Unit 19 Motor controls

what is not a typical voltage used for relays contactors and motor starters?

12V

What is the difference between a contactor and a starter

A Starter has over current protection built into its framework. (starters are contactors with over current protection devices).

Can a contactor always be converted to a starter

A contactor cannot always be converted to a starter, but in some cases it can. The starter differs from the contactor because of the over current protection

Can a motor be started immediately after an overload?

A motor should not be restarted immediately after an overload condition because they may need time to cool. When possible, determine the reason for the overload condition before restarting the motor.

Why is it not a good idea to file or sand the contactor contacts?

Contacts may be cleaned but this should be done as a temporary measure only. Filing or sanding exposes base metal under the silver plating and speeds deterioration. Replacing the contacts are the only recommended repair

Why is it not a good idea to use circuit protection devices to protect large motors from overload conditions?

Fuses protect circuits, not motors. With 2 motors, on the same circuit ... 1 motor can be operating in an overloaded condition, without overloading the conductor = fuse will not open the circuit

The difference between inherent and external overload protection

Inherent - motor overload protection is provided by sensing devices within the motor. External - motor overload protection is applied to the current passing device : the relay, the contactor, or the starter.

The two amperages that influence the choice for replacing a motor starter are

LRA (Locked Rotor Amperage) and FLA (Full Load Amperage)

what causes an overload protection device to function

Overcurrent

What are the contact surfaces or relays, contactors and starters made of?

Silver Cadmium Oxide

Under what conditions are motors allowed to operate with slightly higher than design loads

The motor can operate above the FLA and within the service factor (SLA) without harm

What components can be changed on a contactor and a starter for rebuilding purposes

The springs, the coil, and the overload protection device (heaters and switches)

magnetic overload devices are very accurate and not affected by ...... .......

ambient temperature

starters are .......... with motor ........... protection built into the framework of the contactor

contactors overload

external overload protection is applied to the ....... ......... device

current passing

contacts on relays, contactors, and starters should never be ........... or ...........

filed sanded

large motors should be protected from .......... conditions

overload

Two types of relays are

pilot duty and throw away

What is the purpose of overload protection at the motor

protect the motor from over current and damage

contactors are large ........ that may be ................

relays rebuilt

The recommended repair for a defective relay is to

replace it

inherent motor overload protection is provided by ....... devices within the motor

sensing

relay, contactor, motor starter are three types of motor ........ and ......... devices

starting stopping

the relay is used for ........... circuits and motor ........

switching starting

bimetal and solder pot devices are ............ operated

thermally