産業用および安全用アプリケーションで一般的に使用される非常停止ボタンは、通常、ノーマルクローズ（NC）接点で設計されています。この構成により、フェイルセーフ機構が確保され、作動時に機械への電力を即座に遮断できるため、安全性と動作信頼性が向上します。
Comparison between NO contacts and NC contacts
| NO Contact | NC Contact | |
|---|---|---|
| Electrical Symbol |  |
 |
| Overview of the Switch Structure (Status Before Operation) |  |
 |
| Explanation |
|
|
| Use as an Emergency Stop Circuit | いいえ | はい |
| Behavior When Circuit Disconnection or Conduction Failure Occur | Current does not flow during operation. ->If used as an emergency stop circuit, machine does not stop when button is pressed. (Dangerous failure of the machine) |
Current does not flow even when the button is reset. ->Button reset cannot be recognized due to the structure of the circuit so the machine cannot be operated. (Safe failure of the machine) |
Emergency Stop Button Configuration
Emergency stop buttons typically employ normally closed (NC) contacts in their design, ensuring a default state where electrical contacts are engaged and current flows through the circuit. This configuration is crucial for maintaining operational safety in industrial settings. When activated, the button’s contacts open, immediately interrupting the power supply to connected machinery and triggering a rapid shutdown. International safety standards recommend this approach, as it provides a more reliable and responsive emergency stop mechanism compared to normally open (NO) configurations. The use of NC contacts in e-stop buttons is a widely adopted practice across various industries, prioritizing worker safety and equipment protection.
Immediate Response Mechanism
The rapid response capability of normally closed (NC) emergency stop buttons is a critical safety feature in industrial settings. When activated, these buttons instantly open the circuit, cutting power to machinery in milliseconds. This immediate interruption is crucial for preventing accidents and minimizing potential injuries in emergency situations. The swift transition from closed to open state ensures that even if the button is not fully pressed, it can still effectively halt operations. This design choice prioritizes worker safety by providing a near-instantaneous shutdown mechanism, making NC contacts the preferred configuration for emergency stop systems across various industries.
Fail-Safe Safety Design
The fail-safe design of normally closed (NC) emergency stop buttons provides an additional layer of safety in industrial settings. If a fault occurs in the circuit, such as a disconnection or wire break, the NC configuration ensures that the equipment will automatically stop operating. This inherent safety feature prevents machinery from running when it should not, reducing the risk of accidents or equipment damage. The fail-safe mechanism is particularly valuable in situations where continuous operation could pose a danger, as it defaults to a safe state even in the event of system failures or power loss. This design philosophy aligns with international safety standards and best practices for emergency stop systems, prioritizing worker protection and equipment integrity in potentially hazardous environments.
Operational Reliability Benefits
The normally closed configuration of emergency stop buttons enhances operational reliability in several ways. By maintaining a closed circuit during normal operation, these buttons can detect and respond to partial activations, ensuring safety even if not fully pressed. This design also allows for continuous monitoring of the circuit’s integrity, immediately triggering a shutdown if any faults or disconnections occur. Additionally, the NC setup reduces the likelihood of false alarms or unintended activations, as it requires a deliberate action to break the circuit. These features collectively contribute to a more robust and dependable emergency stop system, crucial for maintaining safety standards in industrial environments where quick and reliable responses are essential.
