Drop the friction fit. Pull a PVC jacket once through a snug hole and it stretches, thins a fraction of a millimetre, and the contact that made the seal is gone. In about 5 mm [0.20 in] of height you still have two seals that hold. Use a rubber grommet under a cover plate, bored to about 90% of the jacket outside diameter and clamped to 20% compression. Or cast a thixotropic epoxy pot around the cable. Keep a true cable gland for the layout that can spare 15-20 mm [0.6-0.8 in] above the wall; it is the strongest seal and the only reusable one. Pick the grommet when the housing may be opened again; pick the pot when it may not.
Why the friction fit lets go
A snug hole gives you contact pressure and nothing else. Tension the cable and the jacket stretches lengthwise; plastics and rubbers barely change volume, so the stretched section goes thinner right where it passes through the hole. On a 6.0 mm jacket, 1% of thinning is 0.06 mm. That turns a light interference into a micro-gap, and water follows the gap along the cable itself.
Time does the same work. PVC held under compression creeps, so the closing force you designed in on day one relaxes over months outdoors. A friction fit is still the right choice for one job: keeping dust and drips off indoor electronics where you claim no rating. Give it a hole about 0.2-0.3 mm smaller than the jacket OD and expect it to loosen every time the cable is handled. Do not put a friction-fit entry on a housing you specify as watertight.
The four entries side by side
Four ways put a non-removable cable through a thin wall. The table sets their space needs against what each one actually holds.
| Seal | Height it needs | How it holds | Cable comes out? | Choose it for |
|---|---|---|---|---|
| Friction fit (jacket in a snug hole) | 0 mm extra | Contact pressure on the PVC alone | No, and pulling breaks it | Indoor dust and drips; nothing rated |
| Retained grommet | 5.0 mm total stack, plate included | Rubber at 15-25% compression, bore at 90% of jacket OD | No | Rain, splash and washdown in a tight opening |
| Thixotropic epoxy pot | Only the collar you cast | Epoxy bonded to the jacket | No | Immersion in a permanent install |
| M12 cable gland | 15-20 mm above the wall | A metal clamp compressing the jacket | Yes, reusable | Rated IP68 entries when the space exists |
Ratings in this table are manufacturer ratings; our enclosures are not UL listed. Whichever entry you pick, the housing is only as tight as its lowest-rated penetration: one loosened plug or one worn pushbutton gasket sets the rating for the whole box.
Where the retained grommet wins
The grommet owns the 5 mm case because plate, rubber and wall all live inside the height you have. Set it with three numbers. Bore the rubber to about 90% of the jacket OD, the common practice for rubber gripping cable: a 6.0 mm jacket takes a 5.4 mm bore and 10% of radial squeeze. Clamp the grommet's height by 15-25%, the squeeze band static seal practice uses for rubber face seals. Hold that clamp with bolts, because rubber under compression takes a set over the years and the closing force decays — the sandwich-seal failure worked through in rubber compression creep in clamped seals.
For a round boss rather than a slot, a flat cap over a standard 2.62 mm O-ring cord does the same job: 20% squeeze closes about 0.5 mm and keeps contact while the jacket moves. The groove arithmetic is the one in O-ring squeeze for a sealed enclosure face.
Match the rubber to the wash. EPDM runs about -50 to 150 C and is the pick for hot water, steam and caustics. Silicone spans about -60 to 200 C when heat is the enemy. Nitrile handles oil at about -30 to 120 C but dislikes hot water. These are elastomer handbook ranges; a named gasket's datasheet beats them for its own part.
Where the epoxy pot wins
Potting is the only method whose space need is the seal itself, so it fits where a grommet stack will not. It is also standard practice on submersible equipment: cable penetrators are sealed by casting a thixotropic, non-sag epoxy collar around the jacket, which is how a submersible's tether survives water pressure.
The work is small. Clean the jacket with isopropyl alcohol and scuff it lightly so the epoxy keys in. Form a tape dam, pour, and cure to the compound datasheet; a room-temperature cure stays far below the roughly 70 C continuous rating that cable standards give a PVC jacket. Anchor the cable within about 50 mm of the collar so flex loads the clamp instead of the bond line. Route the cable before you pour, because a pot is permanent.
The trade is service: the cable cannot come out and the seal cannot be inspected without cutting it away. For an entry that must never leak, in a few millimetres of space, that is a trade worth making.
Where the cable gland wins
When the wall can carry the height, a gland beats both grommet and pot. Its metal clamp grips the jacket, the seal rides along with cable movement, and the cable stays replaceable. An M12 gland passes through a 12.3 mm clearance hole (typical for the size; the gland's own drawing is final) and stands about 15-20 mm [0.6-0.8 in] above the wall for body and dome nut. That is exactly why it fails the 5 mm case.
If glands are new to you, start with what a cable gland does for an enclosure. Match the gland clamping range to the cable: small PG7-style glands clamp about 3-6.5 mm jackets, and their fit is checked in the PG7 gland alternatives notes. Cut the hole the same way as M20 gland hole sizes in plastic and aluminum, then fit it so the rating survives with install a cable gland without losing the rating. Flat jackets change the clamp, so follow the flat-cable gland approach. The cutouts, glands and windows guide carries the fundamentals, including the standard knockout diameters listed in UL 50 Table 71-1A.
A gland marked IP68 holds the code as its manufacturer states it. In IEC 60529 the second digit 8 means continuous immersion under conditions the maker and user agree on. Any lower-rated fitting elsewhere in the housing sets the assembly rating.
A 6 mm jacket sealed in 5 mm of height
The inputs:
- Height available: 5.0 mm [0.20 in] — the tight opening this article answers.
- Jacket outside diameter: 6.0 mm [0.24 in] — an assumption for the arithmetic; measure the real jacket before you order.
- Cover plate: 1.5 mm stainless sheet, typical.
- Targets: bore at 90% of jacket OD; height compression in the 15-25% static-seal band.
The rule: the compressed stack must equal the opening, the bore takes 0.9 times the jacket OD, and the free rubber height equals the compressed height divided by one minus the compression.
The arithmetic:
- Bore: 0.9 × 6.0 mm = 5.4 mm. Interference on the jacket: 6.0 − 5.4 = 0.6 mm, which is 10% of the OD.
- Stack: 1.5 mm plate + 3.5 mm compressed rubber = 5.0 mm, exactly the opening.
- Free rubber height: 3.5 / 0.8 = 4.4 mm. Squeeze: (4.4 − 3.5) / 4.4 = 20%, inside the 15-25% band.
- Wall fit: a 7.0 mm hole takes a 7.5 mm grommet body with 0.25 mm of radial interference per side, and the 20% vertical squeeze bulges the rubber outward onto the wall.
- Pull check: a hard pull that thins the jacket 2% takes 6.00 mm down to 5.88 mm. Against the 5.4 mm bore, 0.48 mm of interference remains, so contact survives.
Result: the seal fits the 5 mm opening and stays under compression both at rest and under pull. The number that moves the decision is height: keep the grommet up to about 15 mm of space, take the M12 gland from 15-20 mm upward, and go to potting below 5 mm.
The decision, and what to order
| Environment | Seal to use | The number that decides it |
|---|---|---|
| Indoor dust and drips | Friction fit | Hole 0.2-0.3 mm under the jacket OD; claim no rating |
| Rain, splash, washdown | Retained grommet | Bore 90% of OD, 20% height squeeze, stack inside 5.0 mm |
| Immersion, permanent install | Thixotropic epoxy pot | Collar cast to the space; cure below the jacket's 70 C rating |
| Rated and serviceable | M12 gland | 12.3 mm hole, 15-20 mm of height, clamp matched to the jacket |
When the housing is one of our stainless bodies, place the entry with the cutout designer; it lays out holes, glands and operators on any face, checks spacing and exports the layout with the quote request. Where the entry needs a cast pocket or a thicker local wall rather than a plain hole, start from custom stainless enclosures with new openings and settle the seal on the approval drawing before we cut.
Either way the order is three lines: hole size and position, the seal (a grommet drawing, a potting compound or a gland model), and the clamp or anchor that keeps it loaded. The box is delivered in 10 business days, counted from your approval of the drawing for custom work.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| 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 friction fit between a PVC jacket and the hole stay waterproof?
Only where you claim no rating: a snug hole keeps dust and drips off indoor electronics. At the first firm pull the jacket stretches and thins a fraction of a millimetre, contact breaks, and water follows the cable. Anything rated needs a captured seal: a grommet held at 20% compression or an epoxy pot.
How much compression should the grommet hold on the cable?
Bore the rubber to about 90% of the jacket OD: a 6.0 mm jacket takes a 5.4 mm bore, 0.6 mm of interference and about 10% radial squeeze. Clamp the grommet's height by 15-25%, and keep that clamp permanent with bolts so compression set cannot unload the seal.
Will epoxy potting work when the space is even tighter than 5 mm?
Yes. The seal is the epoxy collar itself, so it takes only the thickness you cast; submersible equipment seals its cable penetrators with thixotropic, non-sag epoxy for exactly this reason. Clean and scuff the jacket, anchor the cable so bending does not load the bond, and cure to the compound datasheet. Plan the cable route first: the pot is permanent.
How much room does an M12 cable gland need?
About 15-20 mm of height above the wall for its body and dome nut, plus a 12.3 mm clearance hole — typical M12 geometry; the gland's drawing gives its exact stand-off. That is why a gland rarely fits a 5 mm entry. Where the space exists, it is the best option: metal clamp on the jacket, manufacturer-rated IP68, and the cable stays replaceable.
Which rubber suits the grommet in a washdown box?
EPDM for hot water and steam: about -50 to 150 C, and the best against caustics. Pick silicone where heat alone rules the choice, and nitrile where oil does; the body of this article carries their full ranges. A named gasket's datasheet beats every handbook range for its own part.
