AEMT - Association of Electrical and Mechanical Trades

26 July 2022
Motors in Potentially Explosive Atmospheres
Mawdsleys BER, a specialist in the repair, rewind, refurbishment and supply of electric motors, generators and pumps, looks at potentially explosive atmospheres, the safety standards that govern them and the types of motor that can be used to eliminate the risk of an explosion.

Explosion-proof motors, referred to as Ex motors or ATEX motors, are a special type of motor designed to be used in hazardous environments where the risk of an explosion is higher.

Whether it’s high humidity, extreme temperatures or dust in the air, an explosion-proof motor has safety features in line with the ATEX directive to keep the environment safe.

What Is a potentially explosive atmosphere? Under the ATEX (ATmosphere EXplosible) directive, which covers equipment used in potentially explosive atmospheres, a potentially explosive atmosphere exists when “a mixture of air gases, vapours, mists, or dusts combine in a way that can ignite under certain operating conditions”.

With electric motors, the most common causes of explosion are the surface becoming so hot during operation that it causes ignition or a single arc from a motor malfunction causing ignition.

For this reason, equipment such as motors used in these atmospheres must be specially designed so that they will not cause the atmosphere to ignite, with protections against environmental hazards such as dust, fire and moisture.

Examples of these potentially dangerous environments include fixed offshore platforms, mines, flour mills, wastewater processing plants, workshops that use spray paint and food production lines.

SAFETY STANDARDS

There are two European Directives for controlling explosive atmospheres, which are known as ATEX. ATEX is implemented in the UK through DSEAR, the Dangerous Substances and Explosive Atmospheres Regulations, 2002. The two directives are:

Directive 99/92/EC – also known as ATEX 137 or the ATEX Workplace Directive – imposes the minimum requirements for improving health and safety for workers who may be at risk from explosive atmospheres.

Directive 14/34/EU – also known as ATEX 95 or the ATEX Equipment Directive, concerns the standards of equipment and protective systems that will be used in potentially explosive atmospheres.

An ATEX certification is required to work safely on explosion-proof motors. At Mawdsleys, all of our specialist engineers are ATEX certified and can work on all types of Ex motor.

TYPES OF EXPLOSION-PROOF MOTOR

There are several types of explosionproof motor for use in different environments. The most common types of protection offered by Ex motors are:

Dust ignition proof (Ex t): dust entering a motor can cause damage and potentially ignite. Dust ignition-proof motors have a high ingress protection rating, meaning they can prevent any dust from entering the motor.

Flameproof (Ex d): a spark or flame from a motor can result in an explosion in hazardous environments. Flameproof motors have flame paths built into their shaft and inner bearing covers, joints with long spigots to prevent the flames from escaping and they are encased with a motor housing developed to withstand internal explosions.

Increased safety (Ex ec & Ex eb): previously called ‘non-sparking’ motors, these motors do not spark during normal operation or on start up. There are also no hot surfaces within the motor during running or starting.

The most suitable motor for your operation will be dependent on the hazards present within the environment and the job the motor is required to perform.

INGRESS PROTECTION (IP) RATINGS

A fundamental property of Ex motors that makes them suitable in potentially explosive atmospheres is that they can protect against moisture and solid foreign objects.

If dust, water, or a larger foreign object enters a motor, it can cause damage, motor failure or even a spark or flame that could result in an explosion.

The degree of protection offered by Ex motors is shown by the IP rating, which will be found on the motor nameplate. The IP rating is made of two digits showing how well the motor is protected against solid foreign objects and water, respectively. The first number in an IP rating runs from 0, no protection, to 6, dust tight. The second number runs from 0, no protection, to 9, protection against high-pressure and temperature water jets. In our case, a rating of IP55 would therefore represent a motor which is dust protected and protected against water jets. 

www.mawdsleysber.co.uk

In this story: MAWDSLEYS BER LIMITED
Unit C2 Kingsland Trading Estate, St Philips Road, Bristol, BS2 0JZ
+44 (0)11 7955 2481
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