Short answer: a cable gland is the mechanical fitting that carries a cable through an enclosure wall and does three jobs in one part. It grips the cable, so pull and vibration stop at the gland instead of at your terminals. It seals the hole, on the cable sheath and on the plate, so the enclosure keeps its rating. On armoured or braided cable it also bonds that metal layer to the enclosure ground. You choose one by thread — M20 metric or 1/2 in NPT covers most panels — and by the seal's cable range. Choose wrong and the failure carries a signature: water inside, a conductor pulled off its terminal, or a ground path that reads open.
The three jobs, and how each one fails
Each job has its own failure signature, so read the symptom and you know which part of the gland to go after.
| Job | How the gland does it | What you see when it fails |
|---|---|---|
| Strain relief | The clamping seal and grip rings bite the outer sheath; pull stops at the body | Conductor loose in its terminal, intermittent signal, cable twisted out of the machine |
| Seal | An elastomer ring closes on the sheath; a second seal closes the flange to the plate | Water or dust inside, corroded terminals, a fogged window |
| Armour bond | An inner cone grips wire armour or braid against the metal body; the locknut lands the body on the plate | Ground path open or noisy on armoured cable; earth-fault trips |
Water on the floor of the box is a seal that never closed on the sheath, or never sealed against the plate. A conductor that has walked out of its terminal is strain relief that never gripped: the cable moved, and the terminal paid for it. A ground reading that comes and goes as you flex the cable is the armour clamp, and no amount of torque on the nut fixes that one — the armour has to land under the cone.
Threads, plates and holes
The gland threads into a drilled hole in the wall or into a gland plate, seals to that face under its flange, and takes a locknut on the inside. Metric bodies run M12, M16, M20, M25 and M32; an M32 body carries a 32 mm [1.26 in] thread about 9 mm [0.35 in] long, so it clears a 3 mm plate with length left for the nut. North American panels more often use 1/2, 3/4 and 1 in NPT bodies, sold as cable connectors or fittings. The usual clearance hole is the thread plus 0.5 mm: 20.5 mm [0.81 in] for M20, 25.5 mm for M25. Panels built to US knockouts take the hole size from UL 50's Table 71-1A, which prints the knockout diameter matching each trade-size fitting, so the number comes from the table rather than a drill-bit guess.
For the hole itself, drilling the M20 hole in plastic and aluminum covers drill sizes and technique; where the panel is thick, or you only need chafing protection, see grommet vs gland in a thick panel. Every hole you add is a hole through a rating, and what drilling does to an enclosure's rating explains when a field cut costs you the type. Our stainless bodies arrive with the gland holes cut and deburred at the factory: the cutout designer lays them out on any face of a catalog size, and custom stainless enclosures carry the same holes on a made-to-order body. The cutouts, glands and HMI windows guide collects the related hole sizes for operators and displays.
What the ratings test, and what they leave out
A gland earns an IP code with a cable installed, so the rating describes the gland-and-cable pair rather than the fitting alone. IEC 60529 tests the second digit 6 with a 12.5 mm nozzle delivering 100 L/min from 2.5 to 3 m [8.2 to 9.8 ft] for at least 3 min; digit 7 means 1 m [3.3 ft] of still water for 30 min; digit 8 is continuous immersion at a depth and time the manufacturer declares. The gland's own product standard, IEC 62444, sets tests for clamping, for sealing and, where the gland has one, for the armour termination — the three jobs again, proved one at a time.
What the ratings leave out is your cable. The number was earned with a cable inside the seal's range, and outside that range there is no tested seal: a 9 mm cable will not even pass a seal whose maximum sits below that. Match the seal range to the cable shows how to read the range off the datasheet and the cable. Water can also travel down the inside of a cable and arrive past a gland that is sealing perfectly; stopping water wicking through a cable deals with that one. For the difference between keeping water out and keeping gas out, see what watertight and gas-tight gland ratings prove.
On the enclosure side of the joint, our boxes are rated NEMA 4X / IP66 by the manufacturer and not UL listed. NEMA 250 also makes 4X a corrosion rating: its Table 5-1D calls for 200 h of salt spray judged against a type 304 stainless specimen. A bare-steel fitting in a stainless wall is the weak link that test would find first, which is why the gland material matters as much as the box material.
Plastic, brass or stainless
Most metal glands come as nickel-plated brass or stainless steel, and plastic bodies — usually polyamide — fill the benches where no armour ever shows up. Match the body to the cable and the room:
| Body | Pick it for | The limit |
|---|---|---|
| Plastic (polyamide) | Plain unarmoured control and data cable, dry rooms or light splash | No armour or braid bond |
| Nickel-plated brass | Power, instrumentation and shielded cable, general industrial rooms | Plating can pit under daily hot caustic washdown |
| 316 stainless | Washdown, food and coastal rooms; pairs galvanically with a 316L body | — |
The rule underneath the table: if the cable has armour, braid or a metallic sheath, the gland must be metal with a clamp for that layer, because plastic has nothing to bond it to.
The third job: bonding armour and braid
On steel-wire-armoured or braided cable the gland is the ground path. The armour lands under the cone, the cone is part of the body, the body pulls down on the plate, and the plate carries fault current to the enclosure ground stud. NEC 250.96(A) states the principle: metal parts that serve as the grounding path — raceways, cable armour, enclosures — must be bonded together so they carry any fault current imposed on them. Where the enclosure is painted, NEC 250.12 wants paint, lacquer and enamel off the threads and contact surfaces before the locknut and washer land. Stainless bodies ship bare, which takes that job off your list.
Check the bond with the circuit dead: lock out the feeder, confirm the absence of voltage, then read ohms from the armour to the ground stud. A healthy clamp reads well under 1 Ω; a reading that changes as you flex the cable says the cone never bit. For where the grounding conductor itself should enter and land, see grounding conductor entry: connector and bond alongside the enclosure grounding and bonding guide. For the same three jobs worked on one real cable, sizing an M20 gland for a 1.5 mm² armoured cable is a good walkthrough.
A worked entry set
Take a 12 × 10 × 6 in [305 × 254 × 152 mm] 316L stainless box on a food-line wall, with everything entering the bottom face so nothing looks up at the hose. The cables: five unarmoured control cables at 6.5 mm [0.26 in] OD, and one braided shield cable at 11.0 mm [0.43 in] OD.
Pick each gland from the cable, aimed mid-range where the seal wants to work. An M20 with a seal listed 4–8 mm takes each control cable: 6.5 mm sits 2.5 mm off the minimum and 1.5 mm off the maximum. The braided cable takes an M25 with a braid clamp and a seal listed 9–14 mm: 11.0 mm leaves 2.0 mm and 3.0 mm of margin.
Now the holes. Lay the five M20 holes on 35 mm centres — locknuts on these sizes run about 27 mm across, and that spacing clears them with steel to spare — and give the bigger M25 hole 45 mm of clearance. The row spans 4 × 35 + 45 = 185 mm centre to centre, so a 305 mm body leaves 305 − 185 = 120 mm, or 60 mm at each end for the mounting ears and a ground stud. One drawing, six holes, no field drilling.
What to specify
Put this on the order or the approval drawing:
- Thread standard and size for every entry — M20 and M25 here, or 1/2 and 3/4 in NPT — with one gland per cable.
- The measured cable OD against each seal range, aimed at mid-range, written beside each hole on the layout.
- Body material by room: plastic for unarmoured cable in benign rooms, nickel-plated brass for general duty, 316 stainless for washdown on a 316L body.
- A braid or armour clamp on every cable that has one, and a rated blanking plug in every spare hole, because an open hole leaks exactly like a failed seal.
- Factory-cut entries laid out in the cutout designer or sent as a drawing for a custom stainless enclosure; both are delivered in 10 business days, counted from your order, and custom work from your approval of the drawing.
One boundary worth knowing: a classified area needs a gland certified for that area and an enclosure built for it. We do not build hazardous-location enclosures, so that order belongs with a supplier who does.
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
What is the difference between a cable gland and a conduit fitting?
A gland grips and seals the cable itself; a conduit hub seals a threaded pipe, and the wires run inside that pipe to their own box. Both come in the same trade territory — 1/2 and 3/4 in NPT in North America, M20 and M25 metric elsewhere — so the holes look similar, but the part doing the sealing differs. Use a gland where the cable ends at the enclosure, and a hub where conduit carries the wires onward.
Can a plastic cable gland reach IP68?
Yes. The rating comes from the elastomer seal closing on a cable inside its listed range, and a plastic body earns IP68 the same way a metal one does. Plastic, usually polyamide, typically spans −40 to +100 C [−40 to 212 F]. What plastic cannot do is bond armour or braid, so keep it on plain unarmoured cable.
Why does a gland leak even when the nut is tight?
Three usual causes. The cable OD sits below the seal's minimum, so the ring never closes — a 3.5 mm cable in a seal that starts at 4 mm leaks at any torque. The seal washer between flange and plate is missing or crossed. Or the water is travelling down the inside of the cable itself, arriving past a gland that is doing its job.
Can I fit a 1/2 in NPT gland into an M20 hole?
No. A 1/2 in NPT gland wants a 7/8 in [22.2 mm] hole with a tapered thread — 1.7 mm larger than an M20 needs — while the M20 body is a straight 20 mm thread. The different diameters and thread forms mean neither part engages or seals in the other's hole, so pick one thread system and order every locknut, plug and spare to match it.
Can two cables share one cable gland?
As a rule, one cable per gland. Two cables can share only a gland whose seal is listed for multiple entries, with both ODs inside the stated range — for example two 4.5 mm control cables in a dual seal marked for that use. Armoured or braided cable never shares, because the clamp has to close on one clean armour bed.
