standards and guidelines for communication sites - Radio And ...

GENERATOR OUTPUT AND DERATING CONSIDERATIONS CHAPTER 6: POWER SOURCES
6.9.3 TRANSFER SWITCH
A transfer switch shall be installed to perform the switching between commercial power and standby
power. This switch is generally collocated with the site electrical service panel. In general, the following
considerations need to be observed:
• The switch shall have an ampere rating equal to or greater than the ampere rating of the circuits to
be transferred.
• The transfer switch is generally located inside a building; however, if the transfer switch is
enclosed in an approved watertight housing it may be located outside.
• Many areas require a disconnect switch in the feeder cabling between the generator and the transfer
switch. This facilitates generator servicing and provides an additional safety device to prevent AC
power backfeed into the commercial service.
• The neutral-ground bond shall not be made in the transfer switch.
• For domestic sites, installation of the transfer switch shall follow the manufacturer's recommended
installation guidelines as well as meet all applicable NFPA 70-2005, national, state and local codes.
Installations performed in non-domestic locations shall meet manufacturer's recommended
installation guidelines, as well as all applicable national and local codes.
• Surge suppression shall be installed. See Chapter 7, “Surge Protective Devices.”
6.9.4 ELECTRICAL WIRING CONSIDERATIONS
When designing the interconnection wiring between the generator, transfer switch, and site AC mains,
the following considerations shall be observed:
• There shall be two sets of circuit conductors run between the transfer switch and the generator. One
set shall be for low voltage control/alarm circuits and the second set for the electrical service. Each
set shall be installed within its own dedicated conduit/raceway.
• The control/alarm circuits shall not be installed within the same conduit or raceway as the
electrical service. (See NFPA 70-2005, Article 800.133 for additional information.)
• Conduits/raceways shall be sized and routed per the NFPA 70-2005, code (or equivalent in nondomestic
installations) and any other applicable national or local codes.
• A dedicated protected electrical circuit shall be provided at the generator for engine/battery heaters
and service equipment. If located outside, this circuit shall have ground fault protection.
6.9.5 INSTALLATION PLAN
Standby generator system installations shall be carefully planned and properly installed to ensure
proper operation for extended periods. All requirements for the proper location of the generator,
properly sized and positioned vents for the required airflow, fuel storage or supply, exhaust system
placement and electrical connections shall be reviewed by a qualified engineer or inspector to ensure
compliance with applicable NFPA 70-2005, national, state and local codes. In general, the following
considerations need to be observed:
6-40 68P81089E50-B 9/1/05