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Interlock Application - Prevent Paralleling of Lines

Scheme # 23
To prevent paralleling incoming primary sources, lines 1 and 2, through the primary tie bus disconnect or the secondary tie bus breaker. To prevent operation (open or closed) of the disconnects under load. Permits one power source to supply both loads through either the primary or secondary tie bus.

Under normal conditions breakers A and B are closed, breaker C is locked open, disconnects D and E are locked closed, and tie disconnect T is locked open. Keys A-1 are held in L-O interlock on breaker A and L-C interlock on primary tie bus disconnect T. Keys A-2 are held in L-O interlocks on disconnects D and E. Keys A-3 are held in L-O interlock on breaker B and L-C interlock on primary tie bus disconnect T. Keys A-4 (free keys) are shown in removable position in the L-C interlocks on disconnects D and E. Keys A-5 are held in L-O interlocks on breakers A and B.

To transfer load No. 1 from line 1 to line 2 through primary bus tie disconnect T, proceed as follows:

Reverse procedure to restore service to line 1. Load No. 2 can be supplied from No. 1 through the primary bus tie in a similar manner.

To transfer load No. 1 from line 1 to line 2 through the secondary tie breaker C, proceed as follows:

Reverse procedure to restore service on line 1. Load No. 2 can be supplied from line No. 1 through the secondary tie breaker C in a similar manner.

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Scheme # 27 Scheme # 28
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Scheme # 33 Scheme # 34
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Scheme # 35A
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