Motor Protection in Potentially Explosive Atmospheres

Introduction

Gases, vapors, mists, or dusts mixed with air can form a flammable mixture, creating a potentially explosive atmosphere. Electrical equipment installed in such locations must be designed and tested to prevent electric arcs or high temperatures that could serve as an ignition source.

This brochure provides information on regulations, standards, definitions, and equipment requirements related to protective devices for motors in potentially explosive atmospheres.

Understanding Standards for Explosive Atmospheres

Globally, various regulations and certification systems exist with differing requirements. Technical requirements are increasingly harmonized with global IEC standards.

IECEx System

The IECEx System (www.iecex.com) of the International Electrotechnical Commission is a voluntary certification system that verifies conformity with IEC standards for safety in potentially explosive atmospheres. IECEx covers four main areas: certification of service facilities, IECEx equipment certification, Ex marking conformity, and personnel competency certification.

IECEx Mark of Conformity: For equipment to receive the "Ex" mark of conformity under IECEx, it must have a certificate of conformity, requiring an approved IECEx Quality Assessment Report (QAR) and an approved IECEx Test Report (ExTR). The IECEx mark confirms appropriate protection for use in hazardous areas (considering zone classification) and that the product was manufactured under a system with continuous supervision by certification bodies. It also indicates the product can be marketed without further testing.

European Directives (ATEX)

European regulations, commonly known as ATEX (from French "ATmosphères Explosibles" - explosive atmospheres), combine two EU directives: the directive on the health and safety of workers (1999/92/EC) and the product directive (2014/34/EU). EU directives differ slightly from IECEx and do not cover service facility or personnel competency certification. In EU countries, compliance with the "essential health and safety requirements" described in the directives is mandatory. The simplest way to demonstrate compliance is by adhering to harmonized standards.

Protective Devices

Protective devices are often a requirement of the IEC/EN 60079 series for the safe operation of Ex equipment. These devices can be located inside or outside hazardous zones. Protective devices for Ex equipment and products are covered by ATEX: the harmonized standard EN 50495:2010. IECEx lacks a mandatory standard for electrical safety devices for Ex equipment, so such certification can only be performed according to ATEX.

Key Standards Worldwide

Many countries have regulations for the design and use of electrical equipment in hazardous areas, but these may vary. Such regulations are increasingly harmonized within the framework of IEC recommendations and European standards. In some countries (e.g., Brazil, Australia, or Japan), national requirements may need to be met for final installation approval, although these national regulations generally correspond to one of the major standards listed below.

IEC and EN Standards

• IEC/EN 60079-0: Equipment – Basic requirements
• IEC/EN 60079-1: Equipment protection by flameproof enclosure "d"
• IEC/EN 60079-7: Equipment protection by increased safety "e"
• IEC/EN 60079-10: Classification of hazardous areas (gas zones)
• IEC/EN 60079-10-1: Classification of areas – Explosive gas atmospheres
• IEC/EN 60079-10-2: Classification of areas – Explosive dust atmospheres
• IEC/EN 60079-14: Electrical installations – Design, selection and erection
• IEC/EN 60079-15: Equipment protection by type of protection "n" (no longer applies to rotating machinery)
• IEC/EN 60079-17: Electrical installations – Inspection and maintenance
• IEC/EN 60079-19: Equipment repair, overhaul and reclamation
• IEC/EN 60079-31: Equipment protection by dust tight enclosure "t"

ATEX Directives

The directive on the health and safety of workers (1999/92/EC) defines "minimum requirements for the safety and health protection of workers likely to be exposed to risks from explosive atmospheres." The product directive (2014/34/EU) specifies requirements for equipment used in hazardous areas. It also includes requirements for "protective systems intended for use in potentially explosive atmospheres."

Besides IECEx and ATEX, several local standards may apply in specific countries.

Other Standards

IEC: International Electrotechnical Commission

EN: European Standard

NEC/CEC: National Electrical Code / Canadian Electric-Code (500 or 505) in North America

[Textual description of world map showing regional standards like IECEx, ATEX, NEC/CEC, Inmetro, SABS, UkrSepro, TR-CU/EAC, Korean Standard, TIIS, CNEX, ITRI, PESO, ANZEx]

Equipment Groups for Potentially Explosive Atmospheres

The international standard IEC/EN 60079-0 defines three groups of equipment for use in potentially explosive atmospheres, while the product directive specifies two groups based on the location of equipment use.

Groups

• Group I: Covers mines susceptible to firedamp.
• Group II: Refers to surface installations with gases.
• Group III: Refers to surface installations with dusts.

The ATEX product directive defines only two groups: Group I covers equipment intended for use in mines susceptible to firedamp and/or combustible dust, while Group II covers all surface installations.

The assignment of a group is primarily based on the intended location of use (equipment classification).

Subgroups and Temperature Classes

Explosive gases, vapors, and dusts have different chemical properties affecting the probability and force of an explosion. These properties include flame temperature, minimum ignition energy, upper and lower explosive limits, and molecular weight. Gases are assigned to groups IIA, IIB, and IIC, while dusts are assigned to IIIA, IIIB, and IIIC.

Temperature classes for equipment are defined by the maximum surface temperature of the equipment. When selecting equipment for a hazardous zone, the maximum surface temperature of the equipment must be considered, which should be lower than the ignition temperature of the potential gas or dust mixture.

Dust Classification

Internal Division of Dusts: IIIA (Combustible flyings), IIIB (Non-conductive dusts), IIIC (Conductive dusts)

Gas Classification

Internal Division of Gases:

• IIA: Approx. 120 gases and vapors, e.g., butane / petroleum / propane
• IIB: Approx. 30 gases and vapors, e.g., ethylene / dimethyl ether / coke oven gas
• IIC: Three gases: hydrogen (H₂) / acetylene (C₂H₂) / carbon disulfide (CS₂)

ATEX Directive Relationships

[Textual description of ATEX diagram showing relationship between worker protection directive (classifying zones, defining categories) and product directive (specifying equipment requirements for each category), and the concept of EHSR.]

Manufacturer Responsibility: The manufacturer is responsible for product safety and providing installation and maintenance instructions. The product directive guides the manufacturer in preparing product classification and certification.

End-User Responsibility: The end-user is responsible for ensuring the product is installed, maintained, and operated in a way that poses no explosion risk. The worker protection directive provides guidance for end-users on using certified products and developing risk analyses, safety instructions, training, and operating/maintenance procedures.

Zones, Categories, and Equipment

In industry, all potentially explosive spaces must be classified into hazardous areas, defining so-called hazardous zones.

Zones

The zone system is used worldwide and is also accepted as an alternative system in North America. Areas are typically defined by relevant authorities, external bodies, notified bodies, or other experts. The owner is responsible for ensuring their site is classified before selecting and installing appropriate products.

Globally, the zone system is used for classifying hazardous areas. These zones are defined by the worker protection directive and international standards IEC/EN 60079-10-x. In all cases, zone classification is the responsibility of the owner of the site where the hazardous zone is located.

There are six zones:

• Zones 0 (for gases) and 20 (for dusts): Where an explosive atmosphere is continuously present.
• Zones 1 (for gases) and 21 (for dusts): Where a potentially explosive atmosphere occurs occasionally.
• Zones 2 (for gases) and 22 (for dusts): Where a potentially explosive atmosphere may occur incidentally, but not during normal operation.

Equipment Groups and Zones according to IECEx and ATEX

[Textual description of diagram showing IECEx and ATEX group and zone classifications, e.g., Ex ec IIB/C T3 Gc, Ex tc IIIB/C T125°C Dc, Ex d(e) IIB/C T4-T6 Gb, Ex tb IIIB/C T125°C Db]

Equipment Categories

Equipment categories are used in the ATEX directive. A category indicates the required safety level for specific zones. Zone 0/20 requires Category 1 equipment, Zone 1/21 requires Category 2, and Zone 2/22 requires Category 3.

Category classification is crucial because end-user control, maintenance, and repair obligations depend on the product/equipment category, not just the zone of installation.

Equipment Protection Levels (EPL)

Recent changes in IEC and EN standards introduce "Equipment Protection Levels" (EPLs), which identify products based on the ignition risk they might cause. EPLs also consider the potential consequences of an explosion. For Zone 0/20, the required EPL would be "a"; for Zone 1/21, "b"; and for Zone 2/22, "c".

[Textual description of a diagram showing zone classification around a storage tank, indicating distances 'a', 'b', 'c' from ventilation opening, roof, and tank side respectively.]

Marking of Equipment According to IECEx and ATEX

There are two distinct markings for equipment compliant with IEC and EN standards, plus an additional marking according to the ATEX directive.

Equipment Protection Marking according to IEC and EN Standards

[Textual description of an example marking like "Ex db IIC T4 Gb"]

• Protection Type: Ex d (flameproof) with EPL b
• Equipment Group: II (gases) and internal division C (e.g., hydrogen)
• Temperature Class: T4 = max. permissible 135°C
• Equipment Protection Level: Level "b" for gases

Additional Marking according to ATEX Directive

[Textual description of an example marking like "CE 0081 II 2G"]

• CE Marking: European Commission mark for Ex products
• Notified Body Identifier: Identifier of the notified body responsible for approval
• Equipment Group: II for industrial surface applications
• Equipment Category: 2G for gas environments requiring a high level of protection

Safety Functions with ATEX Certification

According to the ATEX directive, protective devices are subject to certification and marking. The marking of a protective device can be found on the device it is integrated with.

The ATEX marking of a protective device refers solely to the safety function of that device. The marking does not indicate that the protective device has been tested and certified together with the motor. Protective devices are typically not equipped with an explosion-proof enclosure (Ex).

Therefore, protective devices must be located exclusively outside hazardous zones. In the ATEX conformity marking, this is indicated by parentheses around the equipment category number, e.g., (2).

[Textual description of an example protective device marking, showing ATEX and IECEx details, and explaining the meaning of parentheses.]

[Note: Parentheses indicate that the protective device can be used to protect products belonging to categories 2 and 3, excluding the protective device itself.]

Selection and Installation of Protective Devices in Hazardous Areas

When selecting motors with protective devices for operation in hazardous areas, follow the manufacturer's instructions and recommendations. Since only the motor can be installed in a hazardous zone, and protective devices must always be located in a safe zone, instructions aim to prevent motor overheating or sparking. For safe operation, specific considerations must be taken when selecting motors with protective devices.

Servicing and Maintenance

Regular servicing is essential for maintaining the safety of electrical systems in hazardous areas. Key safety measures include:

• Work on live electrical installations and equipment is prohibited in hazardous zones. An admissible exception: work on intrinsically safe circuits.
• Grounding or short-circuiting is permissible in hazardous zones only when there is no risk of explosion.
• During all work performed in hazardous zones, it is crucial to prevent the creation of sparks that could be an ignition source or excessive surface heating that could cause an explosion in the hazardous zone.

ABB Solutions for Motor Starting and Protection in Hazardous Areas

Many industrial control products, such as overload relays or motor protection circuit breakers, are designed for switching and controlling equipment in hazardous areas, even though the control gear itself is located outside such a zone. Such equipment is marked with the category of the protected electrical equipment, with the category enclosed in parentheses, e.g., B: Ex II (2) GD.

These types of protective devices are approved for equipment group II, category (2) in Zone "G" (zones with potentially explosive mixtures of gases, vapors, fumes, or air) and additionally in Zone "D" (zones with combustible dust). This protective device is not intended for installation or operation in hazardous zones. When using equipment in hazardous zones, preventive measures must be taken, such as ensuring appropriate enclosure.

ABB Product Range for Hazardous Areas

For more detailed information, visit: new.abb.com/low-voltage/products/explosion-protective-components-systems

Product Spotlights

UMC100.3 Universal Motor Controller

The UMC100.3 universal motor controller is future-ready and equipped for advanced motor control tasks. With exceptional usability, unmatched communication, and simple configuration, operation is easier than ever.

ABB's intelligent motor controllers protect and control motors, enable communication via fieldbus and Ethernet, and diagnose faults. Their functionality provides continuous, detailed operational, diagnostic, and service data – an effective source for modern predictive maintenance systems in any plant.

Benefits:

• Reduced wiring effort: saving time, space, and costs.
• Reduced downtime thanks to quick replacement.
• Time savings on technical start-up.
• Seamless integration with the ABB Ability™ System 800xA platform.
• Variety of communication interfaces.
• Safe motor shutdown.

Characteristics:

• Max. motor voltage 1000 V AC.
• Suitable for single-phase and three-phase motors.
• Rated motor current from 0.24 to 63 A, without accessories.
• Up to 850 A with additional current transformers CT4L and CT5L.
• Trip classes 5, 10, 20, 30, and 40 according to EN/IEC 60947-4-1.
• Easy adaptation of communication interfaces inside and outside drawers.
• Standard connections and fieldbus wiring.

CM-MSS Thermistor Motor Protection Relays

CM-MSS series thermistor motor protection relays monitor the winding temperature of motors equipped with PTC temperature sensors. These sensors are embedded in the motor windings, directly monitoring the heat generated by the motor. This direct temperature measurement allows thermistor motor protection relays to assess various motor states, such as overheating, overload, or insufficient cooling. A version with ATEX approval is also available for hazardous areas.

Benefits:

• Easy to use, distinguishing between different operating states and faults.
• Application status check via reading front LEDs.
• Fast and reliable wiring connection thanks to the push-in variant of the CM-MSS series.
• Simpler installation due to completely tool-free mounting and dismounting.
• Adjustment via front DIP switches covered by a label.

Characteristics:

• Approved according to local and international standards for many applications, including renewable energy and marine sectors.
• Dynamic detection of short circuits and open circuits.
• Wide control supply voltage range: from 24 to 240 V AC/DC.
• Reset of faults stored in non-volatile memory, remote reset.
• Multiple international approvals and markings ensure the best quality and conformity with the latest version of product standard DIN EN 60947-8:2013-07 and IEC/EN 60947-8.

MS132 | MS165 Motor Protection Circuit Breakers

Motor protection circuit breakers provide electromechanical protection for the main circuit. They are primarily used for manual connection and disconnection of motors and for protecting them against short circuits, overloads, and phase loss without the need for fuses. Fuse-less protection reduces costs and saves space. It also ensures a fast reaction to short circuits – the motor is switched off in milliseconds. Starters are configured with contactors.

Benefits:

• Harmonized range of basic accessories (auxiliary contacts, signal contacts, voltage releases, undervoltage releases) for the MS1xx and MO1xx product families.
• Compact design.
• Efficient construction and easy mounting, typical for ABB contactors.
• Easy-to-mount busbars allow quick electrical and mechanical connection of several motor protection circuit breakers, forming direct starter sets.
• Shorter downtimes due to motor protection and reduced troubleshooting time.

Characteristics:

• Manual control / protection against short-circuit current and overload.
• Adjustable settings for overload protection and magnetic trip indication.
• Disconnect function.
• Remote control via undervoltage or voltage release.
• Ability to interrupt operation in case of short circuit up to 100 kA.
• Phase loss detection.
• MS132 from 0.1 to 32 A.
• MS165 from 10 to 80 A.

TF and EF Thermal and Electronic Overload Relays

Overload relays provide reliable motor protection against overload or phase loss. Thermal overload relays are economical electromechanical main circuit protections. Electronic overload relays provide reliable and precise motor protection. Both types of relays, along with contactors, can form a compact starter set.

Benefits:

• Reliable motor protection.
• Easy mounting of starter sets.
• Optimized matching with ABB contactors.
• Electronic overload relays reduce logistics costs and improve design with three trip classes in one device.
• In some applications, single mounting kits can be used, and wiring can be rearranged to install remote control.

Characteristics:

• Thermal overload relays TF with trip class 10.
• Electronic overload relays EF with selectable trip class (10E, 20E, 30E).
• Rated motor current: from 0.1 A to 1250 A.
• Adjustable current setting ranges.
• Overload protection with phase loss detection.
• Automatic or manual reset and possibility of sealing.

Compact Soft Starters

ABB's compact soft starter sets offer more functions in less space. The compact unit is only 22.5 mm wide and suitable for three-phase motors up to 3 kW - 400 V AC. These starters feature integrated functions for line power supply, reverse starting, overload protection, and emergency stop. This product range is ideal for long-term, frequent, and reliable switching of machinery such as paper machines, conveyors, pumps, compressors, and machine tools.

Benefits:

• Line power supply, reverse starting, class 10A overload protection, and emergency stop functions in one device.
• Multi-functional product with a width of only 22.5 mm.
• Suitable for single and group mounting.
• Electrical durability: 30 million operating cycles.
• Switching frequency: 2 Hz.

Characteristics:

• Motor control up to 3 kW, 400 V AC and 9 A for resistive loads.
• When combined with ABB's Sentry Safety Relay SSR10, it ensures the highest safety standard SIL 3 and PL e certification.
• Short-circuit protection with ABB's MO132 for single and group mounting of the compact soft starter.
• 24 V DC PLC controller.

CP-C.1 Power Supplies

CP-C.1 power supplies stand out among ABB's offerings with high performance and the highest level of technological advancement. Thanks to excellent efficiency, high reliability, and innovative functions, such a power supply is suitable for the most demanding industrial applications. The power supplies have a built-in power reserve of 50% and operate with an efficiency of up to 94%. They are equipped with overheat protection and active power factor correction. With a wide range of AC and DC input voltages and global usage approvals, CP-C.1 power supplies are the preferred solution for professional DC applications.

Benefits:

• Power reserve and switching of high peak currents allow critical equipment to remain operational.
• High efficiency, reaching up to 94%, reduces energy consumption, leading to financial savings and better space utilization without the risk of component overheating.
• Reliable operation in the harshest conditions due to high resistance to extreme ambient temperatures.
• A PCBA coated version is available for hazardous locations.
• An additional reserve module, CP-C.1-A-RU, provides true redundancy.

Characteristics:

• Rated output voltage 24 V DC.
• Rated output current 5 A, 10 A, 20 A.
• Rated output power 120 W, 240 W, 480 W.
• High efficiency - up to 94%.
• Free convection cooling (no forced fan cooling).

More Information

ABB Contact Center
Tel.: +48 22 22 37 777
Email: kontakt@pl.abb.com

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