Safety Switches

Sample Applications

Sample Application—1

To prevent two devices from being closed simultaneously.

Two devices are shown in Figure 1. In operation they are not closed at the same time. With the interlocks arranged as shown only one key is required in the interlocking system. Both devices are shown open, therefore, the key is free. To close any one device the key is inserted and turned in that particular lock, the key is held in this lock until the device is again locked open. This simple interlocking sequence lends itself to a multitude of applications. The procedure is the same for two devices, neither of which is to be opened at the same time.

Sample Application—2

To prevent opening of switch A when circuit breaker B is closed.

Switch A and circuit breaker B are in closed position. Key A-1 is held in circuit breaker B interlock.

1.	Open circuit breaker.

2.	Turn key A-1 in L-O-R interlock on circuit breaker B to lock open. Key A-1 is now free.

3.	Insert key A-1 in L-C-R interlock on switch A and turn to unlock.

4.	Open switch A. Key A-1 is now held. Reverse sequence to restore service.

Sample Application—3

To prevent operation of switch A when circuit breaker B is closed. Permits re-closing of circuit breaker for servicing when switch is locked open.

Switch A and circuit breaker B are in closed position. Key A-1 is held in circuit breaker interlock.

5.	Open circuit breaker.

6.	Turn key A-1 in L-O-R interlock on circuit breaker B to lock open. Key A-1 is now free.

7.	Insert key A-1 in L-O-C-R interlock on switch A and turn to unlock.

8.	Open switch A.

9.	Turn key A-1 in L-O-C-R interlock on switch A to lock open. Key A-1 is now free.

10.	Return key A-1 to circuit breaker interlock and unlock for operation during servicing period.

Reverse sequence to restore service.

Sample Application—4 (Main-Tie-Main)

To prevent paralleling of lines A and B.—Two loads, fed from either source.

Circuit breaker A is closed to supply load M. Circuit breaker B is closed to supply load N. Tie-circuit breaker C is open. Keys A-1 are held in interlocks on both circuit breakers A and B. Tie-circuit breaker C cannot be closed unless either A or B is locked open.

To transfer load N to circuit breaker A, proceed as follows:

1.	Open circuit breaker B.

2.	Turn key A-1 in L-O-R interlock on circuit breaker B to lock open. Key A-1 is now free.

3.	Insert Key A-1 in L-O-R interlock on tie-circuit breaker C and turn to unlock. Key A-1 is now held.

4.	Close tie-circuit breaker C.

5.	Reverse sequence to restore service.

6.	Load M can be supplied through circuit breaker B in a similar manner.

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