Chapter 33

Why is direct current more difficult to interrupt that alternating current?

Because it does not fall to zero at periodic intervals

What is often employed to start small DC motors?

Fractional HP manual starters and magnetic starters that are generally used to control small AC motors

What is the purpose of the FCR?

The FCR ensures that current is flowing through the shunt field before voltage can be connected to the armature

Why are clapper type contactors generally used to control DC devices?

because they exhibit a greater air gap between the movable and stationary load contacts

What type of contactors are generally used to control DC devices?

clapper type

When a contactor employs the use of dual coils, how are the holding and pick up coils connected in relationship to each other?

parallel

How is inrush current to large DC motors often limited?

resistors connected in series with the armature

Describe the starting methods for small DC motors

started across the line because they have low inertia, this permits them to gain speed quickly, causing a rapid increase in CEMF to limit inrush current