Nevion 3GHD256256L - Manual (Page 12)

3GHD256256L / SD256256L Rev. E
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There are also two Power fail alarm relay contacts on the rear side of the frame; see
Chapters 2.2 and 2.5 for details. Each installed PSU module has a separate pair of contacts.
The relay contact is normally open, and the contact closes on power failure.
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The PSU module A alarm is formed by contact between Pin 3 and Pin 6 (Green pair)
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The PSU module B alarm is formed by contact between Pin 1 and Pin 2 (Orange pair)