ASCO G7ATB / G962 — Main and Arcing Contact Adjustment

Adjustments · Arcing and main contacts

For the ASCO G7ATB / G962, from the ASCO service manual.

Procedure

1. Bypass, isolate, and pull out the transfer switch and verify that no electrical power is present.
2. Use the maintenance handle to open the contacts that will be adjusted (if not already open).
3. Remove the barriers: loosen only two round-head screws per barrier and slide the barrier away until the keyholes clear the screws.
4. Carefully remove the arc chutes: remove two long insulator nuts with a 5/8 in nutdriver and pull the arc chute outward.
5. A - Stationary Arcing Contact Alignment: loosen the two Sems screws, move the stationary contact left or right to center it under the movable arcing contact, then retighten to 66 in-lbs (5.5 ft-lbs);
6. B - Arcing Contact Lead Adjustment: install the adjusting hub and maintenance handle and close the contacts being checked.
7. For closed upper contacts, turn the maintenance handle clockwise 30 degrees until the AM hole is at 9 o'clock and fully insert the adjusting pin into hole AM.
8. For closed lower contacts, turn the maintenance handle counterclockwise 30 degrees until the AM hole is at 9 o'clock and fully insert the adjusting pin into hole AM.
9. Check that all nylon adjustment screws protrude 1/8 in through the far side of all movable arcing contacts; adjust with a blade screwdriver or 11/32 in nutdriver.
10. Verify that all main contacts are open approximately 1/8 in; if not, loosen the crank arm set screw with a 5/32 in hex key and turn the drive rod counterclockwise.
11. Insert the main contact shim gauge between the movable and stationary main contacts; it should fit finger tight. Turn the drive rod clockwise to decrease the gap, counterclockwise to increase it.
12. Turn each nylon adjustment screw until the arcing contacts just touch (no gap, no deflection); all arcing contacts on the same shaft should touch at approximately the same time.
13. Unpin the weight: insert the maintenance handle fully, grasp and hold it firmly, remove the adjusting pin, and gently allow the contacts to close.
14. Manually operate the transfer switch several times, then repeat the adjustment steps.
15. Carefully reinstall the arc chutes (gently tighten the insulator nuts until snug) and reinstall the barriers.

Source: ASCO service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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