Calipers across an old panel hole tell you more than any catalogue page, and they usually tell you something inconvenient. We ask for that one measurement before anything else in a replacement inquiry, and the answers come back spread across a surprising range: 22.3, 22.5, 25.4, once 23 and a bit where somebody had filed the edge. Every one of those panels was called “22 mm” by its owner, and only some of them were right.
This piece is about modular 22 mm industrial push buttons, selector switches, key switches and emergency stops of the IEC 60947-5-1 kind on machine control panels and enclosures. It assumes the panel is yours to modify if modification comes to that, and it does not override whatever your machine’s safety assessment demands of an emergency stop device. ACXION supplies the XH2 and LA135 ranges referred to throughout.
The size in the name is not the size of the hole
The most common reason a replacement will not fit is that “22 mm” names a family, not a measurement. Our XH2 range and the 22 mm families inside the LA135 range both call for a panel cut out of 22.3 mm. The compact 16 mm LA135 families call for 16.2 mm. Cut out drawings for both catalogue sets live on the downloads page, and they are worth having open before you measure rather than after.
So if the calipers read 22.3 or a shade over, nothing has gone wrong with the panel. That is a 22 mm device doing what the standard expects. Read 25.4 and you have found an inch size legacy part, which changes the conversation entirely, because the options then are adapters, redrilling, or a plate. Read something between the two and the panel has probably been modified by hand at some point in its life. Measure it twice, and photograph it.
The notch that nobody remembers ordering
The second trap is harder to see. Many 22 mm heads carry a locating boss underneath that drops into a small notch at the edge of the panel hole. Its job is to stop the head turning under a gloved hand, or after ten years of machine vibration.
Order a bossed variant for a hole with no notch and the new part will not sit flat. We see this often enough that the XH2 range is offered with both plain and bossed housings, and the choice belongs on the order, not in the toolbox. Filing the boss off damages the plating and can lift the sealing ring. Cutting a notch into an installed panel drops swarf into whatever lives behind the door. The reverse combination also misbehaves: a plain body will enter a notched hole, but the head will rotate, and once it rotates the legend stops matching the rest of the row. Both housing variants, along with the replacement contact blocks that go behind them, sit under push button switches.
What the neighbours on the panel will tolerate
Even a device that fits its own hole has to coexist with the devices beside it. The XH2 catalogue sets minimum mounting dimensions, and they are not uniform across operator types. Push button, selector and key switch all need 30 mm centre to centre and 50 mm row to row. A mushroom head needs 40 mm centre to centre. An emergency stop needs 50 mm in both directions.
That last line catches people halfway through an upgrade. Converting a plain start button into a mushroom head e stop raises the clearance it demands, and a neighbour sitting 30 mm away that was fine yesterday is not fine tomorrow. It is easier to move a legend plate in advance than to discover this while holding the new switch. On doors where two units share a narrow strip, row to row is usually the first figure to fail, so measure it twice.
Going smaller has its own price. The 16 mm LA135 bodies are rated Ui 250 V, Ith 5 A. The 22 mm bodies: 400 V, 10 A. Not the same device in a smaller box. A swap made to save width quietly reduces what the device is allowed to switch, which matters if the load is inductive.
The depth behind the door
Almost nobody measures behind the panel. A standard three piece button consists of head, mounting frame and contact block, and most doors have room to spare. Add illumination and a fourth piece appears, because the LED block sits between frame and contact. A second block for feedback and it grows again.
You find out at the end, when the door will not close, or closes onto a wire it should not touch. Our standing advice is to photograph the back of the panel with the old device still fitted, then compare the available depth against the stack height the new part needs. The photograph also settles the question of which ring nut went where, which nobody remembers.
Matching what the operators already know
One button died and the rest of the row has years left. Keeping the replacement identical matters for reasons that have nothing to do with switching. People find controls by position and colour, not by part number. A replacement that works identically but looks slightly off will be found more slowly by everyone on that door, for months.
Original still in production? Order the same model. Read the code off the old part before it goes in the bin. After the bin, the code is gone. Where the original is unknown, the measurable things are the cut out, the head style, the contact arrangement, hold or spring return, and lit or unlit. On the holding question, our 1NO1NC latching raised head push button shares its footprint with the momentary version, so the swap is invisible from the front of the door.
The swap itself, in order
- Photograph the legend and the wiring first. Nothing comes off before that.
- Block off the back first. Then the collar. Then the actuator comes out forward.
- Fit the sealing ring to the new actuator before it enters the hole.
- Line up the triangular marks on head and frame, then push the frame home.
- Tighten to 1.0 to 1.2 N·m on the XH2 assembly, which is far less than finger strength suggests, and over torque distorts the seal.
- Wire the contact block, two conductors of 0.5 to 2.5 mm² per terminal, and avoid pairing unequal sizes under one screw.
Two rules survive from every teardown we have done on failed assemblies. Do not press on the marked side of a contact module when removing it. And keep the screwdriver angle below ten degrees. Retaining tabs break easily, and a broken tab turns a block swap into a head swap.
If a case is easier to hand over than to measure, send the cut out reading, a photo of the front, a photo of the back, the panel thickness and the load to switch. Four items in one message through the contact page usually picks the part in a single pass, collar thread length included.
The hole was cut by somebody you never met, and it will still be there at the next rebuild. Twenty two point three millimetres, a notch at the edge, and enough depth behind the door: written down in that order, a stranger’s cut out stops being a gamble and becomes an ordinary specification.