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Digital overload relays VS Thermal overload relays

What is an Overload relay?

An overload relay is an electrical device used to turn OFF the motor automatically on overload, i.e if the supplied voltage is higher than the suited value of the motor pump. This is necessary to prevent the burning of coil of the motor.

Why is it important to have an overload relay?

People are under a misconception that it is normal for a water pump coil to be burnt often. Each rewind will cost a hole in the pocket, Approx 7,000 to 10,000 indian rupees.

This can be easily avoided with an overload protection device that trips off the motor when it senses an excessive electrical input. Some more advantages of using an overload relay are :

  • Prevent damage to motor.
  • Prevent loss due to breakdown downtime of water pump.
  • Save yearly maintenance and repair costs.
  • Increase life of the motor pump.

What are the types of overload relays available?

  1. Thermal Overload Relay : An overload relay that works on heating principle ( Thermostat), The motor is tripped off when it reaches a high temperature due to the excess current flow.
  2. Digital Overload Relay : This is an advanced overload relay that works by monitoring the current and voltage of the input and as soon as it reaches a higher than normal value. It trips ofo the motor pump immediately.

Conclusion, Which is better?

Although Thermal overload relays have been used from a long time, It’s technology is outdated.  Thermal overload relays operate on the thermal/ heating principle. The tripping/switching OFF time of thermal overload relays are usually more (close to 1.5 minutes). This again is dependent on the climate. The thermal relays trip faster (1.5 mins) in summers and way slower (upto 3 mins) during winters. If the motor runs on overload for 1.5 minutes, the coils/windings will already be damaged/ weakened . This makes it no point to use the age old thermal overload relays. The digital relays use time based tripping. Naren UCOCR-2 overload relay trip at the same time round the year irrespective of the seasons.

Tripping time for Overload:  12 seconds

Tripping time for Dry run:  8 seconds

Tripping time for Single Phase: <2 seconds

Digital Overload relays are far superior compared to thermal counterparts, Since it’s reaction time is faster and not dependent on the weather.

overload relay for water pump

Advantages of Naren Digital Overload Relay

  • Protection against Overload
  • Protection against Dry Run
  • Protection against Single Phasing
  • Protection against motor cable cut
  • 3 Phase Ammeter
  • 2 Phase Voltmeter
  • Error Display
  • Effective Tripping time
  • Simple to set up
  • 6 months warranty
  • Compatible with all existing 3 Phase motor starters

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