it serves, and where the run is fed from a transformer secondary the Contractor shall confirm the class against the secondary voltage of the transformer before the run is released for manufacture.
6.2.4 The basic impulse insulation level of each run shall be as indicated in the datasheet.
Basic Impulse Insulation Levelselect
Not assigned, power-frequency withstand only (600 V class)
60 kV
75 kV
95 kV
125 kV
150 kV
Derived — the voltage class, per the rated insulation levels of IEEE C37.23, corrected for AltitudeAltitudeParameterEach project supplies its own value.altitude (by default)
NOTE IEEE C37.23 assigns each voltage class one rated insulation level, stated as a lightning impulse withstand and a one-minute power-frequency withstand, and assigns the 600 V class a power-frequency withstand only; the class selects the level, and the altitude correction factor of the same standard reduces the withstand the bus delivers at elevation, so a site above the usual service condition is served by a bus of the next class or by a derated acceptance of the standard level, as the manufacturer's correction states. (6.2.5)
6.2.6 The insulation level of the run shall be not less than the insulation level of the switchgear, transformer, or generator terminal it connects to, so that a surge entering the run is withstood by the run before it reaches the equipment.

6.3 Continuous Current Rating

6.3.1 The continuous current rating of each run shall be as indicated in the datasheet.
Continuous Current Ratingrange
A
600120016002000250030003500400050006000700080001000012000150002000025000300004000050000
Per drawings — the one-line diagram (deferred by default)
NOTE The rating of a run is fixed by the full-load current of the transformer, the generator, or the switchgear main it connects, including any forced-cooled stage of the transformer the project intends to use, and it is stated on the one-line diagram with that equipment; a run cannot be uprated after manufacture without replacing every section that carries the current, which is why the rating is chosen against the ultimate rating of the equipment rather than its first-day load. The ratings above 6000 A are the territory of isolated-phase bus. (6.3.2)
6.3.3 The continuous current rating shall be established at the temperature-rise limits IEEE C37.23 assigns to the plating of the connections and to the enclosure surfaces, over a 40 °C ambient, and the manufacturer shall state the rise basis in the product data.
NOTE IEEE C37.23 holds a silver- or tin-plated connection to a 65 °C rise over a 40 °C ambient and a bare connection to a 30 °C rise, and it holds the enclosure surface a person can touch to a lower rise still, so the plating at the joints and the enclosure cooling together set how much current a given conductor section carries; this is why every medium-voltage bus plates its joints and why a ventilated or an aluminum enclosure appears at the higher ratings. (6.3.4)
6.3.5 The bus shall carry its continuous current rating in every mounting orientation in which it is installed, or the manufacturer shall state the correction for each orientation in the informational submittals, and the rating after correction shall be not less than the rating the datasheet indicates.

6.4 Short-Circuit Withstand Ratings

6.4.1 The available fault current at each run shall be as indicated on the one-line diagram.
6.4.2 The short-time withstand current rating of each run, including every section, joint, fitting, and flexible connector in it, shall equal or exceed the available fault current at the run as established under Short Circuit StudyShort-Circuit StudyResolves to the current adopted revision.sync/short-circuit-study, for the duration IEEE C37.23 establishes the rating over, and shall be as indicated in the datasheet.
Short-Time Withstand Current Ratingrange
kA
10202531.540506380100120150200
Per drawings — the one-line diagram (deferred by default)
6.4.3 The momentary withstand current rating of the run shall be the peak current IEEE C37.23 assigns to the short-time withstand current rating, and the manufacturer shall state both ratings in the product data.
NOTE The short-time rating is the symmetrical current the conductors, the insulators, and the joints carried for the rated duration without damage in the design test, and the momentary rating is the peak of the first loop of that current, which is the force the insulators see; the two are fixed in a ratio by IEEE C37.23, so the project states the short-time rating and the momentary rating follows. The rating of a run is the lowest rating among its sections and fittings, so one fitting of a lower rating sets the rating of the whole run, and a generator connection is rated for the generator contribution and the system contribution together, which is the condition the study reports at that bus. (6.4.4)
6.4.5 Where the one-line diagram relies on a current-limiting device ahead of the run to reduce the fault current the bus sees, the reduced rating shall be applied only where the manufacturer has established the bus withstand for use with that device as a tested combination, and the combination shall be identified in the action submittals.

6.5 System Frequency

6.5.1 The system frequency shall be as indicated in the datasheet.
System Frequencyradio
● 60 Hz
○ 50 Hz
NOTE The momentary withstand peak factor and the enclosure losses both depend on the frequency, so a 50 Hz run is rated as a 50 Hz product rather than relabeled from a 60 Hz one. (6.5.2)

7 Conductors and Joints

7.1 Conductor Material

7.1.1 The conductor material shall be as indicated in the datasheet.
Conductor Materialradio
○ Copper
○ Aluminum
NOTE Copper carries more current per unit cross-section, which gives a smaller enclosure for the same rating, has the lower contact resistance at a bolted joint, and costs more; aluminum is lighter and less expensive for the same rating, which matters on a long outdoor run between a transformer and a building where the support load and the material cost scale with the length, and its joints depend on the plating and on the joint hardware to hold their resistance through thermal cycling. Copper is chosen where the room is tight, where the atmosphere attacks aluminum, or where the equipment at each end is copper and the Owner wants one metal throughout; aluminum is chosen where the run is long, the current is high, and the weight carried by the structure matters, and it is the conductor nearly every isolated-phase bus is built with. Neither is distinctly the norm across projects, so the field asserts no default. (7.1.2)
7.1.3 Where copper is selected, the conductors shall be copper bus bar or tube conforming to ASTM B187 with a conductivity of not less than 98% IACS.
7.1.4 Where aluminum is selected, the conductors shall be an aluminum alloy bus conductor conforming to ASTM B317 with a conductivity of not less than 55% IACS.
7.1.5 Where aluminum is selected, every joint between an aluminum conductor and a copper terminal, stab, or flexible connector at the equipment shall be made through a plated contact surface suitable for the combination, with hardware and washers the manufacturer designates for a bimetallic joint.

7.2 Joint Plating

7.2.1 The plating of the conductors at every joint and termination shall be as indicated in the datasheet.
Joint Platingradio
○ Silver-plated
○ Tin-plated
Manufacturer's standard (by default)
7.2.2 The manufacturer shall state the joint plating in the product data.
NOTE Silver plating has the lower contact resistance in a clean atmosphere and is the plating IEEE C37.23 names for the full connection temperature rise, and it is what most medium-voltage bus is built with as standard; tin plating resists the sulfur compounds that blacken silver and raise its contact resistance, and holds its resistance where the atmosphere carries hydrogen sulfide, as in a wastewater facility or near a digester. Each bus series is built with one plating as its standard, and that standard serves every ordinary installation, which is why the field starts in the manufacturer's standard state and is changed where the atmosphere calls for it. (7.2.3)
7.2.4 Plating shall be continuous over every joint contact surface and every termination contact surface, and a bare contact surface shall not be furnished at any joint that carries the continuous current rating.

7.3 Conductor Insulation

7.3.1 The conductor insulation shall be as indicated in the datasheet.
Conductor Insulationradio
○ Insulated conductors
○ Bare conductors on insulators
NOTE An insulated conductor carries a bonded insulation over its full length, which lets the conductors sit closer together for the same voltage class, holds a phase-to-ground fault off the conductor surface while the protection clears it, and keeps a dropped tool or a settled film of dust from bridging a clearance; it costs the insulation and it makes the joints a point where the insulation is removed and restored with a boot or a tape system. A bare conductor on insulators depends on air clearance alone, is the construction of a ventilated enclosure and of isolated-phase bus, and is inspected and cleaned by eye, and it is what a 600 V class run and a high-current generator run are usually built with. Which a project wants depends on the voltage class, on the atmosphere, and on the enclosure selected, and neither is distinctly the norm across the whole range this standard covers, so the field asserts no default. (7.3.2)
7.3.3 Where insulated conductors are selected, the insulation shall be a fluidized-bed epoxy coating or an equivalent bonded insulation rated for the voltage class and for the maximum conductor temperature at rated current, applied over the full length of every conductor and over every fitting conductor, and every joint shall be insulated after it is made up with a boot or a tape system the manufacturer furnishes for the joint, rated for the same voltage class.
7.3.4 Where bare conductors are selected, the clearance from each conductor to the enclosure and between conductors shall be not less than the clearance IEEE C37.23 requires for the insulation level, measured with the conductor at the deflection the momentary withstand current produces.

7.4 Support Insulators

7.4.1 The conductors shall be supported on insulators of porcelain, glass-reinforced polyester, or cycloaliphatic epoxy, rated for the insulation level of the run, track-resistant and non-hygroscopic, and spaced so that the conductors withstand the momentary withstand current without permanent deformation and without contact between phases or with the enclosure.
7.4.2 Each insulator shall be attached to the enclosure and to the conductor so that the conductor is free to move along its length with temperature at every insulator except the anchor points the manufacturer designates, and the insulator shall not carry the thermal load of the conductor.
7.4.3 An insulator that is cracked, chipped, or contaminated shall be replaced before the run is energized, and no insulator shall be repaired in the field.

7.5 Bolted Joints

7.5.1 Each joint between two sections or fittings shall be a bolted joint furnished by the manufacturer, shall carry the continuous current rating and the short-time withstand rating of the run, and shall be made with the bolts, nuts, and conical spring washers furnished for it.
7.5.2 Joint hardware shall be plated steel or silicon bronze as the manufacturer designates for the conductor material and plating, and a joint between an aluminum conductor and any other metal shall be made with the hardware and the contact treatment the manufacturer designates for the bimetallic joint.
7.5.3 Each joint shall be accessible after installation through a removable enclosure cover for torque verification, for insulation of the joint where the conductors are insulated, and for infrared inspection under load, and no joint shall be located within a wall, a floor, or a penetration fitting.
7.5.4 Each joint cover shall maintain the enclosure type of the run and shall be removable without disturbing the adjacent sections, so that a section or a fitting can be removed and replaced in a completed run.

8 Enclosure

8.1 Enclosure Material

8.1.1 The enclosure material shall be as indicated in the datasheet.
Enclosure Materialradio
○ Aluminum
○ Steel
NOTE An aluminum enclosure is non-magnetic, so the alternating field of the conductors induces no hysteresis loss in it and the eddy loss it does carry is small, which keeps the enclosure cool at high current and is why aluminum is the norm where the continuous current is high, roughly from 3000 A upward, and on every isolated-phase run; it weighs less per foot, which lowers the support load on a long run, and it corrodes less in a damp atmosphere. A steel enclosure is stiffer across a long support span, resists impact where the run is reached by a lift truck or a falling object, and costs less at the lower ratings, where the enclosure loss is small enough not to matter, and it is what many 600 V class and low-current medium-voltage runs are built with. Each is the norm in its own part of the current range and neither is distinctly the norm across the whole range, so the field asserts no default. (8.1.2)
8.1.3 An aluminum enclosure shall be an aluminum alloy sheet or extrusion conforming to ASTM B209 or ASTM B317, and a steel enclosure shall be a cold-rolled carbon steel sheet conforming to ASTM A1008, galvanized or finished so that no bare steel is exposed inside or outside the enclosure.
8.1.4 The enclosure shall be of a thickness and a section that spans the manufacturer's maximum support spacing in every orientation shown on the shop drawings without a deflection that bears on a joint or an insulator, and the manufacturer shall state the spacing for each orientation in the installation instructions.

8.2 Enclosure Ventilation

8.2.1 The enclosure ventilation shall be as indicated in the datasheet.
Enclosure Ventilationradio
● Non-ventilated
○ Ventilated
NOTE A non-ventilated enclosure is sealed against the air around it, keeps dust, moisture, and vermin off the conductors and the insulators, is the only construction an outdoor run or a run through a floor is built with, and is what nearly every medium-voltage run is built with, which is why it is the default; a ventilated enclosure carries screened louvers that pass convective air over the conductors, which raises the current a given conductor section carries and is chosen for an indoor high-current run in a clean room, at the cost of admitting whatever the room air carries. (8.2.2)
8.2.3 A run installed outdoors, through a floor, in a space used for environmental air, or in a damp or wet location shall be of non-ventilated construction, whatever the datasheet selects.
8.2.4 Where a ventilated enclosure is furnished, the openings shall be screened and arranged so that no part of a conductor or an insulator is reached by a rod of the diameter IEEE C37.23 and NFPA 70 368.240 specify, and the openings shall be placed so that the air entering them is not drawn from a space that carries conductive dust or corrosive vapor.

8.3 Enclosure Type

8.3.1 The enclosure type shall be as indicated in the datasheet.
Enclosure Typeradio
○ Indoor, Type 1
○ Outdoor, Type 3R
NOTE A transformer-to-switchgear run crosses from a transformer in a yard to switchgear in a building on as many projects as it runs down an electrical room, and a generator run crosses from an outdoor enclosure or a generator building as often as it stays indoors, so neither type is distinctly the norm and the field asserts no default; the outdoor type carries the gasketing, the drains, the sloped covers, and the outdoor provisions of the Outdoor Provisions article, and costs more per foot for them. (8.3.2)
8.3.3 The enclosure type shall be designated in accordance with NEMA 250 for the 600 V class and in accordance with IEEE C37.23 for the indoor or outdoor construction above it, and the type shall be marked on the enclosure.
8.3.4 A run installed outdoors, in a wet location, or where it is exposed to rain or to water from washing shall be of the outdoor construction, whatever the datasheet selects.
8.3.5 Where a run passes from indoors to outdoors, the transition shall be made with a wall flange and a weather seal the manufacturer furnishes for the bus series, the outdoor portion shall be of the outdoor construction up to and through the wall, and the run shall be arranged so that water entering at the transition drains outdoors and does not reach an indoor joint.
8.3.6 A run installed where the atmosphere carries salt, chemical vapor, or another corrosive agent, including a coastal site exposure, a wastewater facility, or a chemical process area, shall have an enclosure, hardware, and insulators the manufacturer states in writing are suitable for that atmosphere.

8.4 Outdoor Provisions

8.4.1 Requirements in this article apply where the outdoor construction is selected in the datasheet or required by the Enclosure Type article.
8.4.2 An outdoor run shall be furnished with the provisions indicated in the datasheet.
Outdoor Provisionscheckbox
☑ Thermostatically controlled space heaters
☑ Drain openings at every low point
☑ Filtered breathers
8.4.3 Where space heaters are furnished, they shall be sized to hold the interior of the enclosure above the dew point at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum, shall be controlled by a thermostat or a humidistat, shall be fed from a source the one-line diagram designates, and shall be located so that no heater is within the clearance of a conductor or bears on an insulator.
8.4.4 Where drain openings are furnished, they shall be screened, shall be located at every low point of the outdoor portion of the run and at each side of every wall penetration, and shall be arranged as NFPA 70 368.239 requires so that condensation drains without pooling on an insulator or a joint.
8.4.5 Where filtered breathers are furnished, they shall be located at the high points of the outdoor portion of the run and shall carry a replaceable filter element.
NOTE An outdoor enclosure breathes as it heats and cools through the day, drawing in moist air that condenses on the cold conductors at night; the heaters hold the interior above the dew point, the drains carry out what condenses anyway, and the breathers let the enclosure breathe through a filter rather than through a gasket, and a run furnished with only one of the three fails its insulation resistance test the first wet season. (8.4.6)
8.4.7 Outdoor enclosure covers shall be sloped or crowned to shed water, every seam and cover shall be gasketed, and every bolt that passes through the enclosure wall shall be sealed.

8.5 Enclosure Finish

8.5.1 The finish of the enclosure shall be as indicated in the datasheet.
Enclosure Finishselect
ANSI 61 light gray paint
ANSI 49 medium gray paint
Unpainted aluminum
Custom color matched to a sample furnished by the Owner
Manufacturer's standard (by default)
8.5.2 The manufacturer shall state the enclosure finish in the product data.
NOTE ANSI 61 is the gray the switchgear and the transformer on a project most often match; an unpainted aluminum enclosure is what some series ship as and serves a yard or a generator building nobody sees; a custom color is chosen where the run is exposed in a finished space or where the Owner color-codes the system it serves. (8.5.3)
8.5.4 A painted enclosure shall carry a baked powder coat or enamel finish over a pretreatment, and a painted outdoor enclosure shall carry a finish the manufacturer has qualified for outdoor exposure under IEEE C37.23.

8.6 Enclosure Grounding Continuity

8.6.1 The enclosure shall be electrically continuous over the full length of the run, including every joint, fitting, cover, expansion provision, and penetration fitting, and the manufacturer shall state in the informational submittals the enclosure ground path and the means by which continuity is provided at every joint.
8.6.2 Where the enclosure sections are joined through a painted or gasketed joint, the continuity shall be provided by a bonding jumper or a bonding strap at the joint, sized for the short-time withstand current of the run, and not by the bolts alone.
8.6.3 The enclosure shall be bonded to the ground bus of the switchgear at one end and to the ground bus, the tank ground pad, or the frame ground of the equipment at the other end, with a conductor sized for the ground-fault current the run can carry, as NFPA 70 368.238 requires.
8.6.4 Where the run is in the 600 V class, the bonding of the enclosure and the sizing of the bonding conductors shall comply with Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding.
NOTE A ground fault on a conductor returns through the enclosure to the source, and a joint whose only bond is a set of bolts through paint carries that current through the threads until they arc; the bonding strap at every joint is what makes the enclosure a conductor rather than a set of boxes, and the bond at each end is what connects it to the ground system the protection trips on. (8.6.5)

9 Isolated-Phase Bus

9.1 Requirements in this article apply where isolated-phase bus is selected in the datasheet.
9.2 Each phase conductor shall be held in its own enclosure, and the three enclosures shall be spaced apart as the manufacturer's design for the momentary withstand current requires.
9.3 The enclosures shall be electrically continuous over the full length of the run and shall be bonded together at each end through short-circuit plates, so that the enclosure currents induced by the conductor currents circulate through the three enclosures and the plates as a closed loop.
NOTE The continuous enclosure with short-circuit plates at the ends carries, in each enclosure, a current nearly equal and opposite to its conductor current, which cancels the magnetic field outside the enclosures, removes the heating of nearby steel the field would otherwise cause, and reduces the forces on the conductors during a through-fault to a fraction of what an open enclosure would see; this is why the enclosure of an isolated-phase bus is a conductor in its own right, sized for current, and not a cover. (9.4)
9.5 The conductors and the enclosures shall be self-cooled, with the continuous current rating established by natural convection and radiation alone, and no forced-air or forced-liquid cooling shall be furnished under this standard.
9.6 Each enclosure shall be furnished with the bonding, the insulation from the supporting structure, and the connection to the short-circuit plates the manufacturer designates, so that enclosure current does not flow through the supports or the building steel.
9.7 Where the run connects to a generator, the manufacturer shall furnish the enclosure terminal arrangement at the generator terminals in coordination with the generator manufacturer, and the connection to each generator terminal shall be made with a flexible connector sized for the generator terminal displacement.
9.8 Where the run is tapped for a generator breaker, a surge protection cubicle, or an excitation transformer, each tap shall be a factory fitting of the same series, and its enclosure shall be bonded into the enclosure loop.

10 Fittings and Terminations

10.1 Elbows, Offsets, and Tees

10.1.1 Elbows, offsets, tees, and transitions shall be factory fittings of the same series, rating, enclosure type, and construction as the sections they join, and shall be furnished in the configuration shown on the reviewed shop drawings.
10.1.2 Where the routing requires a fitting of a non-standard angle or length, the fitting shall be made by the manufacturer, and the field shall not alter a fitting to suit the routing.

10.2 Expansion Provisions

10.2.1 An expansion provision of the same series and rating, consisting of a flexible conductor connection and an enclosure expansion joint, shall be furnished in every straight run whose length exceeds the manufacturer's published maximum run length between expansion provisions for the conductor material furnished, at intervals not exceeding that length.
10.2.2 An expansion provision shall be furnished where a run crosses a building expansion joint shown on the structural framing plans, located at the joint, and the supports on each side of the provision shall allow the movement the provision is furnished to absorb.
10.2.3 An expansion provision shall be furnished where a run passes between two separately founded structures, including between an outdoor transformer pad and a building, located at the point where the run leaves one foundation for the other.
NOTE The conductors grow with temperature at a rate the conductor material sets, and the enclosure, which runs cooler, grows less, so a long run with no provision to take up the difference carries the thermal stress into the joints, the insulators, and the equipment terminals, where it loosens the joint hardware over the seasons and works the terminal; an aluminum conductor grows about half again as much as a copper one over the same temperature change, which is why the maximum run length is published per conductor material. (10.2.4)

10.3 Wall and Floor Penetration Fittings

10.3.1 Where a run passes through a wall or a floor, the penetration shall be made with a wall or floor flange fitting of the same series, and the fitting shall be located so that no joint lies within the thickness of the wall or floor.
10.3.2 Where a run passes through a wall that separates an outdoor space from an indoor space, a vapor seal shall be furnished in the run at the wall, as NFPA 70 368.234 requires, so that the outdoor portion of the enclosure does not breathe into the indoor portion.
10.3.3 Where a run passes through a fire-resistance-rated wall or floor, the fitting shall be a fire-rated penetration fitting the manufacturer furnishes for the bus series, carrying an internal fire barrier rated for the hourly rating of the assembly penetrated, and the opening around the fitting shall be closed with a through-penetration firestop system listed for a bus duct penetrating item and installed under FirestoppingFirestoppingResolves to the current adopted revision.sync/firestopping, so that the rating of the assembly is restored as NFPA 70 300.21 and Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code require.
NOTE The penetration fitting carries the barrier inside the enclosure, between the conductors, which is the path a fire would otherwise follow along the run from one side of the wall to the other, and the firestop system closes the annular space around the enclosure, which is the path it would follow around the run; each covers the opening the other cannot, and the fitting is the bus manufacturer's and the firestop system the firestop installer's. (10.3.4)
10.3.5 Where the fire-rated penetration fitting is furnished with insulated conductors, the fire barrier shall be rated with the conductor insulation in place, and the manufacturer shall confirm in writing that the firestop materials in contact with the enclosure do not reduce the bus rating.

10.4 Termination at Switchgear

10.4.1 Where a run terminates at metal-clad switchgear, metal-enclosed interrupter switchgear, low-voltage switchgear, a switchboard, a unit substation section, or paralleling switchgear, the bus end shall be a termination flange furnished by the bus manufacturer, drilled to mate with the bus entry flange that equipment's manufacturer furnishes under the standard governing that equipment, and the bus manufacturer shall coordinate the flange drilling, the conductor stab arrangement, the phase sequence, and the ground connection with the equipment manufacturer before either is released for manufacture.
10.4.2 The connection between the bus conductors and the equipment bus shall be made with flexible connectors of laminated copper or aluminum, furnished by the bus manufacturer, rated for the continuous current and the short-time withstand current of the run, and sized for the thermal movement and the alignment tolerance between the run and the equipment.
NOTE The flange on the equipment side, the bus connection inside the equipment, and the barrier at the entry are furnished by the equipment manufacturer under that equipment's standard, and the bus side is furnished under this standard; the drilling and the stab arrangement are coordinated between the two manufacturers because a mismatch found at installation is corrected by a new termination flange on the bus manufacturer's lead time. (10.4.3)
10.4.4 Where the run is in the 600 V class and terminates at a switchboard or low-voltage switchgear, the termination shall carry a neutral connection where the system is four-wire, and the neutral conductor shall be insulated from the enclosure and bonded only at the point Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding designates.

10.5 Transformer Throat Connection

10.5.1 Where a run terminates at a transformer, the bus end shall be a termination flange furnished by the bus manufacturer, drilled to mate with the bus duct throat flange or the medium-voltage bus duct entry the transformer manufacturer furnishes under Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers or Secondary Unit SubstationsSecondary Unit SubstationsResolves to the current adopted revision.sync/secondary-unit-substations, and the bus manufacturer shall coordinate the flange, the terminal positions, and the phase sequence with the transformer manufacturer before either is released for manufacture.
NOTE The termination flange under this standard is the mate of the bus duct throat flange those standards offer, and the two are one connection: the transformer manufacturer furnishes the flange on the tank or enclosure and the air terminal chamber behind it, and the bus manufacturer furnishes the flange on the run and the flexible connectors to the transformer terminals. (10.5.2)
10.5.3 The connection between the bus conductors and the transformer terminals shall be made with flexible connectors that accommodate the differential movement, thermal expansion, and vibration between the transformer and the run without transmitting load to the transformer bushings or terminals, and the bus shall be supported at the termination independently of the transformer.
10.5.4 Where the transformer is liquid-immersed, the termination shall be made through an air-filled terminal chamber on the transformer, so that no liquid-filled compartment communicates with the bus enclosure, and where the transformer is dry-type the termination shall be barriered so that the transformer ventilation air does not pass through the bus enclosure.
NOTE A transformer hums and warms, and the run beside it does neither to the same degree; a rigid bus between them works the transformer terminal through every load cycle until a connection loosens or a bushing cracks, which is why the flexible connector carries the compliance and the terminal carries none of the load. (10.5.5)

10.6 Generator and Drive Terminal Connection

10.6.1 Where a run terminates at a generator, the bus end shall be a terminal enclosure or a termination flange furnished by the bus manufacturer, mated to the generator terminal box or terminal enclosure the generator manufacturer furnishes under GeneratorsEngine GeneratorsResolves to the current adopted revision.sync/generators, and the connection to each generator terminal shall be made with a flexible connector sized for the generator vibration and the terminal displacement the generator manufacturer states.
10.6.2 Where a run terminates at a medium-voltage drive, the bus end shall be a termination flange mated to the bus entry the drive manufacturer furnishes under Medium Voltage DrivesMedium-Voltage Variable Frequency DrivesResolves to the current adopted revision.sync/medium-voltage-drives, and the connection shall be made with flexible connectors as at switchgear.
10.6.3 Where a generator run carries neutral grounding equipment, a surge protection cubicle, or generator current transformers in the run, each shall be a factory fitting of the same series, and the equipment within it shall be furnished under the standard that governs the generator or the paralleling switchgear.

10.7 Supports and Hangers

10.7.1 Each run shall be supported by support brackets, hangers, or cradles furnished or designated by the bus manufacturer for the series, at intervals not exceeding the manufacturer's published spacing for the orientation installed.
10.7.2 The bus manufacturer shall furnish the attachment hardware at the enclosure, the support brackets, and the hangers to the point of attachment to the structure, and the Contractor shall furnish the structural steel, the embedded anchors, the stanchions, and the trapeze framing between that point and the building structure or the outdoor foundation, as indicated on the bus duct routing plans and elevations.
10.7.3 Supports shall attach to the enclosure only at the points the manufacturer designates, and no support shall bear on a joint, a joint cover, an expansion provision, or a penetration fitting.
10.7.4 Supports shall be supported from the building structure or from a foundation designed for the run, and the Contractor shall confirm with the Engineer of Record that the structure at each support carries the weight per foot of the run and the seismic load where restraint is required, before the supports are installed.
10.7.5 Where a run is suspended, the supports shall allow the run to be leveled and aligned so that every joint closes square, and a run shall not be sprung into alignment at a joint.
10.7.6 An outdoor run shall be supported on stanchions or a structure that holds the enclosure clear of the grade and of any surface that ponds water, and the supports shall be of a material or finish suitable for the exposure, with no dissimilar-metal contact left between a support and an aluminum enclosure without an isolating washer or a coating.
10.7.7 The supports of an isolated-phase bus shall insulate the enclosures from the structure where the manufacturer's design requires it, so that enclosure current does not flow through the structure.

11 Identification

11.1 Nameplates, warning labels, and field-applied markings shall comply with Equipment LabelingElectrical Equipment LabelingResolves to the current adopted revision.sync/equipment-labeling for material, lettering, and attachment.
11.2 Each run shall carry a nameplate at each end stating the manufacturer's name, the bus type, the rated maximum voltage, the insulation level, the continuous current rating, the short-time and momentary withstand current ratings, the rated frequency, and the date of manufacture, as IEEE C37.23 requires, and the run designation on the one-line diagram.
11.3 Each run shall carry a marking at intervals not exceeding 50 ft along its length, and at each change of direction, stating the run designation and the system voltage, so that a run is identified at any point without tracing it to its source.
11.4 Each termination flange and each joint cover shall carry a phase identification at the conductors, so that the phase sequence is confirmed at any opening without reference to the far end.
11.5 Arc-flash warning labels shall be applied at each termination in accordance with NFPA 70 110.16 and NFPA 70E, with the values taken from the study performed under Arc Flash StudyArc-Flash Hazard AnalysisResolves to the current adopted revision.sync/arc-flash-study.
11.6 Where the run serves an emergency, legally required standby, or critical operations power system, it shall be marked as a component of that system in accordance with the article of NFPA 70 that governs the system, at the same intervals as the run designation.

12 Testing

12.1 Factory Design and Production Tests

12.1.1 The insulation level, the continuous current rating, the short-time withstand current rating, and the momentary withstand current rating of the bus series shall have been established by the design tests of IEEE C37.23, including the dielectric tests, the continuous current temperature-rise test, and the momentary and short-time withstand tests, and the manufacturer shall furnish the design test reports with the action submittals.
12.1.2 An outdoor enclosure shall have passed the rain test IEEE C37.23 prescribes for outdoor construction, and the design test reports shall include it.
12.1.3 The manufacturer shall perform the production tests of IEEE C37.23 on every section and fitting before shipment, including a power-frequency dielectric withstand test of every conductor to the enclosure and between conductors, and shall furnish a certified production test report for the sections and fittings furnished with the closeout submittals.
12.1.4 Factory test witnessing shall be as indicated in the datasheet.
Factory Tests Witnessedradio
○ Witnessed by the Owner's representative
○ Unwitnessed with a certified test report
12.1.5 Where witnessed testing is indicated, the manufacturer shall give the Owner not less than two weeks notice of test readiness, and the test procedure shall have been submitted and returned before the test date.
NOTE A witnessed test lets the Owner see the dielectric test applied to the sections that will ship and lets a representative check the flange fit against the equipment drawings before the run leaves the factory, and it commits a representative to a trip; a certified report records the same tests without the trip, and leaves a discrepancy to be found at field acceptance testing instead. A generator run or a run of a high voltage class is witnessed more often than a 600 V class transformer connection, so neither is distinctly the norm and the field asserts no default. (12.1.6)

12.2 Field Acceptance Tests

12.2.1 Field acceptance tests shall be performed on every run after installation is complete, after every joint has been made up and insulated where the conductors are insulated, after every cover has been closed, and before the run is energized, in accordance with ANSI/NETA ATS Section 7.4 and Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.sync/electrical-acceptance-testing, and shall include the tests indicated in the datasheet.
Field Acceptance Testscheckbox
☑ Visual and mechanical inspection including support spacing, restraint, covers, drains, breathers, and heaters
☑ Joint and termination torque verification against the manufacturer's values, with the record kept by location
☑ Insulation resistance of each conductor, phase-to-phase and phase-to-ground, for one minute
☑ Contact resistance across every joint, every flexible connector, and every termination with a low-resistance ohmmeter
☑ Phase sequence verification at every termination
☑ Enclosure ground path continuity from each end of every run to the other and to the equipment ground
☐ Space heater operation and thermostat setting on an outdoor run
12.2.2 Insulation resistance shall be measured for one minute at the test voltage ANSI/NETA ATS Table 100.1 assigns to the voltage class, with the run disconnected from the equipment at every termination, and a reading below the value that table states for the voltage class shall be investigated before the run is energized.
12.2.3 The overpotential test applied to each run after the insulation resistance test shall be as indicated in the datasheet.
Field Overpotential Testradio
○ AC overpotential test
○ DC overpotential test
○ No overpotential test, insulation resistance only
NOTE An AC overpotential test stresses the insulation and the air clearances the way service voltage does, finds a cracked insulator, a contaminated boot, or a foreign object left in the enclosure by breaking it down under test rather than in service, and needs a power-frequency test set whose capacity grows with the length of the run; a DC overpotential test needs a smaller set, which is why it is the test most often run on a long run, and stresses the insulation differently from service, so that a DC result is read against the DC value of the same table and not compared to an AC result. Insulation resistance alone finds gross contamination and a wet enclosure, reads through a cracked insulator, and is the only test a 600 V class run usually receives. Which a project wants depends on the voltage class, on the length of the run, and on the manufacturer's position on DC testing of the insulation furnished, and none of the three is distinctly the norm across the range this standard covers, so the field asserts no default. (12.2.4)
12.2.5 Where an overpotential test is selected, it shall be applied to each phase with the other phases and the enclosure grounded, at the test voltage and for the duration ANSI/NETA ATS Section 7.4 assigns to the test method and the voltage class, not exceeding 75% of the factory power-frequency withstand voltage of IEEE C37.23 for the class, and a run that fails shall not be retested until the cause has been found and corrected.
12.2.6 A joint whose contact resistance exceeds the manufacturer's published value, or exceeds the lowest joint of the same type on the same run by more than 50%, shall be opened, cleaned, remade with new hardware, and retested before the run is energized.
12.2.7 A run that fails a field acceptance test shall not be energized, the Contractor shall report the failure to the Engineer of Record within one working day with the measured values, and the cost of the correction and of every repeated test shall be borne by the Contractor.
12.2.8 Every run shall be included in the post-energization infrared survey performed under Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.sync/electrical-acceptance-testing, with every joint cover and termination cover scanned, and a connection showing a rise of more than 10 °C above its neighbors shall be reported and corrected.

13 Installation

13.1 Alignment and Assembly

13.1.1 Metal-enclosed bus shall be installed in accordance with NFPA 70 Article 368 Part IV and the manufacturer's installation instructions, and no section shall be joined until the equipment at each end has been set, anchored, and aligned to its final position.
13.1.2 Each run shall be assembled from the equipment flange outward in the sequence the manufacturer's instructions designate, with every section leveled and aligned so that each joint closes square without springing a section or an insulator, and a run shall not be used to pull the equipment at either end into alignment.
13.1.3 Before any joint is made up, the conductor contact surfaces shall be cleaned as the manufacturer directs for the plating furnished, and every shipping cover, desiccant, support block, and temporary protection shall be removed from the section.
13.1.4 Each joint and each termination shall be torqued to the manufacturer's published value with a calibrated torque tool, in the bolt sequence the instructions give, with the conical spring washers furnished, and the value applied shall be recorded in the joint torque record by location.
13.1.5 Where the conductors are insulated, each joint shall be insulated after it is torqued with the boot or the tape system the manufacturer furnishes, applied as the instructions direct, and no joint shall be left bare in an insulated run.
13.1.6 Before the enclosure is closed, the interior of every section shall be cleaned of debris, swarf, hardware, and tools, and every insulator shall be wiped clean and inspected, and the Contractor shall record the inspection by section.
13.1.7 Before a termination is bolted to the equipment, the Contractor shall confirm that the phase sequence of the bus conductors matches the phase sequence of the equipment bus, that the ground connection is in place, and that the two flanges align without forcing, and a mismatch shall be reported to the Engineer of Record before the connection is made.
13.1.8 Every joint cover, termination cover, drain screen, and breather shall be in place, and every space heater shall be energized, before the run is energized.

13.2 Clearances and Physical Protection

13.2.1 Metal-enclosed bus shall not be installed in a hoistway, in a hazardous classified location, or where it is subject to severe physical damage, and where the routing shown on the drawings passes through such a location the Contractor shall report the conflict to the Engineer of Record before the run is released for manufacture.
13.2.2 The run shall be located so that every joint cover is reached for inspection and infrared scanning from a floor, a platform, or a fixed ladder, and no run shall be routed through the working space or the dedicated electrical space of other equipment under NFPA 70 110.26 or 110.34.
13.2.3 An outdoor run shall be installed at a height, or within a fence, that keeps it out of reach of persons and of vehicles, and a run within reach of a vehicle shall be protected by bollards or a barrier shown on the bus duct routing plans and elevations.

14 Delivery, Storage, and Handling

14.1 Each section and fitting shall be delivered in the manufacturer's packaging with the section identification intact, with the joint contact surfaces and the conductor ends protected, and shall be inspected for shipping damage at receipt.
14.2 Sections shall be stored indoors in a clean, dry space where the temperature is held above the dew point, stacked as the manufacturer's instructions permit, and where indoor storage is not available they shall be stored under cover on blocking, off the ground, with the enclosure openings sealed, and protected from condensation, precipitation, dust, and physical damage.
14.3 Sections shall be handled and lifted in accordance with the manufacturer's instructions, by the lifting points or the enclosure as the manufacturer designates, and never by a joint, a cover, an insulator, or the exposed conductor at the end of a section.
14.4 A section or fitting that has been wetted, dropped, or bent in transit, in storage, or in handling shall be set aside, and shall be repaired or replaced as the manufacturer directs and as the Engineer of Record accepts in writing.
14.5 A section whose insulators or conductor insulation have absorbed moisture shall be dried as the manufacturer directs and shall pass the insulation resistance test before it is joined to the run.
NOTE An insulator that has taken up moisture in a damp warehouse, or a conductor insulation that holds a film of water, reads low on the first insulation resistance test and fails under an overpotential test at the first joint that holds water; the moisture is removed before the section is joined, not after the run is complete. (14.6)

15 Warranty

15.1 The manufacturer shall warrant each run, including every section, fitting, joint, insulator, flexible connector, and termination flange, against defects in materials and workmanship for the period indicated in the datasheet.
Manufacturer's Warranty Periodrange
years
1235
15.2 Where a warranty period is not selected in the datasheet, the manufacturer's standard warranty shall apply, and its term shall be stated in the product data.
15.3 The warranty period shall commence on the date indicated in the datasheet.
Warranty Commencementselect
Date of substantial completion
Date of energization
Date of shipment
NOTE Warranty commencement at shipment is the manufacturer's usual term, and it consumes the warranty while the sections sit in storage and the run is assembled; commencement at energization or substantial completion moves the coverage to the period the Owner is operating the run, and the manufacturer prices the added months into the bus. (15.4)
15.5 The warranty coverage scope shall be as indicated in the datasheet.
Warranty Coverage Scoperadio
○ Parts only
○ Parts and labor
15.6 The Contractor shall warrant the installation, including every joint made up in the field, every support, every restraint, and every termination, for the project warranty period.
15.7 A section, fitting, insulator, or joint replaced under warranty shall be warranted for the remainder of the original period or for one year from the date of replacement, whichever ends later, and the replacement shall not reduce the coverage of any other component in the run.

16 Spare Parts

16.1 The Contractor shall deliver the spare parts indicated in the datasheet to the Owner before the runs are accepted, and shall obtain a signed receipt for them.
Spare Parts to Be Furnishedcheckbox
☑ One complete joint hardware kit for every ten joints installed, and not fewer than two
☑ Two support insulators of each type installed
☐ One joint insulation boot or tape kit of each type installed, on an insulated run
☐ One set of joint cover gaskets for every ten joints installed, on an outdoor run
☐ Two breather filter elements of each type installed, on an outdoor run
☐ One space heater of each rating installed, on an outdoor run
☐ One pint of touch-up paint matching the finish
16.2 Spare parts shall be identical to and interchangeable with the installed parts, shall be delivered in their original packaging, and shall be labeled with the bus series, the rating, and the run designation they serve.
NOTE An insulator cracked by a dropped cover or a joint opened for an infrared finding is otherwise an outage that lasts for the manufacturer's lead time, and a joint remade with hardware from a supply house rather than from the kit is a joint outside the condition the run was rated under; the spares under this standard are the parts that let a joint be remade or an insulator replaced without either. (16.3)

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"Medium-Voltage Metal-Enclosed Bus." SynC Standards. Licensed under CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/). Source: https://synergyinconstruction.com/wiki/sync/medium-voltage-bus-duct — reference material only; not professional engineering advice and provided without warranty. Verify against governing codes and have a licensed professional review before use.