Measure the actual outer diameter
Datasheet values are nominal with a tolerance often of ±0.4 mm; PUR sheaths also expand with temperature. Measure with callipers at three points and use the largest value. On screened cables measure over the sheath, not the braid.
Choosing grommet size within the clamping range
Every grommet has a clamping range, e.g. 6–10 mm. At the upper limit the membrane tears during fitting; at the lower limit it does not clamp and leaks. Aim for mid-range. For cables with a large connector housing choose an open-sided or split grommet.
Occupancy rules and reserve
Large grommets occupy two or three positions; check the maker's occupancy table. Plan 20% spare positions as standard — machines always grow — and keep power and signal cables in separate frame halves to limit coupling.
Check cut-out and build depth
Besides frame size, the free space behind the wall matters: cables must turn away within their bend radius. Allow at least 4 × cable diameter of free depth, more for stiff power cables. Also check the bolts remain reachable after rails and terminals are fitted.
| Cable Ø (mm) | Grommet range | Positions | Note |
|---|---|---|---|
| 2–4 | 1,5–4,5 | 1 | Signaal, sensor |
| 5–8 | 4–9 | 1 | Ethernet, bus |
| 9–13 | 8–14 | 1 | Servo klein |
| 14–20 | 13–21 | 2 | Vermogen |
| 21–30 | 20–32 | 3 | Hoofdtoevoer |
Frequently asked questions
- May I run two thin cables through one grommet?
- Only with a grommet approved for it (multi-grommet). Two cables in a single membrane always leave a leak gap in the middle.
- What if my cable sits exactly between two grommet sizes?
- Choose the smaller size: membranes stretch better than they clamp on an oversized opening. Do check the sheath is not constricted.
- Can you produce an occupancy layout?
- Yes. Send the cable list with diameters and whether connectors are fitted; you receive a frame proposal with grommet list, plugs and cut-out drawing.
Read next
- Cable entry systems: frames, grommets and brush sealsThe three main entry types, what they do and do not seal, and when you need a split frame.
- Which cable entry do you choose for pre-terminated cables?Split grommet, frame or snap entry: packing density, IP rating and strain relief compared.
- Installing an entry frame: sequence, sealing and checksFrom cut-out to final check: the eight steps that decide whether your frame really seals.