What are motor overloads?

What are motor overloads?

Motor overload occurs when a motor is under excessive load. The primary symptoms that accompany a motor overload are excessive current draw, insufficient torque and overheating. Excessive motor heat is a major cause of motor failure.

How does a motor overload work?

When the motor draws excess current, it is referred to as an overload. This may cause overheating of the motor and damage the windings of the motor. This leads to the removal of the power to the motor. Without power, the motor and motor circuit components do not overheat and become damaged.

What should motor overloads be set at?

The overloads are determined using 125% of the FLA, 7A x 1.25 = 8.75A. The maximum allowable size for the overloads is 9.8A. The overloads can be sized at 140% of the FLA if the overloads trip at rated load or will not allow the motor to start, 7A x 1.4 = 9.8A.

What causes a motor to overload?

Electrical overload or over-current is caused by an excessive current flow within the motor windings, exceeding the design current which the motor is able to carry efficiently and safely. This can be caused by a low supply voltage, resulting in the motor drawing in more current in an attempt to maintain its torque.

What are four types of overloads?

A few different types of overload relays include Bimetal Overloads, Ambient-Compensated Overload Relay, and Electronic Overload Relays.

  • Bimetal Overloads use a bimetal strip that acts as a trip lever.
  • Ambient Compensated Overload Relays are similar to Bimetal Overloads.

What are the three types of overload?

There are three types of thermal overload relays — bimetallic, eutectic, and electronic. Bimetallic thermal overload relays (sometimes referred to as heater elements) are made of two metals, with different coefficients of thermal expansion, that are fastened or bonded together.

How do electronic overloads work?

Electronic overload relays do not have a bimetallic strip inside. Instead, it uses temperature sensors or current transformers to sense the amount of current flowing to the motor. Temperature is sensed using PTC and the same is used to trip the circuit in case of overload faults.

How do you check motor overload?

Overload Protection Test:

  1. Measure the normal motor running current (i motor).
  2. Turn off the motor and let it cool for about 10 minutes.
  3. Calculate the following ratio: i (motor) / i (overload min FLA).
  4. Set the overload to its minimum FLA and turn on the motor.
  5. Wait for the overload to trip.

What is the simplest way to determine if a motor is overloaded?

The simplest way to determine if the motor is overloaded is to find the motor full load current on the nameplate and then check the running current with an ammeter.