MIL-HDBK-1025/10
b. Trip the circuit breaker open and discharge the stored-energy mechanism if
provided.
c. Check that protective interlocks are functioning to protect against closed-
position circuit breaker drawout.
d. Ensure that all crew members know you are racking out.
6.10.2 Circuit Breaker Maintenance. Access to switchgear terminals through
portholes in circuit breaker cells will be limited to the following:
a. When both sets of portholes in a cell are de-energized, that is line and load or
bus to bus.
b. After both are de-energized, the access to switchgear terminals through the
portholes will be permitted for cleaning, inspecting, and maintenance of terminals and
bushings.
c. Use an approved ground and test device for access to terminals. Such access
may be for application of protective grounds, phase identification on de-energized circuits,
and phasing tests on live circuits. The use of a ground and test device positively and easily
grounds the incoming cables and the switchgear bus. It also permits easy external
connection points to the bus or cable for testing.
6.10.3 Safety Precautions After Circuit Breaker Maintenance. After
providing required maintenance of the racked-out mechanism, the following precautions
will be taken as a minimum.
a. Check that the cubicle is free of foreign objects.
b. Check that control circuits are de-energized by pulling fuses on control circuits.
c. Ensure that the drawout mechanism is in the open position.
d. Ensure that all crew members are aware of that you are racking in.
e. Close the cubicle door before closing the circuit breaker
Network Protector Safety. A secondary network system provides a high
6.11
degree of continuity of service in heavy-load density areas. A grid of interconnecting low-
voltage cables is supplied by two or more medium-voltage feeders through transformers
having secondary network protectors. Network protectors are used in large buildings
with heavy loads since the loss of one point of supply does not cause loss of service.
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