The electric motor is one of the most revolutionary inventions in recent history and has drastically changed the framework of human society. Today, electric motors are used in countless everyday objects, from appliances such as fans, refrigerators, and vacuum cleaners to vehicles, conveyor belts, and power tools.
Modern industries have become so reliant on electric motors, and it is estimated that approximately 45% of the global power usage is directed towards running electric motors in various applications. By comparison, lighting accounts for only 19% of the total global energy consumption.
This guide will explain exactly how electric motors work and describe the different types in use across industries.
What is an Electric Motor?
An electric motor is a device that converts electrical energy into mechanical energy. Put simply, motors use electricity to produce a specific motion (usually rotational). There are several types of electric motors. However, they all work based on the principle of electromagnetism. Almost all motors consist of a combination of some or all of the following essential elements:
An armature or rotor
The armature interacts with a magnetic field generated by a stator in the presence of current generated by an AC or DC power source to develop a mechanical torque in the axle or shaft. These elements can vary depending on the type of motor used. Some of the most common motor types include:
AC brushless motors
DC brushed motors
DC brushless motors
These motors vary in the way the conductors and the magnetic field are arranged and the input power source is used to produce the resulting motion. Other types of motors are also available; each having slightly different configurations for better suitability in different applications.
Types of Electric Motors
DC motors are electric motors driven by a DC power source. These motors are available in two main variations: brushed and brushless.
In brushed DC motors, small carbon-based conductors, called brushes, are used to deliver charge to the commutator rings which cause the armature to rotate due to its interaction with a magnetic field. The rotation of the armature can be easily reversed by altering the polarity of the brushes. Brushed DC motors are more cost-effective and less complicated than other motors. Typical uses of brushed motors include alternators, generators, and some kitchen appliances.
In DC brushless motors, embedded electric controllers and sensors are used to alternately charge stator coils to attract and rotate a series of electromagnets. These motors were developed to occupy less space and achieve higher performance than brushed DC motors. These motors are also referred to as BLDC motors. The brushless design eliminates the possibility of brush wear, making these motors suitable for applications that require durability such as electric vehicles, cordless tools, HVAC equipment, and positioning control systems.
AC Motors are driven by an AC power source. The two primary variations of AC motors are synchronous or asynchronous (induction) motors.
Synchronous AC motors are highly precise motors that can run at a constant speed regardless of the load acting on them. The main operation of the motor is achieved by the interaction between a steady magnetic field (produced by the windings on the rotor) and a rotating magnetic field (produced by the stator); this results in overall rotational movement of the rotor. Synchronous AC motors are used in applications where accuracy is critical such as clocks, timers, robotics, metering pumps, and speed controllers.
AC brushless motors use the principle of electromagnetic induction to produce a magnetic field generated by the stator. The alternating current in the stator creates a constantly revolving electromagnetic field or a rotating magnetic field (RMF). The relative speed between the RMF and the rotor will cause a current to be induced in the rotor’s conductors, generating an electromagnetic force in accordance with Lorentz’s force law. Induction motors are one of the most common types of electric motors used today. They are used across a broad range of applications including fans, water pumps, automobiles, air conditioners, and kitchen appliances.
Other types of motors may fall under the general classification of AC and DC motors, including:
Servo motors – These use feedback sensors to facilitate the positioning of components such as actuators and robotic arms.
Stepper motor – Stepper motors use external electromagnets to electronically control an internal rotor. Differently positioned stators divide the full rotation into an equal number of steps. Stepper motors are known for their precise positioning, making them ideal for applications such as robotics, hard disk drives, and telescopes.
Universal motors – These general purpose motors are designed to work with either DC or single phase AC power supplies. They are commonly used in railway traction mechanisms, power tools, and household appliances.
Hazardous Location Motors
Hazardous location motors are motors that are designed for safe operation in environments that contain gas, vapor, or dust that is potentially explosive or ignitable. These motors must be able to safely contain any ignitions or explosions within their housing without igniting the surrounding air.
To ensure that motors are suitable for operation in hazardous environments, they must comply with specific classes, divisions, and group classifications outlined in standards and specifications stipulated by the NFPA 70® – National Electrical Code® (NEC), and the Canadian Electrical Code (CEC).
Every motor carries a label that identifies its suitability for operating in different hazardous environments. Class I covers ignitable gases, vapors, and liquids, Class II covers electrically conductive and potentially explosive dust, and Class III covers ignitable fibers or lint, such as saw dust or textiles.
Electric Motor Services by Dietz Electric
At Dietz Electric, we offer a range of custom electric motors, drives, and power transmission systems from a variety of leading manufacturers. We draw on over four decades of experience to supply motors for many applications in any operating environment. We also specialize in modifying and repairing electric motors.
Hazardous area classification systems identify electrical equipment locations with potential fire and explosion risks and establish the necessary protections and installation methods based on the type, properties, and severity of the hazard. Companies in the USA and Canada use two classification systems: traditionally, the Class/Division/Group system and, increasingly, the Zone system employed throughout the rest of the world.
The Class/Division/Group system uses three designators to categorize hazardous areas:
Class:The Class designator defines the general nature of the hazard, such as its state of matter or form.
Division:The Division designator indicates the probability of a hazard igniting or producing an explosion.
Group:The Group designator describes the type of hazard with greater specificity than the Class designator and identifies precise chemical and material compositions within the surrounding atmosphere.
Hazardous area classifications significantly impact the operations of the power generation industry. However, every industry that uses electrical equipment needs to be aware of the risk of ignition or explosion. Products and components can that be affected by hazardous area classification systems include:
Combustion-based electrical generator plants
Electrical equipment with hot surfaces
Fuel and ignition systems
Generator cooling systems
Recognized approval agencies ensure a facility’s electrical equipment is designed, constructed, and installed according to the country’s established laws, regulations, and codes.
National Electrical Code (NEC) Article 500 and National Fire Protection Agency (NFPA) 497 establish the Class/Division/Group system for classifying hazardous areas. This system allows for precise, standardized communication about the types of hazardous locations by classifying them based on the type of material (Class), the probability of explosion or ignition (Division), and the products comprising the hazards (Group).
Each class describes the nature of the hazardous compound. This qualification is important because different material types react to the presence of heat and electricity differently.
Class I: Gases or vapors.Class I hazardous areas may contain flammable vapors or gases in quantities large enough to cause a fire or an explosion. Examples of these gases and vapors include hydrogen, carbon monoxide, and ethylene oxide.
Class II: Dust.Class II hazardous areas may contain combustible or conductive dust in quantities large enough to cause a fire or an explosion. Examples of these dusts include metal dusts such as aluminum dust or carbon-based dusts such as coal dust.
Class III: Fibers and flyings.Class III hazardous areas may contain fibers and flyings (i.e., small airborne parts) in quantities large enough to ignite and cause a fire or an explosion. Examples of these fibers and flyings include wood, plastic, and grain.
Hazardous areas don’t always maintain a constant level of risk. In these circumstances, rather than evaluating these areas along a spectrum or constantly reevaluating at-risk areas, facilities classify them by their likelihood of having hazardous materials.
Division 1: High probability. Division 1 areas are highly likely to experience a fire or explosion under ordinary operating conditions. Packaging areas within food processing plants that routinely have airborne starch are an example of Division 1 areas.
Division 2: Low probability. Division 2 areas are highly unlikely to experience a fire or explosion during typical operations. However, under abnormal operating conditions, fire or explosion may still occur. An example of a Division 2 area is closed-loop fluid heating systems that use hot oil as the oil is only present outside of the system during equipment malfunctions.
The seven group designators define the specific type of hazardous compound more precisely than class designations:
Group A:Contains acetylene.
Group B:Contains flammable gases, flammable liquid-produced vapors, or aerosolized combustible liquid-produced vapors, in which the Minimum Igniting Current (MIC) ratio <0.40 or the Maximum Experimental Safe Gap (MESG) is <0.45 mm. Examples of Group B contents include acrolein, butadiene, hydrogen, or propylene oxide.
Group C:Similar contents to Group B but with a MIC ratio of 0.40<MIC≤0.80 or a MESG of 0.45 mm<MESG≤0.75 mm. Examples of Group C contents include carbon monoxide, cyclopropane, ether, or ethylene.
Group D:Similar to Group B and C conditions but with a MIC ratio >0.80 or a MESG >0.75 mm. Examples of Group D contents include acetone, ammonia, benzene, butane, and gasoline.
Group E:Contains combustible metal dusts, such as aluminum alloy, bronze, chromium, titanium, and zinc.
Group F:Contains combustible carbon-based dusts with ≥8% volatile compounds, such as coal and coke.
Group G:Contains solid dusts, fibers, or flyings not covered by the Groups E or F, such as flour, starch, sugar, wood, and plastic particles.
Under this comprehensive system, hazardous areas are classified as Class [X], Division [Y], Group [Z]. For example, a mine with aluminum dust frequently present is designated as Class II, Division 1, Group E.
While the USA and Canada widely employ the Class/Division/Group classification system, the rest of the world uses the Zone classification system. Based on National Electrical Code (NEC) Articles 505 and 506, this system also uses Zones/Groups method as established by the International Electrotechnical Commission (IEC).
Zones describe the general nature of the compound and the probability of its concentration causing an explosion or igniting. There are six zones: three for gases, vapors, and mists as described under NEC Article 505 and three for dusts as defined under NEC Article 506. The zones are:
For Gases, Vapors, and Mists:
Zone 0:Continuous or near-continuous presence of ignitable or combustible concentrations of gases and vapors during typical operations.
Zone 1:Highly likely that ignitable or combustible concentrations of gases and vapors are present during typical operations.
Zone 2:Unlikely that gases and vapors will be present in ignitable or combustible concentrations during typical operations or the levels may only be present for short durations.
Zone 20: Continuous or near-continuous presence of combustible dusts or ignitable fibers and flyings during typical operations.
Zone 21:Highly likely that combustible or ignitable concentrations of dust or fibers and flyings are present during typical operations.
Zone 22:Unlike that combustible dusts or ignitable fibers and flyings will be present in high enough concentrations during typical operations or may only be present for short durations.
Similar to the Group designator in the Class/Division/Group system, groups in the Zone system describe the type of airborne material with more detail. These designations also specify information about the site of the hazardous area. The groups include:
Group I: Mines.Mines are susceptible to naturally occurring flammable gas mixtures—i.e., firedamps.
Group II: Explosive Gas.Group II areas are non-mine areas that are prone to the occurrence of firedamps. These atmospheres contain gases such as petrol and methane (Group IIA), ethylene and ethyl ether (Group IIB), and hydrogen or carbon disulfide (Group IIC).
Group III: Explosive Dusts.These atmospheres contain non-gaseous hazards such as combustible dusts and ignitable fibers or flyings. Examples of these compounds include combustible flyings (Group IIIA), non-conductive dusts with high electrical resistivity such as cement dust (Group IIIB), and conductive dusts such as aluminum dust (Group IIIC).
Under the Zone system, areas are designated in the following format: Zone [X], Group [Y]. For example, the same mine with continuous aluminum dust is designated as Zone 20, Group IIIC.
Who Certifies Equipment Used in Hazardous Areas
Government or independent approval agencies certify electrical equipment intended for use in various hazardous locations. In North America, three of the principal agencies are:
Underwriters Laboratories (UL)
Underwriters Laboratories (UL) provides certification, evaluation, and testing services. They certify products based on their adherence to both ordinary location safety measures and hazardous area protection methods. UL also requires compliance with ANSI and CAN standards.
Every division marking has an area classification under the Class/Division/Group system and includes the product’s temperature class. UL certified products are marked as UL listed or UL classified.
Factory Mutual (FM)
Factory Mutual (FM) has a global certification program. In addition to certifying equipment for use in hazardous locations, the agency tests and evaluates building materials, roofing and wall assemblies, and construction, electrical, and fire-related detection equipment.
“FM Approved” certifications mark the specific model of approved equipment and the FM approval class.
Canadian Standard Association (CSA)
Canadian Standard Association (CSA) provides testing, inspection, and certification services. The organization employs either the Class/Division/Group system or the Zone system when marking certified equipment and products. CSA marks may also include the temperature class, protection concept code, and gas group as needed.
Contact Dietz Electric Today
At Dietz Electric Co., Inc., we specialize in supplying and servicing motors designed for use in hazardous areas. Our engineers have years of experience with motors that are UL, FM, and CSA certified.