Page 105 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

D.O.L. starter

Objectives: At the end of this lesson you shall be able to:
• state the specification of a D.O.L. starter, explain its construction, operation and application
• explain the necessity of a back-up fuse and its rating according to the motor rating.

A D.O.L. starter is one in which a contactor with no-volt relay, ON and OFF buttons, and overload relay are
incorporated in an enclosure.
Construction and operation: A push-button type, direct on-line starter, which is in common use, is shown in

Fig 1. It is a simple starter which is inexpensive and easy to install and maintain.
There is no difference between the complete contactor circuit explained in Exercise 2.3.125 and the D.O.L.
starter, except that the D.O.L. starter is enclosed in a metal or PVC case, and in most cases, the no-volt coil is
rated for 415V and is to be connected across two phases as shown in Fig 1. Further the overload relay can be
situated between ICTP switch and contactor or between the contactor and motor as shown in Fig 1, depending
upon the starter design. Trainees are advised to write the working of the D.O.L. starter on their own
Specification of D.O.L. starters: While giving specification, the following data are to be given.
D.O.L. starter
Phases - single or three.
Voltage 240 or 415V.

Current rating 10, 16, 32, 40, 63, 125 or 300 amps.
No-volt coil voltage rating AC or DC 12, 24, 36, 48, 110, 230/250, 360, 380 or 400/440 volts.
Number of main contacts 2, 3 or 4 which are normally open.
Number of auxiliary contacts 2 or 3. 1 NC + 1 NO or 2 NC + 1 NO respectively.

Push-button - one `ON’ and one `OFF’ buttons.
Overload from setting – amp-to-amp. Enclosure - metal sheet or PVC.
Applications: In an induction motor with a
D.O.L. starter, the starting current will be about
6 to 7 times the full load current. As such, D.O.L.
starters are recommended to be used only up to 3
HP squirrel cage induction motors, and up to 1.5
kW double cage rotor motors.
Example

A 3-phase, 400V, 50 HZ, delta-connected
induction motor draws a line current of 150 amps
with a P.F. of 0.85 and is delivering an output of
100 (Metric) HP. Calculate the efficiency.
% of efficiency = Output x 100
Input

100 x 735.5 x 100
=
3 x 400 x 150 x 0.85

= 83.3 %

92

CITS : Power - Electrician & Wireman - Lesson 70-75 CITS : Power - Electrician & Wireman - Lesson 70-75