Page 53 - Uninterruptible Power Supplies

Interconnecting the Standby and Normal Supplies
Interconnecting the Standby and Normal Supplies 51

closed contact of a load shedding relay. Aload shedding signal energizes
the relay thus releasing the contactor which remains open until the
load shedding signal is removed. A circuit breaker may be used in place
of the contactor. For a large site using many load shedding relays and
long runs of telephone type cable, consideration must be given to the
relay operating current and the volt drop in the telephone-type cable.

Figures 2.1 and 2.2 show typical methods of connecting single gener-
ating sets, Fig. 2.1 applies to a small set using electrically and mechan-
ically interlocked changeover contactors or circuit breakers, and Fig. 2.2
applies to a set using electrically interlocked circuit breakers.

Figure 2.1 Single-line diagram showing a typical method of connect-
ing a small single set using changeover contactors.

Figure 2.2 Single-line diagram and switching status
table showing a typical method of connecting a single set
using electrically interlocked circuit breakers.

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