General Requirement For Motor Starter

When we plan to install new motor starter,we need to consider a few requirement that we want to apply to get a best design,tidy and easy to troubleshooting if have any problem.

Normally motor starter component includes a drive (VFD),electrical wiring,control panel,communication system (Ethernet / Devicenet) and types of starter that we plan to use.

From the design stage,we must follow general requirement for Motor starter to get a best result for our installation.Below I listed some of requirement to build a motor starter.I hope it’s can give a clear view or guide line during design a motor starter.


1) Due to the varying power throughout the world, drives are required for all motors on equipment designed for global use.

2) If the Human Interface Module is mounted in the door of an enclosure it must retain the enclosures design integrity. If not, H.I.M. shall be mounted on the Variable Frequency Drive (VFD).

3) All Variable Frequency Drives shall be equipped with thermal motor overload, ground fault trip and remote alarm (dry contact). The following items are configurable: variable torque, constant torque, constant horsepower, acceleration/deceleration profiles, and current limiting.

The base installation for all VFDs shall be open loop unless better than 3% accuracy is required on speed control, or if the torque demand is extensive at low speeds, in which case either closed loop or open loop vector control shall be considered.


1) Where Variable Frequency Drives or Servo Drives have the capability to have a separate control power feed and motion bus power feed, it shall be utilized.

2) Variable Frequency Drives are required to be rated to operate to manufacturer’s specification with machine/ process skid design voltage applied. The designed frequency range shall not extend outside the boundaries of 10 – 90Hz for all required functions of the equipment.

3) Overload relay shall be mounted in the drive enclosure, where possible. If this is not possible then the relay shall be mounted in an external enclosure adjacent to the drive. The overload relay shall be installed such that it can be reset without exposing personnel to any live circuits.

4) Line reactors shall be based on manufacturer’s recommendations. At a minimum, they are required on the load side for all drive applications where the wire length is greater than 50 feet.


1) In an effort to minimize design and installation costs, using communication networks to communicate between logic controllers and drives is recommended. All non-critical control signals to the drive or motion controller should be sent over this network thus reducing the amount of wiring to the controller.

2) OEM must obtain permission from the PC&IS Control Contact on how variable frequency drives will communicate with the control system.

3) Local implementations of DeviceNet / Ethernet are preferred; Profibus is acceptable but not recommended and requires the approval of the Electrical Engineer.

Control panel



1) Refer to the manufacturer’s installation manual for recommended clearances around the drive controller to provide adequate airflow for cooling.

2) Follow manufacturer’s recommendations for all cable lengths.

3) Motor cables should be shielded and connected to both the drive frame and the motor frame.

4) No more than 3 sets of motor leads from drive controllers should be routed through the same single conduit.

5) Control cables shall not pass the variable frequency drive within .3m (12in). Control cables shall not parallel motor power cables.

6) All feedback (encoder, resolver) wiring shall also be routed away from power cables. Wireway with a divider may be used.

7) Disconnects for VFDs can be located on either the line or load side of the VFD depending on local codes. If the disconnect is mounted on the load side of the VFD it must be capable of disabling the VFD prior to opening the contacts. To achieve this requirement it is recommended that two normally open auxiliary contacts be wired to the VFD enable circuit where applicable to disable the output prior to opening the motor lead contacts.

8) Suppression devices shall be installed on all relays; solenoids and brake coils located in close proximity (same control panel) of the VFD to reduce electrical noise.

9) Most VFDs do not provide short circuit protection on the input power; therefore it is a recommendation that a fuse block be installed on the line side of the VFD to protect against short circuits. Fuses must be capable of interrupting the maximum short circuit current available from the power source.(refer to the VFD manufacture for the recommended fuse sizes)


1) All AC motor starters are to be full voltage, 1 phase or 3 phase, 50/60 Hz, with manual overload reset button in the cover, externally operated with an auxiliary contact.

2) Starter coils shall have 24VDC control. An interposing relay (with a 24 VDC coil) may be required for larger starter sizes.

3) Circuit breakers in combination starters must be “horsepower rated”, i.e., the breaker must be capable of interrupting the current under locked rotor conditions.


  1. Niraj Raval says

    Sir i need help how can we connect as well as what capacity capacitor we can connection to and individual 3phase , 415 v AC,50 Hz squirrel cage and induction motor to improve power factor.
    please suggest some guide lines or formula for my request.

  2. Niraj Raval says

    Sir i need help capacitor connnection and it’s value selection for 3 phase , 415 v AC , squirrel cage and induction motors connection individually to inprove power factor .

  3. Hi!,I want to know how can I use 2 wire to make star Delta starter?

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