In many industrial and public sectors, explosion protection or explosion hazards are ever-present, e.g. in the chemicals industry, in refineries, on drilling platforms, at petrol stations, in feed manufacturing and in sewage treatment plants.

The risk of explosion is always present when gases, fumes, mist or dust are mixed with oxygen in the air in an explosive ratio close to sources of ignition that are able to release the so-called minimum ignition energy.

In the chemical and petrochemical industries in particular, when crude oil and natural gas are transported, or in mining, milling (e.g. grain and granular solids), this can result in serious injury to persons and damage to equipment.

To ensure maximum safety in these areas, legislators in most countries have implemented appropriate stipulations in the form of laws and regulations based on national and international standards.

Explosion-protected equipment is designed such that an explosion can be prevented when it is used properly.

The explosion-protected equipment can be designed in accordance with various types of protection.

The local conditions must be subdivided into specified zones by the user with the assistance of the responsible authorities in accordance with the frequency of occurrence of an explosion hazard. Device (equipment) categories are assigned to these zones. The zones are then subdivided into possible types of protection and therefore into possible equipment (product) types.

Classification of zones

Areas subject to explosion hazard are divided into zones. Division into zones depends on the chronological and geographical probability of the presence of a hazardous, potentially explosive atmosphere. Information and specifications for classification of the zones are laid down in the following standards:

• IEC/EN 60079?10?1 for gas atmospheres
• IEC/EN 60079?10?2 for dust atmospheres

Further, a distinction is made between various explosion groups as well as temperature classes and these are included in the hazard assessment.

Depending on the particular zone and therefore the associated hazard, operating equipment must comply with defined minimum requirements regarding the type of protection. The different types of protection require corresponding measures to prevent ignition that should be implemented at the motor in order to prevent that a surrounding explosive atmosphere is ignited.

¹⁾ Motors, which are certified for gas or dust protection, must not be used in hybrid mixtures! Hybrid mixtures: When explosive gas and dust atmospheres occur simultaneously.

²⁾ Motors are not approved for operation in environments containing conductive dust.

Types of protection

Type of protection "Non-sparking" Ex nA acc. to IEC/EN 60079-15

The type of protection Ex nA ensures that a motor in normal operation as well as when operated under deviating conditions as specified in the standard is not in a position to ignite a surrounding explosive gas atmosphere.

Type of protection "Dust explosion protection" Ex tc acc. to IEC/EN 60079-31

This type of protection applies for electrical equipment protected using an enclosure and with limited surface temperature for use in areas in which combustible dust can occur in concentration levels that could cause a fire or an explosion.

Explosion-proof motors for converter-fed operation

Principally, explosion-proof motors can be fed from converters. Particular attention must be paid to the interaction between the motor and converter system, especially with regard to the following aspects:

• The harmonic content of the supply voltage raises the motor temperature, so the motor output must be reduced (see derating)
• Less cooling of the motor at speeds below the rated speed
• Voltage stress on the motor winding
• Bearing currents

Certification

IEC motors for use in hazardous zones are certified according to the IEC/EN 60079-0, IEC/EN 60079-15 or IEC/EN 60079-31 standards and EC Directive 94/9/EC (ATEX) and are marked according to the following schematic.

Additional information on the subject of explosion protection, types of protection and zones is provided in the Siemens brochure "Explosion Protection".

Overview of SIMOTICS FD 1MM, 1MH, 1MQ, 1MN explosion-proof motors

SIMOTICS FD explosion-proof motors (1MM, 1MH, 1MQ, 1MN) correspond to the SIMOTICS FD non-explosion-proof motors (1LM, 1LH, 1LQ, 1LN). All technical specifications can be found in the selection and ordering data for the non-Ex motors 1LM, 1LH, 1LQ, 1LN (sections 4 to 7 of the catalog), whereby the rated output is subjected to derating in accordance with defined factors. For derating factors, see "Technical specifications" section "Derating".

To order explosion-proof motors, the letter "L" in position 2 of the Article No. for non-Ex motors must be replaced with the letter "M".

The table below contains a complete overview of our explosion-proof motors, their types of protection and their assignment to categories. It is important to note that depending on whether the motor is used for converter-fed operation or mains-fed operation, different order codes are required for unique selection of the required motor.