Direct-on-line starter | DOL starter selection tool

The direct-on-line starter is the cheapest motor starting method. In this method, full voltage is applied to the motor terminals. Here a comprehensive DOL starter selection tool, which can help you calculate the appropriate rating of the contactor, fuse, circuit breaker, and overload relay used in a DOL starter circuit.

Motor data input

Motor Type
Enter the motor rated voltageV
Enter the motor rated power
Enter the motor Efficiency95%
Enter the motor Power factor0.85

Calculated Values

Motor FLCA
Motor Starting CurrentA


DOL Stater rating

Required fuse rating
Required Thermal Circuit Breaker rating
Minimum contactor current rating
Overload Setting

Parts of a DOL starter

This calculator can help you determine the rating of all power circuit components of a DOL starter. An DOL starter consists of the following parts.

  • Circuit breaker or fuse (Sometimes both) – for short circuit protection.
  • Overload relay – for overload protection.
  • Contactor – for switching.

Learn in detail:

How to use the DOL starter selection tool?

The above tool requires following data for calculation:

  1. Motor Type – Single-phase or three-phase. (Mandatory)
  2. Motor rated power in HP or kW. (Mandatory)
  3. Input supply voltage. (Mandatory)
  4. Motor Efficiency as per nameplate – (if known).
  5. Rated power factor (if known).
DOL name plate motor

After entering the required data, click on the “Calculate” button to find out the required fuse rating, Circuit Breaker rating, contactor current rating, and overload setting.

DOL starter circuits

DOL selection tool

Read more: How to calculate ratings of contactor and overload

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