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Scheme A

Scheme A This scheme is used to prevent two Mains or a Generator and a Main or two Generators from being tied together through their own associated switch or breaker. This scheme prevents two switches or breakers from being closed simultaneously.

Initial Conditions: The load is fed from line #1 through breaker #1 which is normally closed with its respective interlock key "A" captive. Breaker #2 is locked open with no interlock key present.

Switching the load to line 2 through breaker 2: Open breaker #1 and lock thereby releasing the "A" key. Use the "A" key to unlock and close breaker #2. Reverse to restore the initial condition.


  1. Open switch or breaker #1
  2. Lock open by extending locking bolt - this releases key "A"
  3. Insert key "A" into lock on breaker #2
  4. Unlock and retract locking bolt - this allows breaker #2 to be closed
  5. Reverse above procedure to restore to original condition

Additional Schemes:
A / A1 / B / B1 / C / D / E / F / G / H /
H1 / H2 / K / L / M / N / O / P / R / U.P.S. System / Capacitor Bank Access Scheme

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