KSD9700/BK05-BB1D Metallic Shell Temperature Control Switch (55°C NC, 10A 250V)

The KSD9700/BK05-BB1D is a Normally Closed (NC) switch. This means the electrical contacts are closed, allowing current to flow, when the temperature is below its 55°C setpoint. When the temperature rises to 55°C, the internal bimetallic disc snaps open, breaking the circuit to protect your equipment. It does not automatically reset; the contacts remain open until the device cools down sufficiently.

Yes, it can be used as a safety cut-off. It is rated for 10A at 250V, which is suitable for directly interrupting the power line to many heating elements, motors, or transformers. For control applications, it is typically wired in series with the load. Ensure your load's operating current does not exceed the 10A rating to prevent contact welding or failure.

Installation is straightforward. Mount the metallic sensing head directly onto or near the component you wish to monitor (e.g., motor housing, transformer core). Connect its two pre-attached 7cm lead wires in series with the power line of the device being protected. Ensure good thermal contact with the monitored surface for accurate temperature response. The switch is not polarity-sensitive.

Standard bimetallic thermal switches like this typically have an operating tolerance of ±3°C to ±5°C around the stated 55°C setpoint. The reset differential—the temperature at which the contacts close again after tripping—is usually 10°C to 20°C below the trip point. Therefore, after opening at 55°C, it may reset when the temperature falls to approximately 35-45°C.