What is a Cord Grip
What is a Cord Grip
A cord grip is a mechanical device designed to secure, strain-relieve, and seal cables or wires as they enter electrical enclosures, equipment, or junction boxes. These essential components provide protection at cable entry points while maintaining the integrity of electrical connections. Often referred to as cable glands in some regions, they serve as critical interface points that prevent cables from being pulled out of their terminations while also providing environmental protection.
Components of Cord Grips
Modern cord grips consist of three primary components that work together to create a secure, sealed connection:
Body (Housing/Frame)
The body forms the main structure of the cable entry device and houses all other components. Typically manufactured from durable materials like metal or high-strength polymers, it provides the primary mechanical strength. The body features external threads designed to match specific thread standards for installation into equipment enclosures.
Sealing Nut (Cap Nut/Dome Cap)
The sealing nut is the adjustable component that compresses the internal seal when tightened. It threads onto the body and applies consistent pressure to create the gripping action. When properly tightened, it forces the internal seal to conform around the cable, creating both mechanical retention and environmental sealing.
Internal Seal (Grommet/Bushing/Sealing Insert)
The internal seal is arguably the most critical component, typically made from elastomeric materials like neoprene, silicone, or EPDM rubber. This flexible component deforms under compression to create a watertight seal around the cable while simultaneously providing the gripping force that prevents cable movement.
How Cord Grips Work
Electrical cord grips operate through two primary mechanical functions that work in tandem:
Sealing
When installed correctly, cord grips create environmental barriers that prevent ingress of water, dust, and contaminants. As the sealing nut is tightened, the internal seal deforms and compresses around the cable jacket, creating a watertight connection.
Clamping/Gripping
Beyond environmental protection, cord grips provide crucial strain relief by mechanically securing cables. The compression force applied by the sealing nut creates sufficient friction between the internal seal and cable jacket to prevent cable movement or pullout.
Cord Grip Materials
The performance characteristics of cord grips are largely determined by their construction materials, which are selected based on application requirements:
Plastics
- Nylon (Polyamide): Offers excellent chemical resistance, high tensile strength, and electrical insulation properties. Typically rated for temperatures between -40°C to +105°C, nylon cord grips provide cost-effective solutions for general-purpose applications.
- PVC (Polyvinyl Chloride): Provides good corrosion resistance and electrical insulation at a lower cost point. PVC options typically have a more limited temperature range of -20°C to +80°C but offer sufficient protection for many indoor applications.
Metals
- Brass (often Nickel-Plated): Combines excellent corrosion resistance with good machinability and electrical conductivity. Nickel-plated brass offers enhanced chemical resistance and is commonly used in marine and industrial environments.
- Stainless Steel (Grades like 303, 304, 316/316L): Provides superior corrosion resistance, particularly in harsh environments.
- Aluminum (often Nickel-Plated): Offers significant weight reduction compared to brass or steel while maintaining good corrosion resistance and electromagnetic shielding properties when plated.
- Steel (often Galvanized or Nickel-Plated): Provides high mechanical strength and durability at a lower cost than stainless steel or brass. Protective coatings prevent corrosion while maintaining the material’s inherent strength advantages.
Thread Standards
NPT (National Pipe Thread)
The American standard NPT thread features a tapered profile that creates a seal through thread deformation. Common in North American industrial applications, NPT threads are measured in inches with typical sizes ranging from 1/8″ to 2″. The tapered design provides a mechanical seal without additional sealing compounds in many applications.
Metric (ISO Metric)
Metric threads follow the International Organization for Standardization specifications with straight threading measured in millimeters. These parallel threads are common throughout Europe and Asia, requiring sealing washers or O-rings to achieve environmental protection. Typical sizes range from M12 to M63, with the number representing the nominal outside diameter in millimeters.
PG (Panzer-Gewinde)
Originally developed in Germany, PG threads are designated by nominal size rather than actual dimensions (e.g., PG11, PG16). While less common in new installations, legacy equipment often requires PG-threaded cord grips for replacement or maintenance purposes. These threads feature a parallel profile with a 1/6-inch thread pitch.
ISO
ISO thread standard provides uniform specifications for worldwide interchangeability. Featuring parallel threading with standardized tolerances, ISO threads facilitate global equipment compatibility and simplified inventory management. The specification includes detailed tolerance classes for both internal and external threads.
G (BSPP – British Standard Pipe Parallel)
G-threads, also known as BSPP, feature parallel threads with a 55° thread angle. Measured in inches despite their parallel profile, these threads require additional sealing methods such as washers or O-rings. Common in British Commonwealth countries and parts of Europe, they offer reliable connections when properly sealed.
Types of Cord Grips
Cord grips are available in various configurations to accommodate different installation requirements:
Straight
The most common configuration features a linear design where the cable enters and exits along the same axis. This design minimizes space requirements and provides the simplest installation method for most applications. Straight cord grips typically offer the highest ingress protection ratings and pull-out resistance due to their optimized internal geometry.
90° (Right-Angle)
Right-angle cord grips redirect cables at a 90-degree bend, ideal for installations with limited space or where cables must run parallel to mounting surfaces. This configuration reduces stress on cables in tight installations by eliminating sharp bends that could damage conductors or compromise jacket integrity. The design typically incorporates reinforced construction at the bend to maintain environmental protection.
45° Angle
A compromise between straight and right-angle configurations, 45-degree cord grips provide moderate direction change while maintaining good pull-out resistance. This design accommodates installations where cables approach enclosures at an angle, reducing cable stress without requiring the full space needed for a 90-degree bend. Industrial applications often utilize these configurations where vibration or movement could stress cable connections.