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Description / Abstract:
These requirements cover automatic and non-automatic (manual)
transfer switches, operating at above 600 V ac, and intended for
use in ordinary locations to provide for power as follows:
a) Automatic transfer switches for use in emergency systems in
accordance with Articles 517- Health Care Facilities, 700-Emergency
Systems, 701-Legally Required Standby Systems, and 702-Optional
Standby Systems of the National Electrical Code, ANSI/NFPA 70 and
the National Fire Protection Association Standard for Health Care
Facilities, ANSI/NFPA 99.
b) Transfer switches for use in optional standby systems in
accordance with Article 702 of the National Electrical Code,
ANSI/NFPA 70.
c) In legally required standby systems in accordance with
Article 701 of the National Electrical Code, ANSI/NFPA 70.
d) Automatic transfer switches for use in accordance with the
National Fire Protection Association Standard for Centrifugal Fire
Pumps, ANSI/NFPA 20.
e) Non-Automatic transfer switches for use in accordance with
Articles 517-Health Care Facilities, and 702-Optional Standby
Systems of the National Electrical Code, ANSI/NFPA 70 and the
National Fire Protection Association Standard for Health Care
Facilities, ANSI/NFPA 99.
An automatic transfer switch for use in a legally required
stand-by system is identical to that used for an emergency
system.
These requirements cover transfer switch equipment rated greater
than 600 Volts, up to 15 kV.
These requirements cover transfer switches together with their
associated control devices including voltage sensing relays,
frequency sensing relays, time delay relays, and the like.
An automatic transfer switch as covered by these requirements is
a device that automatically transfers a common load from a normal
supply to an alternate supply in the event of failure of the normal
supply, and automatically returns the load to the normal supply
when the normal supply is restored. An automatic transfer switch
may be provided with a logic control circuit that inhibits
automatic operation of the device from either a normal to an
alternate supply, or from an alternate to a normal supply when the
switch reverts to automatic operation upon loss of power to the
load.
A non-automatic transfer switch as covered by these requirements
is a device, operated manually by a physical action, or
electrically by a remote control, for transferring a common load
between a normal and alternate supply.
A transfer switch may incorporate overcurrent protection for the
main power circuits.
These requirements only cover completely enclosed transfer
switches.
Transfer switches are rated in amperes and are considered to be
acceptable for total system transfer, which includes control of
motors, electric-heating loads, and transformer loads.