What does an ATEX marking such as II 2G Ex db IIC T6 Gb mean?

II is equipment group II (not mining). 2G is category 2 for gas, suitable for Zone 1. Ex db is a flameproof enclosure suitable for Zone 1. IIC is the most demanding gas group, which includes hydrogen. T6 means a maximum surface temperature of 85 °C. Gb is the equipment protection level for Zone 1. Every element must suit the location where the part is installed.

What is the difference between ATEX, UKEX and IECEx?

ATEX Directive 2014/34/EU governs equipment for explosive atmospheres placed on the EU market. Great Britain implements it through the EPS Regulations 2016, which is where UK marking applies. IECEx is an international certification scheme based on type testing and factory quality assessment; a product is IECEx certified only if it appears on the IECEx online certificate system. Many products carry more than one.

Can I use an industrial servo motor or actuator in a hazardous area?

Not in a classified zone unless it is certified for that zone, gas group and temperature class, or installed inside a certified protective enclosure or pressurised cabinet. Standard industrial parts are fine in safe areas, such as on a non-hazardous skid, in a pressurised equipment room or on test rigs. Always check the zone drawing before specifying.

What is an electric choke actuator?

An electromechanical actuator that positions a drilling choke valve to control back-pressure, for example in managed pressure drilling, where it controls the pressure of mud returning to surface. Electric chokes replace hydraulic or manual operators for faster, more precise control. Tolomatic's ServoChoke SVC is one published example, certified for Class I Division 1, ATEX and IECEx.

Which slip ring suits a hazardous area?

A flameproof (Ex d) or otherwise certified unit, or a standard slip ring inside a certified enclosure. Check the marking: a unit marked Ex d IIB T4 Gb suits Zone 1 and 2 with group IIA and IIB gases at T4, but not hydrogen or acetylene (group IIC). FPSO turret swivels use Ex d, Ex de or Ex p protection.

What should I send for an oil and gas enquiry?

Send the hazardous-area zone, gas group and temperature class from the area classification, the certification required (ATEX, UKEX, IECEx, Class/Division), force, stroke, speed and duty or circuits and speed for a slip ring, process pressure and temperature, ambient range, ingress rating, supply voltage, fail-safe position, and for downhole tools the temperature, pressure and envelope.

ATEX actuators, explosion-proof motors and slip rings

Specify Motion technical library · Updated 30 October 2026 · How we prepare our content

In short:Oil and gas motion components are chosen by hazardous-area certification first and performance second: a choke actuator, motor or slip ring in Zone 1 must carry ATEX, UKEX or IECEx certification for the right equipment category, gas group and temperature class, such as Ex db IIB T4 Gb. Downhole parts add temperatures to 200 °C or more and pressures to 1,700 bar.

Typical requirements

Zone 0 / 1 / 2 (gas)	Equipment category 1G / 2G / 3G; EPL Ga / Gb / Gc
Gas groups	IIA (propane), IIB (ethylene), IIC (hydrogen)
Temperature classes	T1 450 °C, T2 300 °C, T3 200 °C, T4 135 °C, T5 100 °C, T6 85 °C maximum surface
Flameproof slip ring (example)	Ex d IIB T4 Gb, up to 100 A per circuit, 50 rpm, -45 to +135 °C
Downhole slip rings (example)	200 °C standard, 230 °C option, 25 kpsi (1,700 bar), oil-filled
Electric MPD choke actuator (example)	Certified for Class I Div 1, ATEX and IECEx (Tolomatic ServoChoke)

Machinery we specify motion for

Managed pressure drilling chokes
Choke and kill valve control
Topside valve actuation
Rig cable reels and spooling
Drilling equipment and top-drive services
Downhole tools and MWD
Pipe-crawler inspection
Explosion-proof process machinery

Why hazardous-area certification comes first

On drilling rigs, production platforms, FPSOs, terminals and refineries, much of the plant is classified as a hazardous area. In Great Britain, HSE explains that two frameworks apply: DSEAR (implementing ATEX Directive 99/92/EC) requires employers to classify zones, and the Equipment and Protective Systems Regulations 2016 (implementing Directive 2014/34/EU) govern the equipment that goes into them. They apply to electrical and mechanical equipment alike. Certified equipment carries the “Ex” symbol, and most categories need third-party certification by a conformity assessment body.

For a motion component that means the first question is not force or torque but where the part sits and what certification it carries. A brilliant actuator with no Ex certificate cannot go in Zone 1.

Decoding zones, gas groups and temperature classes

R. STAHL’s Ex marking guide sets out the mapping:

Zone (gas)	Equipment category	EPL	Typical protection types
Zone 0	1G	Ga	ia (intrinsic safety), da
Zone 1	2G	Gb	db (flameproof), eb (increased safety), ib, p (pressurised)
Zone 2	3G	Gc	dc, ec, ic, n types

Gas group	Example gas	Note
IIA	Propane	Least demanding
IIB	Ethylene	Also covers IIA
IIC	Hydrogen	Most demanding; covers IIB and IIA

Temperature classes set the maximum surface temperature: T1 450 °C, T2 300 °C, T3 200 °C, T4 135 °C, T5 100 °C, T6 85 °C. The equipment’s class must be below the auto-ignition temperature of the gases present. Flameproof enclosures (d) are used for motors and switchgear, increased safety (e) for terminals and squirrel-cage rotors, intrinsic safety (i) for sensors, pressurisation (p) for cabinets and large motors.

Internationally, the IECEx Certified Equipment Scheme certifies equipment by type testing and factory quality assessment, with ongoing surveillance. If a product is not on the IECEx online certificate system, it is not IECEx certified, so check the certificate number rather than a brochure.

Where motion components sit in oil and gas

Equipment	Motion	Components and certification issues
MPD and drilling chokes	Linear positioning of the choke	Certified electric actuator, position encoder, safe-area drive
Choke and kill, topside valves	Linear or quarter-turn	Electric actuator or gearmotor, fail-safe position
Rig cable reels	Slow, reversing rotation	Ex slip ring, certified motor, level-wind
Drilling equipment	Rotation with services	High-current or Ex slip rings, rugged encoders
FPSO turrets	Vessel rotates about turret	Ex d, Ex de or Ex p electrical swivels
Downhole tools and MWD	Rotation at high temperature and pressure	Oil-filled HTHP slip rings, high-temperature motors and encoders
Pipe crawlers	Traction and camera motion	Sealed gearmotors, certified where the pipe atmosphere requires

Electric choke actuators for managed pressure drilling

In managed pressure drilling, the choke controls the pressure of mud flowing back to surface. Tolomatic describes its ServoChoke SVC as an electric rod-style choke valve actuator for precision control of that pressure, also used in choke and kill installations, and certified for Class I Division 1, ATEX and IECEx. The same page positions its RSA rod actuators for valve actuation and for replacing pneumatic and hydraulic cylinders. The general case for electric chokes is precise, repeatable positioning, simple remote control and no hydraulic power unit; see our hydraulic to electric actuator guide.

Slip rings for rigs, reels and FPSOs

A flameproof slip ring in our range is marked Ex d IIB T4 Gb. Read against the tables above, that means a flameproof enclosure for Zone 1 (and Zone 2), group IIB and IIA gases, and a maximum surface temperature of 135 °C. It is not suitable for hydrogen or acetylene (IIC) atmospheres. It carries up to 100 A per circuit at up to 50 rpm with an operating range of -45 to +135 °C, which suits rig reels and slow rotating process equipment.

Moog’s slip ring product guide shows the extremes. FPS swivels for FPSO turrets use Ex d, Ex de or Ex p protection and reach 145 kV on high-voltage units. Downhole model 303 slip rings are built for high-temperature, high-pressure service, generally oil-filled, rated 200 °C standard and up to 230 °C, at 25 kpsi (1,700 bar), with up to 600 rpm on the miniature-bore version. Moog describes its oil and gas work as motion control, surveillance and data communication for long life in extreme and hazardous environments. See rugged slip rings, high-current slip rings and slip rings for cable reels.

Safe area, protected enclosure or certified part?

There are three ways to put motion into a hazardous plant, and the choice shapes the whole design:

Keep it out of the zone. Mount drives, controllers and standard motors in a safe area or a pressurised room and transmit motion mechanically, or move the equipment boundary. Often the cheapest route when it is possible.
Put standard parts inside a certified enclosure. A flameproof or pressurised housing around a standard actuator or slip ring. The certification then belongs to the assembly, which must be assessed as a whole.
Use certified components. Ex-certified motors, actuators, slip rings and sensors installed directly in the zone. Simplest to install, but the choice of parts is narrower and lead times are longer.

Downhole tools: heat, pressure and oil-filled designs

Downhole tools and measurement-while-drilling equipment run at temperatures and pressures far beyond surface plant. Moog’s downhole slip ring figures, 200 to 230 °C and 1,700 bar, show the scale. Moog describes its downhole slip rings as generally configured for an oil-filled environment, and motors, encoders and electronics are built from high-temperature materials. Envelope is tight, because everything must fit inside a slim tool string. Ask suppliers for rated temperature and pressure, the fill fluid, life at temperature, and shock and vibration test levels.

Worked example: sizing an electric choke actuator

Assume a choke with a 25 mm stem, a worst-case unbalanced pressure of 34.5 MPa (5,000 psi) and 2 kN of packing friction. All figures are illustrative.

Stem area: π × 12.5² ≈ 491 mm².
Pressure force: 491 mm² × 34.5 N/mm² ≈ 16.9 kN.
Total force: 16.9 + 2 ≈ 18.9 kN. Add a 1.5 margin for pressure spikes and wear: about 28 kN.
Speed: decide the full-stroke time the pressure control loop needs; that sets the screw lead and motor speed.
Certification: if the choke manifold is in Zone 1 with group IIA gases, the actuator needs at least category 2G, IIA and a temperature class below the gas’s auto-ignition temperature, for example Ex db IIA T4 Gb or better.
Fail-safe: define the position on power loss (hold, open or close) and how it is achieved.
Feedback: absolute stem position, inside the certified enclosure or as a certified sensor.

Typical pitfalls

Specifying from a datasheet without the zone drawing. The area classification decides the certification.
Wrong gas group. IIB equipment is not acceptable where hydrogen is present.
Ignoring temperature class at full load. Motor and brake surfaces heat up with duty.
Assuming mechanical parts are exempt. The EPS Regulations cover mechanical equipment too.
Long motor cables from a safe-area drive without checking voltage reflection and motor temperature.
Certificates not checked on the IECEx system or with the notified or approved body.

What to send an engineer

Send the zone, gas group and temperature class, required certification, force, stroke, speed and duty (or circuits, speed and bore for a slip ring), process pressure and temperature, ambient range, ingress rating, supply, fail-safe position and design life. Our engineers can then propose certified or safe-area components that fit, and say clearly which is which.

Slip rings for oil and gas and hazardous areas

Rotating equipment on rigs and process plant needs power and signals across continuous rotation: cable and hose reels, drilling equipment, rotating process machinery and turret swivels. In a classified zone the slip ring must be certified, for example a flameproof unit marked Ex d IIB T4 Gb, or sit inside a certified enclosure. Heavy carbon-brush units carry hundreds of amps for rig and port machinery; high-temperature units cover hot plant. Specify zone, gas group and temperature class, circuits with voltage and current, speed, bore, ingress rating and ambient range.

Rig cable reels: power and control at the drum in hazardous areas
Drilling platforms: high-current rotating equipment
Process machinery: flameproof slip rings for Zone 1 and 2
Hot plant: high-temperature slip rings