This scheme is used to prevent the operation of the non-load break disconnect switch while the breaker is closed and preventing access to the breaker enclosure with the switches closed.
Initial Condition: the line feeds the load through switch #1 and breaker #1 and switch #2. Breaker #1 is closed with key "A" captive in its key interlock. Switch #1 is locked closed with no key present in its LC position key interlock while its LO position key interlock has a "B" key captive. Switch #2 is locked closed with no key present in its LC position key interlock while its LO position key interlock has "D" and "A" keys captive. The breaker enclosure is locked closed with no interlock key present.
Opening the Non-load break disconnect switch and gaining access to the breaker compartment: open and lock breaker #1 thereby removing the "A" key. Use the "A" key to unlock and open switch #1. Lock switch #1 in the open position thereby releasing the "B" key. Use the "B" key to unlock and open switch #2. Lock switch #2 open thereby releasing the "D" and "A" keys. The "A" key may be held by the operator as evidence of the switching operation or may be used to unlock the breaker for servicing or testing. The "D" key may be used to gain access to the breaker enclosure. Reverse to restore the initial condition.
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