In brief
A cable gland brings a cable into an enclosure with a seal and strain relief, protecting the entry against dust, water and the cable being pulled out.
Contents
What is Cable gland?
Cable glands are fitted wherever cables enter control cabinets, terminal boxes, motors or devices. When the dome cap nut is tightened, a sealing insert is pressed radially against the cable sheath. This creates the seal and at the same time a strain relief that protects the terminal points inside from mechanical stress.
Key parameters are connection thread, clamping range, material, IP rating and temperature range. Today, metric threads such as M16x1.5, M20x1.5 or M25x1.5 dominate; older plants still have PG threads (steel conduit thread). Materials are polyamide, nickel-plated brass and stainless steel, for example for food or chemical areas. Special versions are available for EMC with shield contact, for potentially explosive atmospheres, with bend protection or as multiple-hole inserts for several cables.
Failures are caused by embrittled sealing inserts, an incorrectly selected clamping range, missing locknuts or sealing rings, and UV or chemical exposure. A leaking entry can let moisture into terminal boxes and electronics. As a typical C-part, the cable gland is often underestimated in purchasing. A small, standardised selection of common thread sizes and clamping ranges in stock prevents a missing small part from delaying a repair in the control cabinet.
In practice: maintenance and procurement
For a replacement, the thread size and type, thread length, clamping range matching the cable outer diameter, material, degree of protection and, where applicable, EMC or Ex version are needed. The locknut and sealing ring should be ordered at the same time.
Synonyms and abbreviations: cable entry · metric cable gland · PG cable gland · EMC cable gland · cable connector gland
Frequently asked questions
What is the difference between PG and metric cable glands?
PG stands for an older thread system originally developed for steel conduit, with its own flank angle and pitches. Metric cable glands use ISO fine threads with a 1.5 mm pitch and have largely replaced PG in new installations. The two systems are not directly compatible. Reducers or adapters are available for existing enclosure holes with PG threads.
How is the right clamping range selected?
The clamping range states the minimum and maximum cable outer diameter for which the gland seals and provides strain relief. The actual diameter of the cable should be measured and should lie as close as possible to the middle of this range. If it is at the edge, sealing or strain relief suffers.
What information is needed to order a cable gland?
Important are thread size and thread type, thread length to suit the wall thickness, clamping range, material, degree of protection and temperature range. Special requirements such as EMC shielding, suitability for potentially explosive atmospheres or food-grade design are added. Locknuts and sealing rings are often listed separately. A photo of the installation makes identification easier.
When is an EMC cable gland needed?
An EMC cable gland is used when the shield of a shielded cable is to be connected to the enclosure over a large area. This is typical for motor cables on frequency inverters, servo drives or sensitive measuring equipment. Contact around the full circumference dissipates interference currents better than a single shield connection wire.