Snap-action vs shorting bar pushbuttons: Contact design choices in the OTTO P9 Series

When specifying a momentary pushbutton, most engineers are already familiar with the external choices. Button profile, mounting method, sealing level, and termination style are typically resolved early and documented clearly.

What is less often written down is how the internal contact mechanism influences behaviour at the point of actuation. Snap-action and shorting bar designs are both widely used, but they behave differently under load, provide different operator feedback, and suit different switching duties.

Pushbuttons are often standardised early in a design or carried forward from previous builds. Once selected, they tend to disappear into the background of a panel bill of materials. When behaviour differs between variants, however, the internal contact mechanism becomes relevant again, particularly during review, substitution, or troubleshooting.

The OTTO P9 Series provides a useful reference point because it offers both snap-action and shorting bar contact designs within the same pushbutton family. This makes it possible to treat the contact mechanism itself as a deliberate design choice rather than an incidental detail.

Momentary action as a design baseline

All P9 Dome series pushbutton switches are momentary action devices. The contacts change state only while the button is actuated and return to their normal position when released.

Within that common operating principle, the P9 Series includes multiple internal contact arrangements. These arrangements influence how the contact transitions occur and how the switch behaves electrically and mechanically during operation.

Snap-action contact design in practice

Selecting a snap-action contact design introduces a defined transfer point between operator movement and contact transition. In the P9 Series, snap-action models use a double-break mechanism that transfers the contacts rapidly once the actuation threshold is reached.

In practice, this produces two outcomes that are relevant during specification. The contact transition is decisive, limiting the duration of intermediate states during actuation. The mechanism also provides positive tactile feedback, giving the operator a clear physical indication of when the switch has actuated.

Within the P9 Series, snap-action models are rated for resistive and inductive loads within the published limits. Electrical life varies with load, ranging from up to one million operations at lower loads to a minimum of 25,000 operations at full rated load of 5 amperes resistive or 3 amperes inductive. These values define the operating boundaries of the snap-action mechanism.

Snap-action contacts are also specified as withstanding extreme shock and vibration. This characteristic relates to contact transfer stability.

Shorting bar contact design and low-level switching

Shorting bar contact designs follow a different mechanical and electrical logic. In the P9 Series, shorting bar models do not incorporate a snap mechanism. Contact movement follows the mechanical travel of the button rather than transferring at a defined snap point.

This becomes relevant for low-level switching duties. Shorting bar models in the P9 Series are rated at 10 milliamperes at 5 volts DC and are specified with an electrical life of up to one million operations under these conditions.

Because the design does not provide a snap transition, shorting bar models do not offer tactile feedback at the point of contact transfer. Instead, they rely on stable contact pressure and contact construction to maintain low contact resistance during repeated low-level operation. This reflects a different optimisation focus to snap-action designs intended for higher load switching.

Contact design and operator interaction

One of the most practical differences between snap-action and shorting bar designs is how the operator experiences the switch.

Snap-action models provide a clear tactile signal when the contact changes state. This can support consistent interaction or confirmation of actuation in operation.

Shorting bar models rely on visual or system-level feedback rather than tactile confirmation. Operator movement and contact transition remain mechanically linked, without a defined snap point.

These behaviours are inherent to the contact design and are typically addressed early in specification.

Electrical performance and life ratings

The P9 Series data highlights the relationship between contact design, load conditions, and life expectancy.

Mechanical life for the P9 Dome series is specified as a minimum of one million cycles. Electrical life varies depending on load and contact configuration.

At full rated load of 5 amperes resistive or 3 amperes inductive, electrical life is specified at a minimum of 25,000 operations. Under low-level switching conditions, electrical life extends to up to one million operations.

These values illustrate the relationship between contact design and load conditions. Mechanical endurance does not override electrical limits, and electrical ratings should not be extrapolated beyond the published values.

Integration considerations

The P9 Series is offered with threaded mounting for hex nut installation or with snap-in case options, depending on configuration. Termination styles include solder, PC pin, and 0.110 inch quick connect options.

Sealing options range from dusttight and moistureproof constructions to watertight sealing rated to IP68 when the appropriate suffix is specified. The sealing option selected does not change the internal contact design, but it does influence suitability for environmental exposure.

Operating temperature is specified from minus 55 degrees Celsius to plus 85 degrees Celsius.

These characteristics form the context in which the contact design operates and should be verified alongside electrical and mechanical requirements.

Choosing between snap-action and shorting bar designs

The distinction between snap-action and shorting bar pushbuttons reflects different electrical and mechanical behaviours.

Snap-action designs introduce a defined contact transfer point and tactile feedback, with ratings suitable for higher load switching within the published limits.

Shorting bar designs prioritise stable low-level switching with high contact pressure and extended electrical life under low current conditions, without tactile feedback.

The OTTO P9 Series makes this distinction explicit by offering both contact designs within the same family. This allows designers to select the configuration that aligns with the control requirement rather than adapting the requirement to the device.

The OTTO P9 Dome series includes both snap-action and shorting bar momentary pushbutton variants, with contact design, sealing, and force options varying by part number.