Check the Permissives First
Most vacuum circuit breakers will not close unless several conditions are satisfied. Before suspecting a component failure, confirm each permissive:
- The closing spring is fully charged and the charged indicator is showing.
- The breaker is fully in the service or test position, not part way through racking.
- Any mechanical or electrical interlocks are satisfied, including earth switch and door interlocks.
- No lockout or anti-pumping condition is active.
Closing Circuit and Coil
If the permissives are met, check that control voltage reaches the closing coil when the close command is given. A failed closing coil, a loose terminal, or a faulty control switch can all stop the breaker closing. Compare coil resistance with the datasheet, and see our comparison of trip and closing coils.
Spring Charging
If the spring will not charge, look at the spring charging motor, its supply, and its limit switches. A worn motor, dirty commutator, or failed limit switch is a frequent culprit.
Mechanical Causes
Stiff linkages, dry bearings, or a worn latch can prevent the mechanism from completing its closing stroke even when everything electrical is healthy. Lubrication and mechanism inspection per the manufacturer schedule are the fix.
For replacement motors, coils and limit switches, see our VCB spares or send an RFQ with your breaker model.