ST01 B U4 Thermal protector

Power class: 1,6 A to 7,5 A

Type series: ST01

normally open
resets automatically
with connector cables
blue epoxy resin insulation
ST01 U4_1
ST01 U4_2

ST01 B U4 Thermal protector

Main parts

1) Ceramic cover plate 2) stationary silver contact 3)  spring disc 4) movable contact 5) Conductive housing 6) bimetal disc


Stationary silver contact are riveted with ceramic cover plate. The movable contact are welded to the spring disc, which is in the shape of a cross, and the four feet are connected to the bottom of the housing. The inner hole of the bimetal disc is placed on the spring disc through the movable contact. The current pass through the stationary silver contact to the movable contact, and then connects the conductive housing through spring discs to form a loop.


When the circuit is normal, the movable contact is in close contact with the stationary silver contact under the pre-pressure of the spring disc. When the rated operating temperature is reached, the bimetal disc is deformed by heat, snaps into its inverted position and pushes the spring disc downwards. The contact is abruptly opened and the temperature rise of the device to be protected is disrupted.

After the circuit is disconnected, the ambient temperature begins to fall.  When it reaches the defined reset temperature, the bimetal disc and the spring disc snaps back into its start position,  the movable contact and the stationary  silver  contact  will  close  again, and the circuit returns to the conduction state.


Nominal switching temperature (NST) in 5°C
60 °C - 180 °C
Tolerance (standard)
Reverse switch temperature (RST) tolerance
≥ 35 °C (≤ 80°C NST)
-30K±15K (≥ 85°C ≤ 180° C NST)
Length of the insulation cap
Resistance to impregnation
Suitable for installation in protection class
Pressure resistance to the switch housing
Standard connection
0.33 mm² / AWG22
Insulation voltage
1.5 kV
Available approvals
Operating voltage range AC/DC
up until 500 V AC / 14 V DC
Rated voltage AC
250 V(VDE)
277 V(UL)
Rated current AC cos ϕ = 1.0 /cycles
2.5A / 10,000
Max. switching current AC cos ϕ = 1.0 /cycles
6.3 A / 3,000
7.5 A / 300
Rated current AC cos ϕ = 0.6 /cycles
1.6 A / 10,000
Rated voltage DC
12.0 V
Max. switching current DC /cycles
40.0 A / 5,000
Total bounce time
< 1 ms
Contact resistance
≤ 50 mΩ
Vibration resistance at 10 ... 60 Hz
100 m/s²



Sales:Don Qu

Phone:+86 183 5813 1344

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