What cable thread specifications apply to explosion-proof telephones?

Mixing up thread types is the fastest way to destroy an expensive explosion-proof casting. Forcing an NPT ¹ gland into a Metric ² hole (or vice versa) ruins the flamepath ³ threads, rendering the device unsafe and uncertifiable.

The global standard for explosion-proof telephones is Metric (M20 x 1.5 or M25 x 1.5) and NPT (1/2" or 3/4"). G-thread (BSP) is rarely used directly for Ex d entries due to sealing limitations. You must specify the entry type at the time of order to ensure the housing is machined correctly.

The "Tower of Babel" in Threads

At DJSlink, we serve the world.

• Europe/Asia/Australia: Almost exclusively Metric (M20).

• Americas (USA/Canada): Almost exclusively NPT (1/2" or 3/4").

• The Danger: An M20 bolt will screw into a 1/2" NPT hole for a few turns, then strip the threads. This destroys the equipment.

Are entries M20/M25, NPT 1/2", or G 3/4" available?

We machine the housing to suit your local installation standard.

Yes, the most common options are M20 x 1.5 (standard for telecom cables) and 1/2" NPT or 3/4" NPT (standard for conduit systems). M25 is used for thicker armored cables. G-threads (Parallel Pipe) are generally not offered for Ex d flameproof entries because they lack the thread engagement length required for flame cooling.

Selecting the Right Size

• M20 / 1/2" NPT: Adequate for standard LAN cables (CAT6) or 2-core power cables.

• M25 / 3/4" NPT: Required if you are using thick "Steel Wire Armored" ⁴ (SWA) cables. The gland for these cables is physically larger.

• Quantity: Most DJSlink phones come with 2 entries (one for power, one for network/signal) or 3 entries (allowing for daisy-chaining).

Do glands match thread type, IP, and Ex certification?

You cannot mix and match. The gland is a certified component that becomes part of the enclosure.

Absolutely. The cable gland must match the thread type (Metric/NPT), the IP rating (IP66), and the Ex protection method (Ex d or Ex e). Using a thread adapter is possible but introduces another leak path; direct matching is always preferred.

The Triple Match Rule

1. Thread: M20 Gland -> M20 Hole. (Don’t use tape to fix loose fits!)

2. Protection: Ex d Phone -> Ex d Gland.

3. Material: Stainless Phone -> Stainless/Nickel-Plated Gland. (Avoid galvanic corrosion ⁵).

DJSlink Pro Tip: We strongly recommend ordering the glands with the telephone. We supply them pre-fitted or in the box, guaranteed to match.

Are adaptors and stopping plugs certified accessories?

What if you have a 3/4" cable but a 1/2" hole? Or an unused hole?

Yes, thread adaptors (reducers/enlargers) and stopping plugs (blind plugs) are critical, certified accessories. They must carry their own ATEX/IECEx certificate. You cannot use a generic bolt to plug a hole; it must be a certified Ex d/Ex e stopping plug that engages at least 5 full threads.

The "Unused Entry" Rule

• The Hazard: An open hole is a direct path for an explosion.

• The Fix: Every unused entry MUST be plugged.

• The Plug: Must be certified. Plastic shipping plugs (red/blue caps) are for transport only. They must be removed and replaced with certified metal stopping plugs ⁶ before commissioning.

What torque values ensure flamepath integrity?

Loose glands leak gas. Overtightened glands crack threads.

Torque values are specified in the instruction manual (typically 25-40 Nm for metal threads). For Ex d, the gland must be fully tightened to ensure at least 5 full threads are engaged (for Metric) or wrench-tight (for NPT) to guarantee the mechanical strength of the flamepath and the compression of the IP sealing washer.

The "5 Thread" Rule

For Metric threads (Parallel):

• Requirement: At least 5 full threads must be engaged to cool the flame.

• Washer: A sealing washer ⁷ (nylon/fiber) is usually required between the gland shoulder and the housing face to maintain IP66.

• Torque: Tighten until the washer is compressed, then apply the specified torque to lock it.

For NPT threads (Tapered):

• Requirement: Wrench tight. The taper creates the seal and the flamepath.

• Sealant: Non-setting thread lubricant is advised to prevent galling ⁸ (seizing) on stainless steel.

Conclusion

Threads are the interface between your site and our safety device. Metric (M20) and NPT (1/2") are the standards. Always specify your preference to avoid using adapters. Ensure every gland matches the certification (Ex d/Ex e) and that every unused hole is sealed with a certified stopping plug. When in doubt, consult the manual for the correct torque—your safety depends on that seal holding tight.

Footnotes