Cable gland selection rule
Cable gland selection requires two independent matches: the cable outside diameter must fit the gland sealing range, and the gland entry thread must fit the enclosure opening.
Threadgland = ThreadentryM, PG, NPT, and G/BSPP designations are different thread systems and must not be treated as interchangeable.
where:
- ODcable
- Measured outside diameter over the cable sheath[mm]
- ODmin
- Minimum sealing diameter from the gland datasheet[mm]
- ODmax
- Maximum sealing diameter from the gland datasheet[mm]
- Threadgland
- Cable gland male entry thread
- Threadentry
- Enclosure threaded entry or matching locknut system
Thread size is not the same as sealing range. Final gland selection must verify material, IP rating, thread length, armor termination, and hazardous-area certification where applicable.
How to choose cable gland size
Cable gland selection starts with the measured outside diameter of the finished cable, not conductor cross-section. The cable diameter must fall inside the manufacturer's sealing range, while the entry thread must match the enclosure opening or approved adaptor.
- Measure cable outside diameter over the outer sheath.
- Identify armored or unarmored cable construction.
- Choose indoor, outdoor, or hazardous-area service.
- Match cable OD to the gland sealing range.
- Verify thread, material, IP or environmental rating, armor termination, and certification.
Cable gland selection modes
Use Cable OD mode when the finished cable is available to measure. Use Metric M, PG, NPT, or G/BSPP mode when the enclosure entry thread is already known. Thread mode reports standard geometry and a common product-range reference, but the selected VIOX product datasheet remains the source of truth for clamping range.
| Mode | Standard or designation | Important characteristic |
|---|---|---|
| Cable OD | Manufacturer product data | Matches the sealing insert to measured cable OD |
| Metric M | ISO metric thread | Parallel; size number is nominal major diameter in mm |
| PG | DIN 40430 | Parallel legacy electrical conduit thread |
| NPT | ASME B1.20.1 | Tapered pipe thread; nominal size is not measured OD |
| G / BSPP | ISO 228-1 | Parallel pipe thread; normally seals outside the thread |
M, PG, NPT, and G cable gland thread chart
The same cable diameter may be available in more than one entry thread because the sealing insert and the enclosure connection are separate parts of gland design. Never choose an adaptor from nominal labels alone; compare the exact thread standard, major diameter, pitch, taper, sealing method, engagement length, and enclosure wall thickness.
| Thread family | Common sizes covered | Form | Selection note |
|---|---|---|---|
| Metric M | M12 to M90 | Parallel | Check pitch; 1.5 mm is common but not universal |
| PG | PG7 to PG48 | Parallel | Do not substitute a nearby metric diameter |
| NPT | 1/4 to 2 in | Tapered 1:16 | Use matching NPT entry and approved sealing practice |
| G / BSPP | G 1/4 to G 2 | Parallel | Usually requires a gasket or sealing face outside the thread |
Cable gland thread size vs. sealing range
Thread size describes the enclosure entry connection. Sealing range describes the cable diameters that the gland can clamp and seal. Different gland designs can use the same thread while offering different cable ranges, so thread size alone is not enough for selection.
| Dimension | What it must match |
|---|---|
| Cable sealing range | Measured cable outside diameter |
| Entry thread | Enclosure hole, threaded entry, or adaptor |
| Thread length | Wall thickness and locknut engagement |
| Armor range | Actual armor type and dimensions |
Armored vs. unarmored cable glands
Unarmored glands primarily provide sealing and strain relief. Armored cable glands must also terminate and, where required, bond the armor correctly. Cable construction such as steel wire armor, tape armor, braid, or screened cable changes the suitable gland design.
Information needed before ordering cable glands
Record cable OD, cable construction, armor dimensions, enclosure entry thread, required material, environmental exposure, temperature range, ingress protection, earthing or bonding need, and any hazardous-area classification. Final selection must use the gland manufacturer's certified range and installation instructions.
Assumptions
- Reference clamping ranges represent common nylon gland proportions, not a universal thread property
- Exact sealing range depends on product series
- Cable OD is measured over the outer sheath
Important Warnings
- Always verify the cable gland datasheet sealing range, thread, IP rating, material, and certification.
- Hazardous areas require properly certified glands and installation practices.