Motor Electrical Protection

INTRODUCTION 

  • Electrical supply, while generally exceptionally reliable, is subject to influences that can result in inadequately protected motors being damaged.
  • As the heart of the motor is the windings, we need to protect the windings from failure.
  • During normal operation, thermal, mechanical and electrical stresses can be encountered by motors. 

POSSIBLE PROBLEMS 

  • Refer to page P-1 in the Fan Trouble Shooting section for a list of possible problems and solutions. 

PROTECTION DEVICES 

  • There are motor protective devices available which detect a range of abnormal conditions and automatically switch off the motor.
  • Different protective devices and the conditions they protect are: -

Fuses

  • - short circuit between phases or earth
  • - high current overload

Thermal Overload Relays

  • current overload
  • start-up problems
  • stalling
  • phase imbalance (three-phase motors)
  • over-temperature
  • phase loss (single-phasing of three-phase motors)
  • under-voltage
  • incorrect phase sequences (three-phase motors)

Thermistors and Thermal Contacts

  • l over-temperature of the windings 

WARRANTY 

Note that warranty is void if the thermal contacts are not used.

  • SABS wiring rules state that motors required to run unattended shall be fitted with over-temperature devices such as thermal overload relays.
  • If this is not complied with, warranty will be void.
  • A licensed electrical contractor or engineer, experienced in motor protection, should be engaged to assess the motors and specific requirements of the installation.
  • An incumbent in possession of a wireman certificate shall do the final electrical connection to the fan.
  • On all motors above 5,5 KW soft starting or star delta starter to be utilized.
 
Download pdf file
 

TDE

The Multiflow TDE 500 to 710 range consist of fully cased, cylindrical models with circular mounting flanges at both ends and a wired terminal box.

RVF

The Mini Centrifugal Roof Fan series are the new type roof extract units available in 2 sizes and suitable for vertical and horizontal installation. The low noise external motor and high efficient backward bladed impeller meets the requirement of efficient ventilation in residential, commercial and light industrial applications.

Future 150

The Decor Series can be wall or ceiling mounted and is designed to exhaust stale and moist air from bathrooms, toilets, laundries etc. They are also suitable for ventilating all types of small or closed areas.

TD Silent

The Silent Series is a low profile mixed-flow in-line fan that produces low noise when in operation. It does this through a specifically designed perforated internal skin that directs sound waves produced inside the fan to a layer of sound absorbent material.

NEW!! TD-EVO

The low-profile TD-EVO 250 and 315 in-line mixed-flow fans for circular ducts have a unique design where the support bracket allows the motor and impeller assembly to be fitted or removed without dismantling the adjacent ducting.

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