Brass or plastic cable gland: What should I choose?

Introduction: Brass and Plastic Cable Gland

A cable gland, often called a stuffing box or sealed entry, serves to bring an electrical cable into the housing of equipment, a junction box, control cabinet or terminal box. It fixes the cable, protects the entry point from dust and moisture, and in some versions — from explosion. The two main types by housing material are brass and plastic. Both perform the same task, but the difference in material determines strength, resistance to the environment, temperature range, compatibility with metal conduit and the final price.

A brass cable gland is a metal product with nickel-plated or untreated coating, with metric threads M20, M25, M32 and other sizes. It withstands high mechanical loads, works in a wide temperature range and is mandatory in explosion-proof zones. A plastic cable gland is made of polyamide or nylon, often black, with the same metric threads. It is lighter, cheaper, not subject to corrosion, but inferior to brass in strength and heat resistance. More details about explosion-proof glands and proper selection can be read in the article about cable gland.

Comparative Table of Brass and Plastic Glands

Housing Material and Strength

A brass cable gland is made of brass, often with a nickel coating that protects against corrosion and gives an aesthetic appearance. The metal housing withstands strong mechanical impacts, constant vibration, alternating loads. Such a gland will not crack when tightened with high torque, will not deform in case of accidental tool impact. Therefore brass is chosen in heavy industry: on cranes, conveyors, ship equipment, railways.

A plastic cable gland is made of polyamide, which is distinguished by lightness, flexibility and good resistance to impacts at low temperatures. Polyamide does not rust, does not oxidise, but is inferior to brass in hardness and abrasion resistance. Tightening a plastic gland with excessive torque is not allowed: the thread may be stripped or the housing cracked. For most electrical enclosures, distribution boards and terminal boxes, the strength of polyamide is sufficient, especially if the cable is not subject to strong mechanical loads.

Sealing and IP Protection

Both types of glands provide a sealed cable entry when the sealing ring is correctly selected for the cable diameter. The IP68 protection degree is achieved both in brass and plastic models, if the manufacturer declares the corresponding class. The difference appears in severe conditions: brass holds compression better under temperature changes, does not lose sealing under vibration and dynamic loads. A plastic gland may weaken over time due to the creep of polyamide, especially at high temperatures. In a static environment and stable temperature, both types work equally reliably.

For damp rooms, outdoor installation, underground manholes, both brass and plastic glands with IP68 are suitable. However, under constant UV radiation, polyamide gradually degrades unless it contains stabilisers. Brass with nickel coating is not afraid of the sun, rain or salt fog. Therefore, on open marine platforms, in ports, on outdoor cabinets, brass is preferred.

Explosion-Proof Versions

An explosion-proof cable gland must comply with the requirements of GOST IEC 60079-0, GOST IEC 60079-1, GOST IEC 60079-7 and TR CU 012/2011. It must not only fix the cable, but also prevent the propagation of an explosion from the housing outwards, as well as withstand the explosion pressure inside. Brass glands in Ex d and Ex e versions are widely used in the oil and gas, chemical, and mining industries. The metal housing provides the necessary mechanical strength and thermal conductivity, which is important for explosion-proof enclosures.

Plastic cable glands with an Ex certificate also exist, but are used less often and mainly in zones with a low explosion hazard category, where non-metallic materials are permitted. Plastic does not have the same thermal conductivity and impact strength as brass, therefore it is not suitable for Ex d zones. If the facility is located in an explosion hazard zone of class 1 or 2 according to GOST 31610, the choice is almost always unambiguous — a brass explosion-proof gland.

Temperature Range and Chemical Resistance

A brass cable gland retains its working properties in the range from −60 to +200 °C, and individual models with silicone seals — up to +250 °C. This allows its use in cryogenic installations, hot workshops, near heating equipment. The metal does not melt when overheated, does not become brittle in frost. A plastic gland is limited by an upper limit of about +100 °C, and some polyamides lose strength already at +80 °C. For refrigeration chambers and moderate climates, polyamide is suitable, but for extreme temperatures — not.

As for chemical effects, brass is resistant to most oils, solvents, alkalis, but may corrode in an acidic environment. Nickel coating expands chemical inertness. Polyamide is resistant to oils, petrol, alcohols, but breaks down under the action of strong acids and some organic solvents. The choice of gland material is always checked against the specific environment where the equipment will be installed.

Installation, Threads and Compatibility with Metal Conduit

Both types of glands are installed in a housing with metric threads M20, M25, M32 and others. A wrench is sufficient for installation, and for a plastic gland, the tightening torque is indicated in the catalogue and is usually lower than for a brass one. Sealed cable entry is ensured by a sealing ring that compresses the cable sheath when the cap nut is tightened. For metal conduit, special glands with threads corresponding to the conduit diameter are used, while brass models combine better with metal conduit, creating a single metal shield and earthing.

A plastic gland with metal conduit is permissible, but the continuity of the metal sheath is lost, which in some cases violates earthing and shielding. Ventilated glands, which ensure pressure equalisation in sealed enclosures, are usually made of brass, as they require precise mechanics and strength. Plastic versions of ventilated glands are rare. Terminal boxes and distribution boards are often equipped with plastic glands, since the housing of the boxes themselves is plastic and does not require metal coupling.

When to Choose a Brass Cable Gland

• Explosion hazard zones of classes 1 and 2, where a certified explosion-proof gland is required.
• Facilities with high vibration and mechanical loads: cranes, crushers, conveyors, ship equipment.
• Outdoor installation in a marine or industrial climate with salt fog and UV radiation.
• High temperatures above +100 °C, for example, near furnaces, heaters, steam lines.
• The need for reliable earthing and shielding through the metal gland body when using metal conduit.

When to Choose a Plastic Cable Gland

• Distribution plastic boxes, boards, terminal cabinets in dry heated rooms.
• Moderate climate with temperatures from −40 to +80 °C without sharp fluctuations.
• Facilities where lightness and low price are important, and mechanical loads are minimal.
• Environments with high humidity, but without aggressive chemicals: food production, warehouses, offices.
• Installation on plastic equipment housings, where a metal gland may cause galvanic corrosion or is simply inappropriate.

Typical Mistakes in Selection and Installation

• Installing a plastic gland in an explosion hazard zone without checking the certificate. Such a gland will not provide explosion protection and will lead to an accident.
• Overtightening a plastic gland during installation. The thread is stripped, the housing cracks, and the sealing is compromised.
• Using a brass gland with a plastic housing without coordinating materials. Different coefficients of thermal expansion may lead to weakening of the joint under temperature changes.
• Selecting a seal without taking into account the actual cable diameter. A ring that is too small will not compress the cable, a ring that is too large will let moisture through.
• Saving on a gland for metal conduit: a plastic gland does not ensure earthing continuity, which is dangerous for equipment with a metal sheath.
• Ignoring IP requirements outdoors: a gland without protection against UV and moisture quickly fails.

Frequently Asked Questions

What is the difference between a brass and a plastic cable gland?

A brass gland is stronger, withstands higher temperatures, is mandatory in explosion-proof versions and is better compatible with metal conduit. A plastic gland is lighter, cheaper, does not rust, but is limited in temperature and mechanical strength.

Can a plastic cable gland be used outdoors?

Yes, if the model has an IP68 protection degree and UV-stabilised polyamide. For long-term outdoor installation in a harsh climate, brass is more reliable.

Which gland to choose for an explosion hazard zone?

Only a brass explosion-proof cable gland with Ex d or Ex e marking and a TR CU 012/2011 certificate. Plastic explosion-proof glands are allowed only in special cases and not for all zone classes.

What do the threads M20, M25, M32 mean?

This is a metric thread with an outer diameter of 20, 25 and 32 millimetres respectively. The gland size is selected according to the hole in the housing and the cable diameter.

Can a plastic gland be used with metal conduit?

It is permissible, but not recommended if continuous earthing or shielding is required. For metal conduit, a brass gland is better suited, ensuring a metal contact.

How does a ventilated cable gland differ from a regular one?

A ventilated gland equalises pressure between the housing and the environment, preventing condensation and damage to seals. Such glands are more often brass, as they require precise mechanics and strength.

Conclusion

The choice between a brass and a plastic cable gland is determined by operating conditions, not only by price. Brass is strength, heat resistance, explosion protection and reliability in an aggressive environment. Plastic is lightness, low cost, corrosion resistance and ease of installation in domestic and moderate conditions. At explosion hazard productions, in a marine climate, at high temperatures, a brass gland is virtually non-alternative. In distribution boards, plastic boxes, dry rooms, a plastic one is quite sufficient. A mistake in selection results not only in loss of sealing, but also in the creation of dangerous situations, therefore the selection should be approached with account for specific conditions.