What’s the purpose of interlocking?
Switchgear interlocking is installed to protect both the equipment and the operator from dangerous situations caused by incorrect equipment operation. It can be categorized as operational interlocking and safety, or maintenance, interlocking. However interlocking logic is not always easy to understand and sometimes hard to design.

In details, it can be categorized as follows:
- Operational interlocking
This is concerned with the operational sequencing of disconnectors (both on and off load) when system connections are being reconfigured. This is usually achieved by ‘electrical-interlocking’ systems and generally applies to open-terminal substations. - Safety (maintenance) interlocking
This is concerned with the safe operation of switchgear, the provision of safe access to plant for maintenance purposes and the application of fixed earthing devices. It is usually achieved by mechanical-interlocking systems utilizing keys or, for distribution-voltage metal-clad switchgear, latches and bolts.
Note that one school of thought terms the former as ‘key interlocking’ and the latter as ‘mechanical interlocking’.
Premium Membership Required
This technical article/guide requires a Premium Membership. You can choose an annually based Plus, Pro, or Enterprise membership plan. Subscribe and enjoy studying specialized technical articles, online video courses, electrical engineering guides, and papers. With EEP’s premium membership, you get additional essence that enhances your knowledge and experience in low- medium- and high-voltage engineering fields.
Check out each plan’s benefits and choose the membership plan that works best for you or your organization.
Good to know 💥 – Get 50% discount on all video courses by purchasing Enterprise plan.
Log In »Purchase »
Related electrical guides & articles
Premium Membership

