Interlocking between different switchgear apparatus and enclosure access covers and doors enhances personnel
safety, as well as improving operational convenience.
Interlocking uses electrical and mechanical methods or a combination of both.
- For metal-enclosed switchgear with removable switching apparatus:
- the switching device must be in the open position before it can be withdrawn
- the switching device can only be operated in the positive service or test position
- the switching device cannot be closed unless the auxiliary control circuits required to open the switch are connected.
- For metal-enclosed switchgear with disconnectors:
- a disconnector cannot be operated under conditions other than those for which it is intended to be used
- a disconnector cannot be operated unless the main switching device is open
- operation of a main switching device is prevented unless its associated disconnector is in a positive service, test or earth position.
- disconnectors providing isolation for maintenance and servicing must have a locking facility.
The figure shows a common switchgear arrangement for a medium voltage. This switchgear arrangement uses three separate interlocking methods.