# Why does line current become half when load becomes half of full load in a dc shunt motor?

So, suppose a dc shunt motor is running at full load. I wanted to know what happens to the torque, speed, armature current and line current when the load changes? How are these related mathematically. In my book it is given that " when load becomes half of the full load, line current also becomes half ", but why? What I think is that when we increase the load from no load to full load, torque increases and since torque is proportional to armature current for a dc shunt motor, armature current should also increase. But when we already are working at full load, maximum armature current would be flowing. So when load becomes half, shouldn't the armature current also become half?

• "when load becomes half of the full load, line current also becomes half " and " So when load becomes half, shouldn't the armature current also become half" are the same statement. Commented Apr 15, 2018 at 9:51
• Line current is equal to armature current plus field current. Line current is not equal to armature current Commented Apr 15, 2018 at 10:00
• Generally the field winding carries a much smaller current (in a shunt-wound motor) than the armature, while developing the same voltage. So the statement that total current halves may be approximately correct even if it isn't strictly so. This is in definite contrast to a series-wound motor, where the field winding carries the same current as the armature but a smaller share of the voltage. Commented Apr 15, 2018 at 10:20