Today, Wuxi Rihuan Sensor Technology Co., Ltd. will introduce to you how to select the "power-off state" of the security door lock? Is it power-off unlocking or power-off locking? 

In the selection of industrial safety door locks, there is a crucial but often overlooked issue: when the equipment is powered off, should the door lock automatically open or remain locked? 

There is no standard template for the answer to this question. It depends on the risk scenarios and safety goals of the equipment. If the wrong choice is made, it may only affect production efficiency, but in severe cases, it could endanger personnel safety or cause property damage. 

I. Definitions of the Two Modes

The safety door lock, based on its state after power failure, is mainly divided into two basic working modes: 

Power-off unlocking (Fail-Safe, also known as "Power-on Locking") 

Working principle: During normal operation, the lock body remains powered on, maintaining the locked state; when power is cut off, the lock tongue automatically retracts, and the door lock is opened. 

Safety concept: Prioritize ensuring the safety of personnel evacuation. In the event of power failure or malfunction, the door will automatically open to facilitate the emergency evacuation of personnel. 

Power-off locking (Fail-Secure, also known as "Power-on unlocking") 

Working principle: When operating normally, the lock body does not receive power and remains in the locked state; when powered on, the lock tongue retracts and the door lock is opened. 

Safety concept: Prioritize ensuring the safety of the area or property. In the event of power failure or malfunction, the door will automatically lock to prevent unauthorized personnel from entering. 

II. Core Differences Between the Two Modes

Comparison item Failed-Safe Mode Failed-Secure Mode

Normal state Continuous power supply, maintaining lock No power supply, maintaining lock

After power failure Door opens Door is locked

Priority of safety Safety for personnel evacuation Safety of the area/property

Typical scenarios Escape routes, emergency exits Equipment rooms, data centers, vaults

In the "Safe" of Failed-Safe Mode, it refers to the safety of people, not security (safety protection) - its design goal is to ensure that in cases of power failure and other faults, the door can fail in the most safe manner for people. 

III. Detailed Explanation of Applicable Scenarios

Scenarios for Power-Off Unlocking: 

Escape routes and fire doors: In case of power failure during emergencies such as fires, the doors will automatically open to ensure that people can evacuate quickly. In the building and fire safety regulations of most countries and regions, the doors on the escape routes must be designed with power-off unlocking functionality. 

Areas that require priority protection for personnel safety: such as safety exits in workshops, public passageways, etc. 

Power-off locking applicable scenarios: 

Equipment room, distribution room, control cabinet: After power outage, prevent unauthorized personnel from entering to avoid accidental operation or equipment damage. 

Data center, archives room, finance office: The doors will automatically lock when the power is cut off to prevent theft of property or leakage of data. 

Vault, high-value goods storage area: Remain locked after power outage to ensure the safety of assets. 

IV. Special Considerations in Industrial Safety

In the field of industrial mechanical safety, the situation is more complex than the simple "protecting people" or "protecting objects" dichotomy. According to EN ISO 14119 "Mechanical Safety - Interlock Devices Related to Protective Devices - Design and Selection Principles", if there is still dangerous overtravel movement (such as machines with rotating blades, swinging wheels, or robots) after the equipment receives a stop command, an interlock device with protective locking should be considered. 

At this point, it is necessary to distinguish between two types of protection requirements: 

Process protection: If the operator enters the hazardous area for a longer duration than the equipment's downtime, the "power-on locking principle" (power-on locking / power-off unlocking) can meet the process protection requirements. 

Personnel protection: If the operators can or must enter the equipment area, and the equipment itself has the risk of overtravel movement, then a safety protection lock that complies with EN ISO 13849-1 must be used. In this case, it is recommended to adopt the "power-off locking principle" (spring-activated locking, electromagnetic coil unlocking), that is, to lock with power off. 

In addition, there is a bistable principle: each time a rising edge signal is given to the coil to change the locking state, the current position will remain unchanged when the power is cut off - neither will it automatically open nor automatically lock. The bistable coil is very energy-efficient. The locking signal does not require continuous power supply, and even if the equipment is accidentally powered off, it can maintain the previous working state, preventing people from being accidentally locked in dangerous areas and avoiding being opened by accident. 

V. Selection Considerations

First, safety priority is the core criterion for judgment. Is this door an escape passage? In the event of power failure, must it be able to be opened (power failure unlocking) or must it be locked (power failure locking)? 

Secondly, when using power-off locking for escape routes, an emergency release device must be installed. If a power-off locking type door lock is to be used in the escape route, a mechanical release device (such as a handle or a glass-breaking button) must be provided to ensure that the door can be manually opened from the inside in an emergency. 

Thirdly, in the field of industrial safety, the principle of power-off locking (power-off locking) is given priority recommendation. For personnel entering high-risk equipment with potential risks, the power-off locking principle activates the lock through a spring and unlocks with an electromagnetic coil. It can automatically maintain the locked state during power-off, preventing personnel from accidentally entering. 

Fourth, refer to relevant safety standards. EN ISO 14119 provides clear classification and selection requirements for interlock devices. When selecting, it should be based on the risk assessment results of the equipment. 

VI. Summary

Power-off state Core principle One-sentence advice

Power-off unlocking (Fail-Safe) People priority Choose the escape route or emergency exit

Power-off locking (Fail-Secure) Property priority Choose the equipment room or data center

Bi-stable state Keep the current state Select this when power-off is necessary to maintain the current state

The selection of power-off states for security door locks essentially involves a trade-off between "people's escape safety" and "property safety in the area", while also considering industrial safety factors such as equipment overload risks. Before making the selection, ask yourself: When power-off occurs, am I more worried about people not being able to escape, or about the items being stolen? Is there still a risk of dangerous movement after the equipment stops running? 

Rihuan Sensor offers a full range of industrial security door locks, including power-off unlocking, power-off locking, and dual-stable states, etc., covering various working modes suitable for different risk levels and application scenarios. Welcome to follow Rihuan Sensor to obtain professional selection suggestions and technical support.