Switchgear interlocking

Originally used in high voltage applications, mechanical interlocks have been adapted for use on medium and low voltage switchgear.

Fortress Systems manufactures and supplies the Castell, H31 Fortress, and Ronis range of mechanical interlocks.

Interlocks are mounted to the switchgear to lock in either the open or closed position, or in some cases both. Once the switchgear has been operated a key is released and taken to the next interlock in the sequence. These interlock systems are simple, robust, and foolproof, and the status of the key provides tangible proof of the operational status of the switchgear. The simplicity of design ensures that interlocks can be retrofitted to almost all types of switchgear, irrespective of size and rating.

The most common application is to prevent the paralleling of incoming power supplies, and this is achieved by interlocking the bus tie(s) with the incoming feeder switches, eg, in the case of two feeders and a single bus tie, a mechanical interlock is fitted to each switch - three in total - to lock the switch in the open position when the key is freed. Each interlock has the same key combination. Only two keys are used, ensuring that the bus tie switch cannot be closed when both feeder switches are closed.

By using the same principle it is possible to ensure that earth switches are closed only after the isolator has been opened. In this case two locks, with the same key combination, and a single key are used.