Snap-action switch S840 – Compact microswitch in a conventional design

Changeover contact with self-cleaning contacts and positive opening.

S840 k28 Snap-action switch S840 with flat lever and connections for flat plugs and soldering lugs
S840 b28 Snap-action switch S840 with flat lever and connections for flat plugs and soldering lugs
S840 v20 Snap-action switch S840 with roller lever and connections for flat plug
S840 b Snap-action switch S840 with pushbutton and screw terminals

The S840 snap-action switch is a high-quality microswitch in a conventional design. The mechanical positive opening ensures the opening of the switch, even if the contacts have been fused by a short circuit. The self-cleaning contacts also connect low voltages and currents safely and reliably. The S840 monitors the end positions or positions in safety applications.


Changeover contact, break contact or make contact

The standard design is a changeover contact with three connections. The switch is also available as break contact or make contact (with two connections).

Break contact with positive opening

If the break contacts fuse in the event of a short circuit, the catch spring can no longer open. It is nevertheless opened reliably via the lever of the positive opening. This is a positive opening as outlined in DIN EN 60947-5-1, annex K.

Self-cleaning contacts

The moving contact rubs against the fixed contact during every actuation. This removes corrosion and combustion residue and reduces contact resistance.

Reliable switching of low currents

With self-cleaning silver contacts, small currents can be connected reliably and frequently. In chemically aggressive environments and with low switching frequencies, we recommend gold contacts.

Dimensions 30 x 16.5 x 10.5 mm (L x H x W)

This is the maximum dimensions of the housing. The dimensions of the actuator and of the connections must be added. For all dimensions and drawings please refer to the following product catalogue:



Electrical Data
Contact configurationSPDT (Form C) snap-action switch with 3 terminals, positive opening operation, and wiping action
Conv. thermal current Ith EN609476 A at T = 85°C
Conv. thermal current Ith UL508---
Rated insulation voltage Ui EN60947250 V
Rated insulation voltage Ui UL508300 V
Pollution degree IEC 60947PD 3
Pollution degree UL508PD 3
Rated impulse withstand voltage Uimp2.5 kV
Utilization category IEC 60947AC-15, 230 VAC/1.5 A
Utilization category UL508240 V AC / 1 A (General Purpose), 240 V AC / 6 A (Resistive), 24 V DC / 6 A (Resistive), B300 - 240 V AC Std. pilot duty, B300 - 125 V AC Std. pilot duty
IP rating: contacts/terminalsIP40/IP00
Contact materialSilver or gold
Short-circuit protection6 A gG
Actuators, operating positions
ActuatorPush button, roller lever, plain lever, simulated roller lever
Free position16.0 ±0.1 (push button)
Operating position14.8 ±0.2 (push button)
Release position15.0 ±0.2 (push button)
Total positive opening travel13.6 (push button)
Total travel position< 13.5 (push button)
Movement differential (between operating and release position)0.2 (typical, push button)
Mechanical data
Front mount---
Ganging (side mount)yes, side mount
Vibration resistance5 g (10 … 500 Hz all directions, without aux. actuator at 0.1 ms max. opening time)
Shock resistance15 g, half sinus (without aux. actuator at 0.1 ms max. opening time)
Housing materialPC, green transparent
Mechanical endurance10 million cycles min.
Temperature range-40°C ... +85°C
NoteData valid for new switches with silver contacts

Related Downloads

Catalogue D40 – Snap-action switches S840
Single-break changeover, NC or NO contacts, positive opening operation and wiping action
Safety instructions snap-action switches
Snap-action switches S800 / S804 / S814 / S818 / S819 / S820 / S826 / S834 / S840 / S845 / S846 / S847 / S850 / S870 / S880 / S926 / S947 / S970
Safety instructions snap-action switches / Supplementary details
Snap-action switches S800 / S804 / S814 / S818 / S819 / S820 / S826 / S834 / S840 / S845 / S846 / S847 / S850 / S870 / S880 / S926 / S947 / S970
Manual SE-M
Snap-action switches S800 / S804 / S814 / S818 / S819 / S820 / S826 / S840 / S845 / S846 / S847 / S850 / S870 / S880 / S926 / S947 / S970 — Installation and Maintenance Instructions
/en/products/snap-action-switches/thank-you/Snap-action switch S840 Snap-action switches

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