What is the Normally Open (NO) Thermostat Switch KSD301?

The Thermostat Switch KSD301 bimetallic disc operates in a Normally Open (NO) configuration. This means the circuit is initially open (disconnected) at normal temperatures. When the temperature rises to a predefined threshold, the bimetallic disc bends, closing the circuit and allowing current flow.

Normally open THERM-O-DISC T-O-D THERMAL LIMIT SWITCH L160-40F 60TX01

UL/CUL KSD301 Shutoff Thermostat,Normally Open NO Bimetal Snap Disc 125V 16A Auto Reset

uxcell KSD301 Thermostat 40°C/104°F 10A Normally Open N.O Adjust Snap Disc Temperature Switch

IO. Core Features
‌Operation Principle‌
When the temperature rises to the set value, the contact automatically connects the circuit; when the temperature drops to the reset value, the contact automatically disconnects the circuit, which is the opposite of the normally closed type (disconnected when the temperature rises and connected when the temperature drops).

The bimetallic strip is heated and deformed to trigger the mechanism to achieve fast switching.

‌Technical Parameters‌
‌Electrical Specifications‌:
Tensione nominale: AC 250V (carico resistivo) or AC 125V (UL standard)
Corrente nominale: 5A/10A/15A (carico resistivo)
‌Temperature performance‌:
Action range: 0℃~300℃ (personalizzabile), accuracy ±2℃~±10℃17
Reset and action temperature difference: 8℃~100℃ (adjustable)
‌Mechanical characteristics‌:
Resistenza di contatto: ≤50 mΩ, insulation resistance: ≥100MΩ13
Forza elettrica: AC 1800V/1min without breakdown
Vita utile: ≥100,000 times17 (some models up to 150,000 times2)

‌Physical characteristics‌
Livello di protezione: IP00 (no dust and water resistance)
Metodo di cablaggio: plug-in terminal 250# O 187# (angle 0°~90° optional)
Metodo di installazione: supports various structures such as movable ring, flat ring, aluminum cover with holes, ecc.

Normally Open State:
The KSD301 is designed to have its contacts in an open state when the surrounding temperature is below the specified operating temperature. This means the circuit connected to the KSD301 is broken, preventing current flow.

Temperature Trigger:
All'aumentare della temperatura, the bimetallic disc (made of two different metals bonded together) responds to the temperature change. The two metals expand at different rates, causing the disc to bend.

Circuit Closure:
When the temperature reaches the set point, the disc bends enough to close the circuit, establishing a connection between the contacts. This allows current to flow through the circuit.

Ripristino automatico:
Once the temperature drops below a certain level, the bimetallic disc returns to its original shape, opening the circuit again and cutting off the current flow. This is an automatic reset feature.
In essence, the KSD301 is used as a thermal switch to control current flow based on temperature, acting as a temperature sensor and protector for various applications.

Ii. Scenari di applicazione
‌ Hhousehold Appliances‌: distributori d'acqua, electric thermos, forni a microonde, cabine di disinfezione, Riscaldatori elettrici, macchine per il caffè, ecc.
‌Industrial equipment‌: motor overheat protection, rectifier equipment, macchine plastificatrici, car heated seats, etc.57.

III. Detection method (determine whether it is normally open)
‌Multimeter detection‌:
A temperatura ambiente (‌below the action temperature‌): the resistance of the two pins should be infinite (open circuit).
After heating (‌above the action temperature‌): the resistance value drops to ‌tens of ohms‌ (open circuit).
‌Marking distinction‌: The product body is usually marked with “NO” (Normalmente aperto) O “Normalmente aperto”.

IV. Product advantages
Fast response speed, clean contact action without arcing57;
Precisione di controllo ad alta temperatura, strong reliability7;
Compact structure, strong adaptability17.

⚠️ Note: The actual selection needs to confirm the specific temperature threshold (such as 85℃, 95℃, ecc.) and the reset temperature difference. The parameters of different models may vary.