D. If internal flashover occurs, isolate the phases and test each one independently to
identify the defective interrupter. Any defective pole assembly must be replaced prior
to the breaker being in service.
5. Contact Resistance: Measure contact resistance with suitable equipment rated not less
than 100 A. The value should not exceed 150 micro ohms.
9.1 Replacement of Vacuum Interrupter (See Figures 3-7)
With R-MAG breaker in the open position:
1. Remove 1/2 x 12 bolt (H) through the Contact Block (C) on moving end of the Vacuum
Interrupter (VI).
2. Loosen Hex (F) nut one turn on Bolt stem (E) attached on moving end of the VI.
3. Remove X-washers and pins on Triangle Bell crank at Pivot Bracket and Bolt Stem.
4. Swing Pull Rod (A) away and remove Bolt Stem ensuring Hex nut remains in position.
5. Wedge large screwdriver tip to spread gap on the Contact Block. (This will allow the
threaded moving end of the VI to easily spin out of the Contact Block in step 7.)
6. Remove bus at fixed end of the VI.
7. Rotate VI counterclockwise (CCW) until it is completely free of the Contact Block.
8. Install new VI, carefully ensuring the VI spins in to the Contact Block without any
resistance. The bellows portion of the VI is very sensitive to torsion forces. Ensure VI is
completely against the bus at the moving end of the VI and the VI stem is flush with
Contact Block. Remove screwdriver used to spread Contact Block.
9. Replace the bus on fixed end of the VI.
10. Replace Bolt Stem to location one turn from tight, with pin hole horizontal.
11. Replace Pin and X-washer at Pivot Bracket.
12. Refer to 9.2 for adjustment instructions prior to replacing the pin through Bell Cranks and
Bolt Stem.
Page 9
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