Custom Cable Entry for Explosion-Proof Servo Motors – Flexible Wiring Made Simple with Wheatstone

In explosion-proof servo motor selection, cable entry is often the last thing considered—yet it causes the most on-site headaches. A standard motor has only one fixed cable entry orientation. But when the junction box position on the equipment doesn’t align, when the cable gland direction is wrong, or when the motor needs to fit into a cramped space, the result is either remachining flameproof threads or adding intermediate junction boxes. Worse, when power, encoder, and brake cables are bundled together, a single faulty cable means disconnecting everything. Almost every field engineer has experienced this frustration.

I. Why Cable Entry Cannot Be “Compromised”

The cable entry device is the transition point where external conductors enter the explosionproof equipment. It is in direct contact with the surrounding explosive gas mixture and is the weakest link in explosionproof electrical equipment—its sealing performance directly affects operational life, reliability, and explosion safety. Consequently, national standard GB/T 3836.1-2021 imposes stringent requirements on sealing, protection rating matching, and installation methods.

An incompatible cable entry can lead to:

Seal failure: Excessive cable bending or uneven gland loading deforms the sealing ring, allowing flammable gas ingress.

Difficult maintenance: All cables exiting through a single opening makes fault identification hard, multiplying troubleshooting time.

Space conflicts: The junction box location interferes with adjacent equipment, forcing onsite thread modifications that risk safety.

Increased losses: Extended cables cause voltage drop and encoder signal interference, degrading control accuracy.

II. Common Cable Entry Methods for ExplosionProof Servo Motors

Depending on protection type and application, several cable entry methods are available:

1. Standard Junction BoxThe motor is equipped with a flameproof (Ex d) or increased safety (Ex e) junction box. Onsite, cables are introduced via explosionproof cable glands and connected to internal terminals. Increased safety terminal boxes are made of highstrength materials with arcresistant, hightemperature insulation terminal strips, offering at least IP54 protection. This method is versatile but requires more space and longer installation time.

2. Direct Cable ExitThe motor has factoryattached cables that are sealed onsite using explosionproof glands or filling compounds. Eliminating the junction box shortens the motor’s axial length, making this ideal for spaceconstrained installations. However, cable repair is more complex.

3. **Aviation Plug (QuickConnect)**The motor integrates an explosionproof aviation socket, paired with a prefabricated cable. Onsite, the installer simply inserts the plug and tightens the locking nut—electrical connection and sealing are completed in seconds. This method dramatically shortens installation time, reduces wiring errors, and is particularly suitable for batch installations and frequent disconnections. Encoder signals can be routed through dedicated pins to minimize interference.

4. Independent MultiCable ExitPower, encoder feedback, brake control, and temperature sensor signals are routed through separate cables, each with its own gland. This approach is widely used in highreliability applications such as chemical and pharmaceutical plants. In one application where three explosionproof servo motors were used, independent multicable exit greatly simplified field wiring and made maintenance much faster.

5. Terminal Block DistributionA terminal block inside the motor’s junction box allows a single main cable to enter, then power, encoder, and brake signals are distributed internally. This reduces the number of external cables and glands, resulting in a cleaner, more organized installation.

III. Wheatstone’s FourStep Customisation Logic

Jiangsu Wheatstone offers “oneclient, onesolution” customisation, truly enabling motorbymotor tailoring-. For cable entry customisation, the logic follows four steps:

Step 1: Determine the Explosion Protection Type

Gas Zones 1 & 2: Prefer Ex d flameproof or Ex e increased safety junction boxes.

Dust Zones 21 & 22: Select Ex tb dustignitionproof junction boxes with IP65/IP67.

Mixed gas and dust: Choose dualcertified junction boxes.

Step 2: Specify Cable Type and Size

Standard rubber cables: Use sealing ring type glands.

Armoured cables: Require special armoured cable glands with effective armour grounding.

Cable outer diameter must precisely match the gland’s sealing ring.

Step 3: Define Cable Exit Direction and Position

Axial exit: Cables exit along the motor’s rear axis—suitable when axial space is available.

Radial exit: Cables exit from the motor side; multiple angles (90°, 180°) are available to suit different junction box positions.

Multidirection exit: The motor can be prepared with several entry ports; unused ports are sealed with certified Ex blanking elements.

Step 4: Define Signal Grouping

Separate power cables from encoder signal cables to avoid electromagnetic interference.

Brake control and temperature sensor cables may be routed independently or integrated.

For multiaxis systems, an aviation plug can integrate all signals for a “plugandplay” installation.

IV. Technical Advantages of Wheatstone’s Custom Cable Entry

1. Full Explosion Protection CoverageWheatstone motors hold Class I Coal Mining Safety, Class II Gas ExplosionProof (Ex d IIB T4 Gb / Ex db IIC T4 Gb), Class III Dust ExplosionProof (Ex tb IIIC T130℃ Db), as well as IECEx and ATEX certifications. Junction boxes and cable entry devices are certified to the same protection level as the motor itself—no safety gaps.

2. High Ingress ProtectionJunction boxes and cable entry devices achieve IP65/IP67, resisting dust, oil, and highpressure water washdown. Suitable for chemical plants, pharmaceutical workshops, and outdoor environments.

3. Sealing Ring Type EntryStandardised sealing ring type cable glands are used. Installation requires only tightening the compression element with a tool (at least five threads engaged), ensuring the cable jacket passes fully through the device and is clamped securely against the sealing ring—preventing loosening or pullout. Simple, reliable sealing.

4. Wide Interface Options

Metric threads: M20×1.5, M25×1.5, M32×1.5, etc.

NPT threads: 1/2″ NPT, 3/4″ NPT, etc.

Flanged interfaces: For large crosssection cables.

Aviation plug interfaces: Multipin integrated for quick connection.

1. Signal Integrity ProtectionEncoder signal cables are routed separately from power cables using dedicated shielded cables and glands, effectively suppressing electromagnetic interference and ensuring stable highprecision position feedback.

V. RealWorld Case: Chemical Plant Vision Inspection System

A chemical plant in East China needed a vision inspection system for precise positioning with an error tolerance of 0.02 mm (2 si). The customer selected three Wheatstone 400W 1.3 Nm explosionproof AC servo motors with absolute encoders (position memory required), Siemens PLC as the host, and 485 communication.

Cable entry challenges:

Motors mounted in a cramped inspection cabinet; standard junction boxes could not fit.

Encoder signals, power, and communication cables needed separate routing to avoid interference.

Tight commissioning schedule demanded fast field wiring.

Wheatstone custom solution:

Aviation plug cable entry: motors fitted with explosionproof aviation sockets and prefabricated multicore cables.

Encoder signals independently shielded and routed separately from power.

Batch customisation delivered in 7 days; onsite installation time reduced by approximately 60%.

After the retrofit, positioning accuracy remained within 0.02 mm, and the system has operated faultfree for 18 months. Customer feedback: “Wiring used to take half a day. Now it’s plug, twist, and done in ten minutes. Maintenance is much easier too.”

VI. Cable Entry Customisation Selection Reference

Application	Recommended Entry	Explosion Class	Ingress	Interface	Suitable For
Chemical vision inspection, precision positioning	Aviation plug (multipin)	Ex d IIB T4	IP65	M23/M40	Tight spaces, fast installation
Pharmaceutical filling, cleanrooms	Direct cable + gland	Ex e ib IIC T4	IP66	M20×1.5	Sterile, easyclean
Painting robots, reciprocators	Radial exit (90°)	Ex d IIB T4	IP67	3/4″ NPT	Internal cabling, paintproof
Underground mining	Armoured cable + special gland	Ex d I Mb	IP66	M25×1.5	High mechanical protection
Explosionproof AGVs, mobile equipment	Aviation plug (low voltage)	Ex d IIB T4	IP65	M12	Frequent disconnection, low voltage
Multiaxis systems	Terminal block distribution	Ex db IIC T4	IP66	Custom	Centralised control, easy maintenance

VII. Conclusion

Cable entry for explosionproof servo motors is never a onesizefitsall product. From selecting the explosion protection type to matching cable specifications, from defining exit direction to grouping signals—every detail affects onsite installation efficiency and longterm reliability.

With over two decades of expertise in specialty motors, Jiangsu Wheatstone offers permanent magnet motors covering frames from 40 mm to 400 mm, power from 50 W to 200 kW, and voltage from 24 V to 3000 V. Upholding the “oneclient, onesolution, motorbymotor” philosophy, we customise cable entry methods to your exact needs—from standard glandtype junction boxes to quickconnect aviation plugs, from singlecable exit to multicable distribution—delivering truly customised explosionproof servo motors.

For custom explosionproof servo motor requirements, contact the Wheatstone technical team for fullprocess support—from cable entry scheme design to onsite installation guidance.