The 22 mm panel cut-out standard, contact configurations, momentary vs maintained operation, IP ratings on the front face, and how to specify an emergency stop correctly.
22 mm is the de facto standard for panel-mount operator devices, which makes mixing brands easy — and makes it easy to buy a device that fits the hole but not the circuit.
| Item | Typical 22 mm value | Check because |
|---|---|---|
| Mounting hole | 22.3 mm | 16 mm, 25 mm and 30 mm families exist and are not interchangeable |
| Panel thickness | 1–6 mm | Thicker plates need a longer threaded collar or a different fixing |
| Behind-panel depth | 40–60 mm with contact blocks | Deep devices foul DIN rail or terminal blocks behind the plate |
| Front bezel | 28–30 mm | Determines the minimum spacing between adjacent devices |
Always check the depth with the contact blocks fitted, not the bare actuator. The single most common panel-building rework is a row of devices that will not clear the terminals behind them.
Devices are supplied as a holder plus contact blocks. You need to state how many normally-open (NO) and normally-closed (NC) contacts each position requires, and whether the elements are late-break/early-make (mechanically interlocked so NO and NC cannot close together) for changeover duty. Ordering "one pushbutton" without that information guarantees a second shipment.
Momentary returns to rest when released: start buttons, jog, test, reset signals. Maintained (latching, or a selector switch) stays where it is put: on/off, auto/manual, mode selection. A two-position selector is usually stay-put/return-on-key-removed depending on the type; a three-position selector gives left/centre/right with the centre usually maintained.
Illuminated actuators take an integral lamp or LED module in a specified voltage — commonly 24 V AC/DC, 110 V and 230 V. Specify the voltage and whether the lamp is fed from the control rail or the field circuit. Where the same function must be visible in a bright and a dark area, a two-colour or a separate pilot light is clearer than an illuminated button alone.
An emergency stop is not just a red mushroom button. It must be a latching, mechanically held device that stays operated until deliberately reset, and it must be wired as a normally-closed contact so a broken wire also stops the machine. The reset must not restart the machine — it only clears the stop state, and starting is a separate deliberate action.
Practical specification points: 40 mm or larger mushroom head, red actuator on a yellow background, latching push-lock or twist-release per your standard, direct opening action on the NC contact, and IP rating to suit the environment. Where the machine has several operating positions, provide one at each. Whether a guard interlock or a monitored relay is required is governed by your risk assessment and the applicable machinery safety standard, not by the button itself — confirm the safety circuit with the person responsible for the risk assessment.
The IP figure on a panel device almost always refers to the front face only. IP65 front / IP20 rear is normal: the front survives a wash-down, the terminals behind the plate do not. If the whole enclosure is washed down, the enclosure rating is what protects the terminals.
Common practice: green or black for start/on, red for stop/off and for emergency stop, yellow for emergency-stop background, white or amber for illuminated indication, blue for reset or mandatory action. Legend plates and engraved marking reduce operator error more than any other change you can make for the money.
ELEHPD supplies 22 mm pushbuttons, selector and key switches, pilot lights, emergency-stop devices and control stations (metal and insulating), with contact blocks, legend plates and enclosures quoted together.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.