There is this one particular thing I don't understand. I was going through the text book exercise and found this question.
What happens if the machine being driven by the motor jams, so that the rotor suddenly stops turning?
The book stated that
There would be no Back EMF induced on the coil by the magnets of motor and large amount of the current would pass through the coil which can melt the coil.
I have no problem understanding this. After this, there was written that
When the motor is first turned on, there's a momentary surge of current until the motor picks up speed. This surge causes greater-than-usual voltage drop in the power lines supplying the current. Similar effects are responsible for the momentary dimming of lights that can occur in a house when an air conditioner or dishwasher motor starts.
I don't understand how voltage drop happens. Isn't the wiring of houses done such that every equipment is parallel to the power line? If it is done in parallel, shouldn't the voltage to every equipment be same? What I have understood is, at the beginning there is no back emf as the coil is not moving causing large amount of current to flow, which will cause less-than-usual current to flow from other equipment such as light bulb which causes its dimming. I think I am missing something important here. Any hints or help would be kindly appreciated!
Best Answer
If there's only one, you're way ahead of the rest of us.
Yes, but the power line itself has some resistance. Here's a simple model:
When one of the loads draws a very large current, it causes a drop across the feed line resistance, represented by R1 in my model.
Yes, that's why a drop caused by one load (say R1) can also affect the voltage seen by another load (say your overhead lights).
Yes, you're missing the step where the high current from the motor causes voltage drop across the feed line, which lowers the voltage available to the resistive loads. The lower voltage is what causes them to draw less-than-usual current.