Mount rarely-used operators on the backplate and leave the door skin whole. Operators here means pilot devices: pushbuttons, selector switches, key switches and pilot lights, the parts that normally puncture a door. Two internal options cover almost every case — a DIN-rail base that presents a 22 mm hole for each device, or a small sub-enclosure bolted to the backplate and pre-drilled for a bank of operators. Either way you add zero holes to the sealed envelope, so a box rated NEMA 4X / IP66 by the manufacturer (not UL listed) keeps its one continuous door gasket. Anything a machine operator touches every shift still belongs on the door; everything else can live inside.
Why mount operators inside the enclosure?
Because every hole you put in a door is a joint that can leak: six gasketed operators mean six extra seals, and the door is only as tight as the weakest of them. Mounting inside adds zero holes, so the rating rides on the one gasket the box was built with.
An assembled panel carries the rating of its weakest part. A gasketed operator rated IP66 holds a Type 4X door at that point; a bargain IP54 operator pulls the whole face down to IP54. What a panel keeps after you cut it and mount devices works through that arithmetic for every kind of add-on. An operator on the backplate sits behind the gasket, so its own ingress rating stops mattering: an unsealed device that would drown on a door works fine on a backplate.
Access control comes free with the move. Changing a mode now means opening the panel, and you open the panel under lockout, so settings move only when someone is already doing maintenance work. The door also stays clean for the HMI and the few controls that earn their holes — sealing door-mounted buttons and indicators covers that side of the decision.
What hole size does a 22 mm operator need?
A 22 mm operator mounts in a 22.5 mm [0.89 in] hole and the larger 30 mm device in a 30.5 mm [1.20 in] hole — diameters fixed by the IEC pilot-device standards, while NEMA standards set no hole size at all.
Those diameters come from IEC 60947-5-1, the pilot-device standard, and "NEMA" devices drill the same IEC holes, because NEMA enclosure standards simply leave hole size to the device maker. A matching step bit cuts each hole cleanly in a bracket or a sub-enclosure lid. Cut at nominal size: the locking collar grips the hole edge, and an oversized cut lets the device spin when you lean on it. For dense banks, the compact 16 mm range drills a smaller hole again and takes the same contact blocks.
How far apart do you space internal operators?
Set them 30 mm [1.18 in] apart side to side and 40 mm [1.57 in] top to bottom, center to center — those are the published minimums for 22 mm operators, and they double as a comfortable layout pitch.
Give yourself 40 mm across and 50 mm [1.97 in] vertically where the space exists, and a gloved hand works each device without knocking its neighbour. Legend plates sit under the collar and add to the face each device occupies, so the wider pitch absorbs them. On rail the spacing looks after itself: a DIN base is 40.8 mm [1.6 in] wide, so a row of bases lands on a 40.8 mm pitch with nothing to calculate. The backplate and DIN rail layout guide covers rail rows, duct runs and the clearances around both.
How much space does a bank of six selectors take?
About 60 x 110 mm [2.4 x 4.3 in] of lid for the holes in a two-column bank, or 245 mm [9.6 in] of rail if every selector rides its own base — a 150 x 110 mm [5.9 x 4.3 in] sub-enclosure swallows the whole bank with margin.
Take a bank of six: four axis selectors in manual/auto, one master key switch and one maintenance-enable switch. Two columns by three rows at the pitch above gives width = 1 gap x 30 mm + 1 hole x 22.5 mm = 52.5 mm, so plan 60 mm [2.4 in] with collars and legends. Height = 2 gaps x 40 mm + 1 hole x 22.5 mm = 102.5 mm, so plan 110 mm [4.3 in]. A 150 x 110 mm lid carries that with room for its own gasket.
The same six on DIN bases run along 6 x 40.8 mm = 245 mm [9.6 in] of 35 mm rail — 245 ÷ 17.5 = 14 standard modules. Either layout fits any backplate over 300 mm [11.8 in] wide, and the door still has zero holes in it.
Which internal mounting option fits your panel?
Pick the DIN-rail base for one to three scattered operators and a sub-enclosure for a bank of four or more, or for anything that must live under a lock — the base clips to 35 mm rail in minutes, and the sub-box brings its own lid.
| Option | What you get | Footprint | Best for |
|---|---|---|---|
| DIN-rail base, one per device | A 22 mm hole on 35 mm rail | 40.8 mm [1.6 in] of rail, about 51 x 41 mm [2.0 x 1.6 in], 58 mm [2.3 in] tall | 1–3 operators set next to the drive or PLC they configure |
| Sub-enclosure on the backplate | A lid drilled for the devices, latch or lock of its own | From about 150 x 110 mm [5.9 x 4.3 in] | Banks of 4–6 devices, settings under lock, grouped interface modules |
| Drilled bracket or plate | Any pattern of the standard hole sizes | Whatever you draw | 30 mm devices and one-off layouts |
The sub-enclosure earns its keep in three ways. You drill its lid on the bench, so no swarf lands on your rail; the lid keeps casual hands off the settings; and the box groups related hardware — the same trick that keeps intrinsic safety barriers and their switches together in one place. Bolt it to the backplate with fasteners that stay inside the envelope: self-tappers or rivet nuts into the plate. Treat any fastener that passes through the enclosure wall as a wall penetration and seal it the way you would seal a gland.
How do you mount the operators step by step?
Plan the bank, land it at the layout pitch, fix the bases or the sub-enclosure to the backplate, snap in the operators, wire them to the terminal strip, then close the door and prove nothing touches.
What you need:
- the operators, their contact blocks and legend plates
- one DIN-rail base per operator, or the sub-enclosure
- 35 mm DIN rail or a bracket, with self-tappers or rivet nuts
- step bits at both standard hole sizes
- labels, a lock-ring wrench, terminal strip and wire duct
- Split the device list by use. Anything pressed more than about once a week goes on the door; commissioning and maintenance settings stay inside.
- Place the bank where its wires land: next to the drive or PLC it configures, clear of duct runs, with 65 mm [2.6 in] of clear depth to the closed door.
- Fix the rail or the sub-enclosure. Mounting DIN rail on a backplate covers rail centers and cutting; sub-boxes bolt through the plate with fasteners that stay inside.
- Drill on the bench. Cut one hole, deburr it and test-fit an operator before you drill the rest of the pattern.
- Seat the operators: collar through the hole, legend plate under it, lock ring snug with the wrench.
- Wire and dress. Contact blocks snap on, wires run to the terminal strip, and duct stays at or below 50 % fill — the limit behind the NFPA 79-2012 duct-fill rule (section 13.5.2), since round cables leave air gaps.
- Prove it. Tug every operator, close the door slowly over the tallest device, label each position and photograph the as-left settings.
How much clearance do you leave to the closed door?
Allow 65 mm [2.6 in] from the backplate face to the closed door: a 22 mm operator on its DIN-rail base stands about 58 mm [2.3 in] tall, and an operator with one contact block reaches about 55 mm [2.2 in] behind its panel.
Two blocks under one selector push the stack past 70 mm [2.8 in], so count blocks before you fix the rail position. A door with an HMI window loses depth too, because the window mounts proud on the inside face. Measure the real gap instead of guessing it — the enclosure selector lists mounting-panel-to-door clearance by size. The old clay trick settles it: a blob of modelling clay on the tallest device, door closed, and the squash gives you the true clearance. Leave yourself reach as well: 80 mm [3.1 in] of free space in front of the bank lets a hand arrive past the duct without scraped knuckles.
What checks finish the job?
Three checks close it out: a firm tug on every operator and its lock ring, a slow door-close over the tallest device against your 65 mm [2.6 in] clearance, and a written as-left record of every selector position before the panel runs.
Do the door-close test de-energized: lock out and confirm absence of voltage before your hands go in, because an open door is the only thing between you and the terminals. Then finish the rest: legend plates legible from standing height, labels that say what each position does, and the as-left photo stored with the panel drawings. A bank nobody can read gets flipped to "whatever" within a month.
When does an operator still belong on the door?
Put it on the door when someone uses it more than about once a week: door mounting costs one hole and one gasketed operator, but it saves opening the panel every time a mode changes.
Decide by who touches the device and how often:
- Every shift or every run — door, with a gasketed operator rated IP66; that operator's rating is now the rating at that hole, so buy the sealed one.
- Commissioning and maintenance only — backplate, on bases or in a sub-enclosure.
- Maintenance authority only — inside a sub-enclosure with a lockable lid.
- Needed while the panel runs live — door, and read electrical enclosure door interlock basics before you decide who may open it.
When you order, the door can arrive uncut with the mounting panel ready for the bank: custom stainless enclosures build to your drawing, and the cutout designer lays out the few holes that do belong on the door — cutouts, glands and HMI windows covers how to specify each one. Custom work is delivered in 10 business days from your approval of the drawing.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 304 stainless | 16 x 14 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can a 30 mm operator go on a DIN-rail base?
No. The DIN-rail bases are built around the 22 mm operator's 22.5 mm hole, and none are offered for the larger size, so a 30 mm device drills into a bracket or a sub-enclosure lid. Inside a panel it costs you nothing: the faces of both device sizes are about the same, and the smaller one takes less rail.
Do holes in the backplate hurt the enclosure rating?
No. The rating lives in the enclosure skin, the door gasket and the seals at every wall penetration; the backplate and its brackets sit inside that envelope, so a hole there costs nothing. Any mounting bolt that passes through the enclosure wall is different: seal it the way you would seal a cable gland.
What contact block does an internal selector need for a PLC input?
Choose it by the load and the marking on the block. IEC 60947-5-1 stamps pilot contacts for AC-15 and DC-13 duty; a 24 V DC PLC input drawing a few milliamps wants gold-flashed contacts to stay clean, while a power circuit up to the block's typical 10 A marking takes standard silver contacts.
How do you stop production staff changing maintenance settings?
Put the bank behind a lid they cannot open: a sub-enclosure with a quarter-turn lock, or a lockable inner door on the backplate, with the key held by maintenance. A 150 x 110 mm sub-box lid carries a six-selector bank, and the main door lock still controls general access to the panel.
