M/PG/NPT Type Cable Gland: What You Should Know?

In electrical system reliability, cable glands are both critical and often overlooked. M, PG, or NPT thread standards not only determine compatibility but also affect sealing performance, environmental protection, and regulatory compliance. Choosing the wrong type can lead to costly downtime, safety hazards, or inspection failures. For example, high-voltage cable gland explosions can occur due to mismatched cable gland sizes and poor sealing.

In this guide, we will provide a detailed overview of M/PG/NPT cable glands: their core differences, applications, selection criteria, and best installation practices.

What Are M/PG/NPT Type Cable Glands?​

Cable glands (or cable connectors) are used to secure and protect cables, preventing damage as they enter enclosures, equipment, or bulkheads.

Their main functions include:

• Preventing cable damage due to pulling, twisting, or vibration.
• Providing dust, water, chemical, and moisture-resistant sealing.
• Ensuring compliance with industry standards.
• Providing grounding or electromagnetic interference shielding.

M, PG, and NPT refer to thread standards, the mechanical means used to connect the gland to the equipment. These standards vary by region and industry, so understanding their nuances is crucial.

What Are The Differences Between M, PG, And NPT Cable Glands?

M Series (Metric Thread)

Standard: M threads conform to ISO 2999/8380 standards, representing the global gold standard for metric applications and widely used in Europe, Asia, Australia, and most international markets.

Thread Characteristics: Straight thread (parallel thread), 60°angle, dimensions expressed as nominal diameter plus pitch. Sealing is achieved with an O-ring or gasket.

Materials and Sizes: Available in brass, stainless steel, or high-grade nylon. Sizes range from M8 to M63, with M20x1.5 being the most common size.

PG Series (Armored Thread)

Standard: Armored cable glands were developed in Germany and were originally designed for armored cables in heavy industrial environments.

Thread Characteristics: 60° straight thread with a coarse pitch. M series. Size markings use “PG” followed by a number, corresponding to the cable entry diameter. Sealing requires the use of an O-ring/gasket.

Materials and Sizes: Common materials include nickel-plated brass and stainless steel. Common sizes: PG11, PG16, PG21.

NPT Series (American National Standard Tapered Pipe Thread)

Standards and Source: The NPT standard is defined by ANSI/ASME B1.20.1 and is the North American pipe thread standard, used in the United States, Canada, and parts of South America.

Thread Characteristics: Tapered 60° thread with flat root and crest. It is self-sealing when tightened, but usually requires reinforcement with PTFE tape or pipe sealant. Size markings are based on pipe diameter.

Materials and Sizes: Brass, stainless steel, or galvanized steel. Sizes range from 1/8” NPT to 2” NPT.

Reference: M/PG/NPT Comparison Table

How To Choose The Right Cable Gland Type?

Matching the Enclosure Thread

If your enclosure has an M20 threaded hole, use an M20 cable gland. If it has a 1/2-inch NPT interface, choose an NPT cable gland. Mismatched threads can lead to loose connections, moisture ingress, and equipment damage.

Matching the Cable Diameter

Cable glands have specific cable diameter ranges. Using a cable gland that is too large or too small for the cable will result in poor sealing. For example, using a 95mm² cable gland with a 70mm² cable will cause problems.

Considering Environmental Conditions

• Wet/Outdoor Environments: NPT or IP68/IP69K rated M/PG cable glands, suitable for high-pressure washing.
• Corrosive Environments: Stainless steel (316L) cable glands.
• Hazardous Areas: Explosion-proof cable glands compliant with IEC 60079 standards.
• Extreme Temperatures: Cable glands with a temperature rating of -60°C to +100°C (stainless steel or silicone gaskets).

Ensuring Compliance with Regulatory Requirements

• Global Projects: IEC standards.
• Europe: ATEX, IECEx, CE certification.
• North America: UL certification.
• Marine Applications: DNV/ABS certification.

What Should You Pay Attention To When Installing Cable Glands?

M/PG Type Connectors (Straight Thread)

• Clean the housing threads to remove dust, debris, or other foreign matter.
• Apply thread lubricant to reduce wear and prevent seizing.
• Install the O-ring/gasket onto the connector flange.
• Tighten by hand first, then tighten another ¼ turn with a wrench. Do not overtighten, as this will crush the gasket and reduce sealing performance.
• Tighten the compression nut to secure the cable; the cable should be free of any looseness after tightening.

NPT Type Connectors (Tapered Thread)

• Wrap PTFE tape clockwise around the male thread.
• Tighten by hand first; the tapered threads will self-align during tightening.
• Tighten 1-2 turns with a wrench.
• Tighten the compression nut until it is securely sealed around the cable sheath/insulation.

Common Mistakes to Avoid

• Do not mix M and PG type threads; they are not interchangeable (different pitch and size).
• Do not omit the O-ring or thread sealant; this will compromise the IP rating of the housing and lead to leaks.
• Do not overtighten, as this can cause the housing to crack, the threads to strip, or the sealing surface to deform.
• Properly seal (plug) unused openings with certified sealing plugs. Open or poorly sealed holes can allow moisture ingress and pose a risk of electrical leakage/short circuits.

What Are The Development Trends For Cable Glands?

The main development trends for cable glands are driven by stricter safety/EMC requirements, harsher environments, and the need for faster installation:

1) Increased focus on standards and compliance

Manufacturers are aligning designs and testing with widely used cable gland requirements and test methods, particularly with regard to the IEC 62444 standard.

2) Growing demand for EMC cable glands in noise-sensitive systems

With the expansion of automation, drives, instrumentation, and high-speed communication, there is a growing demand for EMC cable glands that provide reliable 360° shielding contact, a wider range of applications, and more certifications.

3) Expansion of hazardous area solutions (ATEX/IECEx)

Increased electrification in oil and gas, chemical, and other hazardous locations is driving the application of explosion-proof cable glands and providing more configuration options suitable for zone-classified installations and standard compliance.

4) Hygienic design in the food, beverage, and pharmaceutical industries

In factories requiring washdown and strict hygiene, cable glands are increasingly following hygienic design principles, using stainless steel or suitable polymer materials, and obtaining certifications/approvals for hygienic environments.

5) Higher sealing performance in harsh environments

The demand for higher protection ratings and more robust sealing systems is expected to continue to grow to withstand environments such as outdoor exposure, washdown, vibration, and temperature cycling, often without increasing the size of the gland body.

6) Faster installation and fewer parts

End-users want faster and less error-prone installation. This is closely linked to meeting standardized performance tests and reducing field failures.

What Are The Answers To M/PG/NPT FAQ?

Question 1: Are M-type and PG-type cable glands interchangeable?

No. Their thread pitches and sizes are incompatible (for example, an M20x1.5 thread cannot be installed into a PG16 hole).

Question 2: Do NPT cable glands require sealant?

Yes, tapered threads require PTFE tape/pipe sealant to seal the gaps. Some NPT connectors come with O-rings, but sealant is recommended in wet environments.

Question 3: Which cable galnd type is best for global projects?

Series (metric) is universally used. For North American equipment, use NPT; for European machinery, PG-type connectors may be required.

Conclusion:

M/PG/NPT cable glands may seem like small components, but they’re the first line of defense for electrical systems. By understanding their differences, matching them to your enclosure/cable, and following installation best practices, you’ll ensure safety, compliance, and reliability.

Need help selecting the perfect M/PG/NPT cable gland for your project? Our technical team offers free advice. Contact us today or download our Cable Gland Sizing Chart for quick reference. Don’t let a wrong thread standard derail your project!