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Exam 12: Two-Wire Motor Control

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Question 1

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The phrases no-voltage drop-out, or two-wire control circuit should indicate a possible safety concern to the electrician, because a mechanically held closed pilot device could automatically restart the load motor when the power is restored.

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Question 2

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Pilot devices control the motor starter control coil.

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Question 3

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Describe two-wired motor control circuits.

The pilot control device shuts down at a loss of power.

Differential controls provide a mechanical means, _______________ of the electrical control circuit.

A pilot device is the term given to any two-wire control circuit component that mechanically closes and opens its control contacts, depending on the state of the medium it is measuring.

No-voltage drop-out or two-wire control circuit should indicate a possible ____ to the electrician, because a mechanically held closed pilot device could automatically restart the load motor when the power is restored.

Two-wire control components are called ____ devices.

Two-wire motor control circuits are called two-wire because there are only two control circuit wires between the motor starter and the control device(s).

The purpose of a _____-automatic circuit is to give the operator three operating modes; a manual hand position, off, and an automatic position where the pilot device automatically controls the control coil.

An example of a differential control device is a(n) ______.

It is extremely uncommon to find differential switches for pilot devices in these motor control circuits.

_______________ motor control circuits only have two control circuit wires between the motor starter and the control device(s).

Differential controls provide a mechanical means that acts like a mechanical holding circuit.

Two-wire motor control circuits are extremely complex motor control circuits.

The pilot control device is a(n) _______________ control, which is unaffected by the loss of power.

The purpose of a hand-off-automatic circuit is to give the operator three operating modes; a manual hand position, off, and an automatic position where the pilot device automatically controls the control coil.

Two-wire control provides both no-voltage drop-out protection, or low-voltage drop-out protection.

What is the purpose of a hand-off-automatic circuit?

A differential control device is a two position (on/off) switch that actuates when the measured medium reaches either of the two pre-determined extreme high or low range values, with a dead zone in between where the switch does not change states.