4 Point Starter in DC Motors: Construction, Working, Advantages, Disadvantages, Applications & SSC JE MCQs

1. Introduction

The 4 Point Starter is an improved version of the 3 Point Starter designed to start and protect DC shunt motors. It is widely used because it eliminates the disadvantages of the 3 Point Starter and provides better protection.

2. Construction of 4 Point Starter

The 4 Point Starter consists of the following parts:

Main Terminal (T): Connected to supply.
Armature Terminal (A): Connected to motor armature.
Field Terminal (F): Connected to shunt field winding.
Starting Resistance (R): Series resistors for controlling starting current.
Starting Handle (S): Movable lever that moves over studs controlling resistance.
No-Volt Release Coil (NVR coil): Connected separately to supply and field circuit to hold the handle.
Overload Release Coil (OLR coil): Connected in series with armature for overload protection.
Fourth Point: Separate supply terminal for NVR coil, independent of field circuit.

Note: Unlike 3 Point Starter, the NVR coil in 4 Point Starter is connected independently from the field circuit, providing better protection.

3. Working Principle of 4 Point Starter

In the 4 Point Starter, the NVR coil is connected directly to the supply line instead of the field winding circuit. This removes the problem faced in the 3 Point Starter where NVR coil loses voltage if the field circuit is broken.

When the motor is started, the handle is moved from 'off' towards 'run' position gradually cutting out starting resistance and increasing armature voltage.

The OLR coil connected in series with the armature provides overload protection by tripping the starter if current exceeds safe limits.

If the supply voltage fails, the NVR coil de-energizes and the starter handle returns to the off position, stopping the motor.

4. Advantages of 4 Point Starter

Does not depend on the field circuit for no-voltage protection.
Provides better and reliable overload and no-voltage protection compared to 3 Point Starter.
Eliminates the risk of the motor running with a broken field circuit.
Simple to operate and economical.

5. Disadvantages of 4 Point Starter

Still requires manual operation to start the motor.
Limited to DC shunt motors.
Not suitable for series motors.

6. Applications of 4 Point Starter

Starting DC shunt motors in industrial applications.
Used where improved motor protection is required over 3 Point Starter.
Common in fans, pumps, machine tools, and lathe machines.

7. SSC JE Previous Year MCQs on 4 Point Starter

Q1. What is the main difference between a 3 Point and 4 Point Starter?
a) Number of overload coils
b) NVR coil connection is independent in 4 Point Starter
c) Starting resistance is different
d) 4 Point Starter is only for series motors
Answer: b) NVR coil connection is independent in 4 Point Starter

Q2. Why is the 4 Point Starter preferred over the 3 Point Starter?
a) It is cheaper
b) It provides no-voltage protection even if the field circuit fails
c) It requires no manual operation
d) It can start series motors
Answer: b) It provides no-voltage protection even if the field circuit fails

Q3. In a 4 Point Starter, the overload release coil is connected in series with:
a) Supply
b) Field winding
c) Armature
d) Starting resistance
Answer: c) Armature

Q4. Which type of motor is suitable for a 4 Point Starter?
a) DC series motor
b) DC shunt motor
c) Universal motor
d) Induction motor
Answer: b) DC shunt motor

Q5. What happens if the supply voltage fails in a motor connected with a 4 Point Starter?
a) Motor continues running
b) Starter handle returns to OFF position and motor stops
c) Motor runs at low speed
d) Overload coil trips
Answer: b) Starter handle returns to OFF position and motor stops

8. Conclusion

The 4 Point Starter is an improved and safer version of the 3 Point Starter, providing reliable overload and no-voltage protection to DC shunt motors. It overcomes the disadvantages of 3 Point Starter and is widely used in industrial motor starting applications.

9. FAQs

Q1. Can the 4 Point Starter be used for DC series motors?
No, it is mainly designed for DC shunt motors.

Q2. How does the 4 Point Starter improve no-voltage protection?
By connecting the NVR coil independently from the field circuit, it ensures no-voltage protection even if the field circuit fails.

Q3. Does the 4 Point Starter provide overload protection?
Yes, through the overload release coil connected in series with the armature.

Comparison Between 3 Point Starter and 4 Point Starter

Parameter	3 Point Starter	4 Point Starter
Number of Connections	Three terminals: Armature (A), Field (F), and Supply (T)	Four terminals: Armature (A), Field (F), Supply (T), and Separate terminal for NVR coil
No-Volt Release (NVR) Coil Connection	Connected in series with the field winding	Connected independently to supply, separate from field winding
No-Voltage Protection	Fails if field circuit is broken (NVR coil loses voltage)	Effective even if field circuit is open or broken
Overload Protection	Provided by overload release coil connected in series with armature	Same overload protection via overload release coil in series with armature
Starting Handle Holding	Held by NVR coil in field circuit	Held by NVR coil independent of field circuit
Suitability	Used mainly for DC shunt motors but limited by field circuit dependency	Used for DC shunt motors with improved reliability
Risk of Motor Running with Broken Field	Possible risk if field circuit breaks and starter handle gets stuck	Eliminated due to independent NVR coil connection
Complexity	Simple construction	More complex due to additional terminal and wiring
Cost	Less expensive	Relatively more expensive
Manual Operation	Required	Required