“Normally open” and “normally closed” describe the brake’s state when no power is applied. A normally closed brake is engaged by default and requires power to release—this is the common fail-safe configuration (spring-applied, power-released). A normally open brake is released by default and requires power to engage.
In safety-critical applications like hoists and cranes, normally closed (fail-safe) brakes are preferred because a power loss results in braking, not free movement. Normally open brakes may be used in controlled process equipment where unintended stopping is dangerous or where braking is commanded only during operation and power reliability is high.
When evaluating “normal state,” always consider the complete system behavior during faults: power loss, broken cables, valve failures, and control system errors. Also confirm whether the brake is intended for dynamic stopping or holding. In many cases, the term “normally closed” is used interchangeably with “fail-safe,” but verify the actual mechanical design (springs applying force) rather than relying on labels.
