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Centric 3x480 Vac, Installation Guide, rel. 2.2
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10. Using the UPS with a generator
10.1
The Automatic Transfer Switch (ATS)
At many sites a generator is used as a reserve source for feeding the UPS during mains power failure. In
such cases, the switching between the two sources (the mains and the generator) is performed by an
Automatic Transfer Switch (ATS). Because these two sources are not usually synchronized, switching
between them requires an interval of at least 10 seconds.
Figure 77 illustrates the timing factors involved when using an ATS. For proper functioning of the UPS, the
values used for T3 and T4 must be greater than 10 seconds. The optimum delay times can be revealed
with a little testing, and may vary from site to site, depending on the UPS, on the loads, and on the
particular ATS being used.
Figure 77: Timing variables when using a generator and an ATS
