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26 20 00 LOW-VOLTAGE ELECTRICAL DISTRIBUTION

.01 General
  1. Services (480V and below)
    1. Design shall include single-line diagram(s) from the Service Entrance equipment through to each branch circuit panel or large load.  Show all breakers through any panelboard mains.  Riser format is preferable for clarity.
    2. Equipment shall be fully rated, series rated is not acceptable.
    3. Provide a set of “as-built” drawings stored in the main electrical room.  Storage shall be in a transparent PVC tube with a removable end.  The tube shall be mounted to the wall horizontally.  Tube shall be sized appropriately for drawings that will be placed inside.  Label tube appropriately.
    4. Provide 30”x42”, laminated copy of the single-line diagram(s) adjacent to the service entrance equipment.  Mount in aluminum frame under plexi-glass.  Smaller size may be acceptable depending on the project, contact Engineering Services for direction.
    5. Consider using a SPD (surge protective device) on lighting/appliance panels.  Review this with Engineering Services.
    6. Contact Engineering Services for a list of acceptable equipment manufacturers.
    7. All busing and wiring is to be copper.  Specify that all field-replaceable lugs are to be copper (switchgear, switchboards, and panelboards), no aluminum is allowed due to failure from over-torquing.
    8. Design professional shall perform and submit voltage drop and short circuit studies.  Voltage drop study shall size feeders utilizing a load equal to 80% of the overcurrent device rating.  Engineer shall size feeders for a maximum 2% voltage drop.  Engineer shall also provide information on each Panelboard advising the contractor as to the maximum length of a #12 AWG and #10 AWG branch circuit feeding a 12 A load to maintain no more than an additional 3% voltage drop.  Short circuit study shall utilize the feeder sizes as determined by the voltage drop study.
    9. Coordinate the requirement for panic hardware on door(s) exiting the main electrical room with the architect.  When required, provide true panic bar setup to allow egress without use of hands, in case of electrical burns.
    10. Indicating lamps on any equipment shall be LED.
    11. When temporary power for a construction site is fed from a building with ground fault protection, the temporary power feeder shall be fed from a breaker with ground fault detection.
    12. Electronic trip units with display must have integral power supply.  Main/tie/main gear shall have dual power supplies with interconnection in tie section.  Power supply must be multi-tap, capable of running on 120/240 VAC, and 48/24 VDC.
    13.   All normal circuit breakers of frame sizes specified with a rating  ≥ 100 225 amperes Amperes up to 400 amperes shall incorporate adjustable magnetic trip.  Breakers 400 amperes and larger shall incorporate electronic trip units with functions as determined by the coordination study and as required by NEC.  All breakers on the emergency branch (NEC Article 700 loads) rated ≥ 60 Amperes shall incorporate electronic trip units to satisfy code required selective coordination. All breakers on the optional standby branch (NEC 702) rated ≥ 200A shall incorporate electronic trip units. Breakers in main electrical equipment shall also have integral cause of trip indication.  Trip units that utilize battery backup, shall have field replaceable batteries.  Provide 20% spare batteries as well as full function secondary injection portable test set.  utilize battery backup, shall have field replaceable batteries.  Provide 20% spare batteries as well as full function secondary injection portable test set. 
    14. Provide Coordination Study, per the Engineering Power Studies section.
    15. Specify that the Engineering Power Studies be submitted to Engineering Services prior to receiving final approval of the electrical distribution equipment shop drawings and prior to release of equipment for manufacture.
    16. Require nameplate on each upright section, both front and rear, for switchgear and switchboard assemblies.
    17. Require IR camera windows on each rear section of switchgear, confirm scope with Engineering Services.
    18. Minimum AIC ratings for electrical equipment shall be 22,000 AIC for less than or equal to 240VAC and 42,000 AIC for greater than 240VAC. The AIC ratings for electrical equipment shall be verified by the Power Study, upsizing of AIC rating may be required.  The Design Professional shall bare responsibility to ensure the proper AIC rating is chosen for a specific piece of equipment.
  2. Service Entrance Equipment
    1. Where Unit Substation is approved, provide secondary main overcurrent protection. 
    2. Ground fault protection – provide where required by the National Electric Code.  When the main circuit breaker has ground fault protection, all second level breakers must also have ground fault protection.  When a third level breaker equals or exceeds 400 amps, consider additional ground fault protection.  Consult with Engineering Services.  Properly interlock all levels of ground fault protection to insure tripping at the lowest possible level and verify on the Coordination Study required under the Engineering Power Studies section.
      1. Annunciate breakers with ground fault trip capability for a ground fault trip and include a ground fault trip indicator.
      2. 208V systems shall not have ground fault breakers in the secondary distribution system except as required by code.
    3. Designs for PSU shall strive to provide the lowest possible arc flash incident energy.  Contact Engineering Services to determine whether to specify ARM (Arch Flash Reduction  Mode) system on any Project.  ARM shall utilize either arc flash light/current sensing system or separate arc reduction circuitry switch for use during maintenance and inspection of the service entrance equipment.  Alternative arc flash reduction methods will be considered.  When utilized, the ARM switch system shall adjust the trip curve of the breaker relay. Systems utilizing “zone-interlock” exclusively are not acceptable.  ARM system shall have remote lockable switch(es) on the front of the gear to initiate this setting with separate blue LED light(s) for notification.  When this circuitry is provided, monitor the activation via CCS (Central Control System), per the BAS Specification.  Require dual Arc Flash stickers to meet NFPA 70E, refer to Engineering Power Studies section of the standards.  Manufacturer representative shall provide letter stating that they have visited the site and confirmed that the stickers have been applied in appropriate locations, per the Study.
    4. Refer to 26 27 13 - Electricity Metering for requirements.
    5. Refer to 26 35 33 - Power Factor Correction Equipment for requirements.
    6. Refer to 26 43 13 - Surge Protective Devices for Low-Voltage Electrical Power Circuits for SPD requirements.

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