In Terms of Speed Control, How Does a Four-Terminal Starter

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The Answer is A four-terminal starter provides for variable speed control using a field rheostat. As the arm is raised to the first position, the shunt field receives full voltage, yet there is still resistance in the armature circuit. As the arm is moved to the right, resistance is added to the shunt field circuit but removed from the armature circuit. Because adding resistance to the shunt field circuit reduces the current to the field, the holding electromagnet is not in series with the shunt field but is connected across the line, hence the fourth terminal.

In Terms of Speed Control, How Does a Four-Terminal Starter

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