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The Different DC/AC Motor Starters and Their Applications, Advantages, and Flaws

The motor starters are primarily used for reducing the current or voltage at the time the motor starts initially, and are not used in the self-starting motors. Because abnormally high or very low voltage can damage the components of a motor, the use of motor starters is necessary. Starters also keep the starting speed of the motor constant and avoid problems including short circuit and overloading. In lieu of the circumstances, other components like a circuit breaker or a contractor may also be used along with a starter. In accordance with the types of current viz. AC and DC), starters may also be of two types, viz. DC motor starters and AC motor starters.

DC Motor Starters

The DC motor starters are used for starting and stopping the DC motor safely. They are cheaper when compared to the AC motor starters and also have a simpler construction and built.

When the motor is turned “off”, the armature winding is devoid of any back EMF. The armature winding has a very low resistance. Therefore, when a high or full supply voltage is provided to the motor during its starting phase, a large current amount flows through the winding. This high amount of current may burn the winding or damage components (for instance brushes). If there is a large voltage fluctuation within the voltage main supply, the equipment can be damaged. All these issues are resolved through the use of the DC motor starters. The 3 main varieties of the DC motor starters, along with their benefits and flaws are given below.

2 Point Starters- The starters are used with DC series motors. They find application in cranes and in the railways where they can be used to stop the rail. 2 point starter does not allow the motor to draw high current during starting. It protects the motor in incidences including single phasing, no voltage, over voltage and under voltage.

3 Point Starters- The 3 point motor starters are used typically in the DC shunt motors. They are commonly used in areas including spinning mills and the lathe factories. The 3 point starters offer a number of advantages. They protect the motor from the current surges and in the instances of short circuit fault or overload. We can also use other equipment along with the starter so that it can control the speed of the motor as well. The only disadvantage associated with starters is that they are not useful when combined with the variable speed motor.

4 Point Starters - The 4 point starters are commonly used with the DC compound motor. They can also be used with the DC shunt motors. These starters are commonly used in the rolling mills and the process industries. When you have to protect the variable speed motors, the four-point starters are the best option.

AC Motor Starters

The induction and the AC Motors require the AC starter so that they can start safely. Adverse conditions such as power surges, overload, under load, and circuit failures do not affect the motor adversely when AC starters are used.

When an induction motor is connected directly to the large voltage supply, EMF of high-value effects induction motor’s rotor. Because of the exceptionally large EMF, a high current will flow in the rotor winding. For balancing this, a current also makes way through the stator winding. This current may damage the winding itself. A large fluctuation may also occur in the supply voltage, which damages the other components that may be connected to the line. Below is a brief description of the AC motor starter types.

DOL or Direct Online Starter- These starters are used in compressor, conveyor belts, and in the induction motors having a capacity of 7.5 KW. The cheap starters have a simple construction and can protect motor components in cases of short circuit and overload. The drawback of the starter is that it cannot reduce the starting current of the motor, but only acts as an "off/on” switch.

Stator Resistance Starter- The starters can also be used for motors having a rating greater than 7.5 KW. The starter can reduce the starting current and is quite affordable. The drawback is that the starter can also reduce that torque of the motor.

Auto Transformer Starter- These starters are quite easy to control and are energy efficient (no loss due to resistance). The flaw of the autotransformer starter is that it can also reduce the torque of the motor.

You can concert and a leading supplier to know about the best motor starters options and deals available to you. The starters may prevent an accident, reduce electricity consumption, and enhance the longevity of the motor and components.

Related Articles

It is very important to carefully evaluate the hazardous and operational conditions, before actually ordering industrial electrical enclosure and panel. Apart from securing your components, electrical enclosures also impact the security of those in the vicinities and surroundings. Operators, staff/employees, and many other people may be adversely affected when an improper electrical enclosure with an incorrect rating has been installed.


The basic steps for finding out the current electrical enclosure for an operational environment where hazardous gases are always present include:

•Finding out the NEMA environment rating.

•Determining and finding out the NEC (National Electric Code) explosion protection classification.

•Knowing more about the pressurization and purge type.

•Finding out and specifying the electrical enclosure with the right rating.

Remember that customization and modernization are necessary, and there will be no “one size fits all” solution available for electrical enclosures.

NEMA 4 and 4X Enclosures

The NEMA 4 and 4X electrical enclosures for Class 1 and Class 2 hazardous environment should be customized so that they can overcome the hazardous threats. Electrical enclosures with a NEMA rating of 4 are basically watertight. These electrical enclosures can also resist the formation of ice, dust blown weather, cold conditions, and can also resist hose-directed water and splashing. The 4X variety has additional resistance to corrosion. Therefore the 4X enclosure can only be made of aluminum or stainless steel.

The Hazardous locations may have flammable water vapors and gases, combustible gases and vapors, and/or ignitable vapors present in the atmosphere. The National Electric Code (NEC) classifies the hazardous areas into various zones, divisions, and classes. The Class 1 Division 2 areas only have the flammable liquids, gases, and vapors present in an abnormal condition. But the flammable elements are present in Class 1 Division 1 conditions on a regular scale, and at all the times.

While a leading manufacturer of electrical enclosures will provide you an enclosure with the right NEMA rating, the company will not be able to certify enclosure in accordance with the NEC explosion protection criteria. The operation conditions differ and hence proper customization of the enclosure is necessary before its installation.

Containing the Threat of Explosion

For an explosion to occur in a hazardous environment, the 3 important elements that should be present include heat, oxygen, and flammable substance/fuel. To prevent an explosion, the internal explosion can be contained, or one or more than one of the necessary components for the explosion to occur should be removed.

Pressurization and Purging

Pressure can be created within the enclosure (by using clean or some inert air). This will prevent outside air (containing flammable vapors/gases) to reach the inside of the enclosure. A purge control system and a gasket will create an impregnable seal. Such enclosures have the interlock feature through which access can be provided to their interiors. The NFPA (National Fire Protection Association) has the classification of the pressurization systems. They can be Type X, Type Y or Type Z. These systems vary in the kinds of equipment they can store, the features and capabilities they have, and the divisions in which they can be used.

Customization of the Electrical enclosure in Class 1 Division 2 Environment

The Class 1 Div 2 enclosure may use the right materials and components so that it can overcome the effects of temperature, have the right pressure, and prevent the entrance of the flammable gases to the insides. They are created using the matching gaskets, hinges, cutouts, mechanical interlocks, timer mountings and other kinds of components.

You can consult a reputed supplier/manufacturer of electrical enclosures to have the best solution that can well suit the demands of your particular operation and hazard environment.

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