Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
No volt coil of DOL starter also known as
Start relay
Stop Relay
Hold On relay
Any of above
Hold On relay
The 'No Volt Coil' (NVC) in a Direct-On-Line (DOL) starter is an electromagnetic coil that keeps the contactor energized when the motor is running. It is referred to as a 'Hold On' relay because its primary function is to hold the main contacts in the closed position once the start button is released.
The 'No Volt Coil' (NVC) in a Direct-On-Line (DOL) starter is an electromagnetic coil that keeps the contactor energized when the motor is running. It is referred to as a 'Hold On' relay because its primary function is to hold the main contacts in the closed position once the start button is released.
Fmag=2g2N2I2μ0A — represents the electromagnetic force exerted by the coil where N is turns, I is current, and g is the air gap.
P=V⋅I — represents the power consumed by the control circuit holding the coil.
When the 'Start' button is pressed, the NVC is energized through the auxiliary contact or the start circuit, creating a magnetic field that pulls the armature to close the main contacts. Once the magnetic circuit is closed, the 'Hold On' auxiliary contact maintains the supply to the coil, allowing the motor to continue running. If the supply voltage drops significantly or fails, the electromagnetic pull diminishes, and a spring releases the contacts to disconnect the motor, providing undervoltage protection.
Provides essential under-voltage or no-volt protection to prevent unexpected motor restart.
Ensures the motor remains disconnected after a power failure until the operator manually presses the Start button again.
Acts as an interlock mechanism in the control circuit logic.
The coil is designed to operate within a specific voltage range, typically 85% to 110% of rated supply.
Automatic motor isolation upon power failure
Enhanced operator safety by preventing automatic restarts
Coil can burn out if voltage is consistently too high
Susceptible to chatter if supply voltage is unstable or dips slightly
Industrial motor control centers
Machine tool control panels
HVAC system starters
The NVC is often connected in series with the Stop button and thermal overload trip contacts to ensure the motor stops under all fault conditions.
Option A (Start relay) and B (Stop relay) are functional descriptors but 'Hold On relay' captures the specific self-latching principle.
C is correct — The No Volt Coil is known as the 'Hold On' relay because it maintains the electromagnetic force necessary to hold the starter contactor in the closed position during normal operation.
In competitive exams, always remember that NVC is for safety; it ensures that the motor does not restart automatically when power is restored, preventing potential accidents.