Chapter 12 Contactors and Magnetic Motor Starters

It is estimated that every ___°C rise over normal ambient temperature ratings for insulation can reduce the life expectancy of a motor by almost a year.

1

___ overload relays are extremely quick to reset because they do not require a cooling-off period before being reset.

Magnetic

___ are used to reduce the distance required and yet quench arcs quickly.

Magnetic blowout coils

___ action is the principal operating mechanism for magnetic contactors.

Solenoid

___ control provides low-voltage release and low-voltage protection.

Three-wire

___ state a problem, its possible cause(s), and corrective action(s) that may be taken.

Troubleshooting guides

A(n) ___ overload relay is an overload relay that resets automatically.

bimetallic

A ___ is an overcurrent protection device with a mechanism that automatically opens the circuit when an overload condition or short circuit occurs.

circuit breaker

A ___ is a device used only periodically to remove electrical circuits from their supply source.

disconnect

A ___ alloy is a metal that has a fixed temperature at which it changes directly from a solid to a liquid state.

eutectic

For fully reliable motor protection, heat coils should be selected based on the motor ___ rating shown on the motor nameplate.

full-load current

A(n) ___ is the arrangement of contacts in such a way that both sets of contacts cannot be closed at the same time.

mechanical interlock

Originally, most knife switches were made of ___, which required replacement after repeated arcing, heat generation, and mechanical fatigue.

Copper

A ___ is used to change the amount of current flowing to a motor but reduces the current to a lower value for the overload relay.

current transformer

Contactor and magnetic motor starter modification devices include additional electrical contacts, power poles, pneumatic timers, transient suppression modules, and ___.

control circuit fuse holders

A(n) ___ coil converts the excess current drawn by a motor into heat, which is used to determine whether the motor is in danger.

heater

A(n) ___ motor protector is an overload device located directly on or in a motor to provide overload protection.

inherent

A motor that is starting draws a tremendous ___ current (normally six to eight times the running current) when the circuit is closed.

inrush

Additional NC contacts are used to turn on additional loads anytime a contactor or starter is OFF, as well as to provide electrical ___.

interlocking

A ___ rotor is a condition when a motor is loaded so heavily that the motor shaft cannot turn.

locked

AC manual starters are selected based on phasing, voltage, starter size, enclosure type, and ___.

number of poles

A(n) ___ was an improvement made to the original design of a knife switch.

operating spring

Loose connections in the power circuit of contactors and motor starters cause ___.

overheating

Normally, only one ___ unit with one or two contacts is added per contactor or motor starter.

power pole

The T-frame used with a 3Φ manual contactor is activated by a ___ mechanism.

pushbutton

The ___ indicator on a trip indicator informs the operator or electrician why the unit is not operating and that it is potentially capable of restarting with an automatic reset.

red (can be other colors though)

Two-wire control is normally used for ___ installations where an immediate return to service after a power failure is required.

remote or inaccessible

An advantage of ___ contacts is that the oxide (rust) that forms on the metal is an excellent conductor of electricity.

silver alloy

AC contactor assemblies are made of laminated ___, while DC assemblies are solid.

steel

Manual contactors are normally used ___.

with lighting circuits

What are the steps troubleshooting contactors and motor starters?

1. Inspect the motor starter and overload assembly 2. Reset the overload relay if there is no visual indication of damage 3. Observe the motor starter for several minutes if the motor starts after resetting the overload relay. 4. Check the voltage into the starter if resetting the overload relay does not start the motor. 5. Energize the starter and check the starter contacts if the voltage into the starter is present and at the correct level. 6. Check the overload relay if voltage is coming out of the starter contacts.

When troubleshooting a contactor or motor starter, the voltage is acceptable if the voltage reading is within ___% of the motor voltage rating.

10

If a motor has an FLC rating of 10 A with an SF of 1.15, the excess short-term current equals ___ A.

11.5

Transient suppression modules normally consist of resistance/capacitance (RC) circuits and are designed to suppress the voltage transients to approximately ___% of peak coil supply voltage.

200

A ___ V, 1Φ power source has two hot wires, L1 and L2 (ungrounded conductors), and no neutral.

230

Overload relay devices are normally rated to trip at a specific current when surrounded by an ambient temperature of ___°C.

40