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Commercial Refrigeration Ch 8 Questions and Answers (Graded A) $11.99
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Commercial Refrigeration Ch 8 Questions and Answers (Graded A)
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Commercial Refrigeration Ch 8 Questions and Answers (Graded A)Commercial Refrigeration Ch 8 Questions and Answers (Graded A)Commercial Refrigeration Ch 8 Questions and Answers (Graded A)Commercial Refrigeration Ch 8 Questions and Answers (Graded A) What are the two main weaknesses of 3Ø motors? -...

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  • September 19, 2024
  • 5
  • 2024/2025
  • Exam (elaborations)
  • Questions & answers

Subjects

  • commercial refrigeration ch 8 questions and answer
  • commercial refrigeration ch 8 answers
  • what are the two main weaknesses of 3ø motors

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  • Commercial Refrigeration Ch 8
  • Commercial Refrigeration Ch 8

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Commercial Refrigeration Ch 8
Questions and Answers (Graded
A)
What are the two main weaknesses of 3Ø motors? - ANSWER - Phase loss and
voltage unbalance.


What formula is used to measure the percentage of voltage unbalance? - ANSWER -
Vu = Vd / Va


The amperage load rating of a compressor contactor is listed under which rating,
the inductive rating or resistive load rating? - ANSWER - Inductive load rating


What indicates the contacts are bad on a contactor? - ANSWER - There is a voltage
rating across the contacts of the contactor when pulled in.


The contactor must be replaced whenever a 3Ø compressor is replaced. - ANSWER -
True


How is a motor starter different from a contactor? - ANSWER - A motor starter has
overloads


Why does a 1Ø motor need a phase shift to start the motor turning? - ANSWER - The
windings are 180 degrees out of phase; therefore, the stator and rotor have equal,
but opposite, attraction.


How does a 1Ø motor accomplish its phase shift? - ANSWER - The start winding has
more resistance, which causes a phase shift, creating a slightly different angle to
the magnetic pull of the stator.


Are the contacts (L-S) of a current relay normally open (NO) or normally closed
(NC)? - ANSWER - Normally Open

, Are the contacts (1-2) of a potential relay NO or NC? - ANSWER - Normally Closed


What is a good rhyme to remember the wiring terminals of a potential relay? -
ANSWER - 5, 2, 1, can she run?


What is the difference between the windings in a 3Ø motor and a 1Ø motor? -
ANSWER - A single phase motor has both start and run windings.


What are considered the "poles" of a motor? - ANSWER - The bundles of wires for
the start windings, or the run windings.


What is the nominal rpm of a two pole motor? A four pole motor? A six pole motor? -
ANSWER - 3,600, 1,800 & 1,200 RPM


During start up, as the compressor motor speed increases the amperage does
what? - ANSWER - Decreases


A motor draws locked rotor amps (LRA) only when the motor is mechanically locked
up. - ANSWER - False


What are the two basic functions of a start relay? - ANSWER - The start relay
provides full power to the start windings on start-up, and then de-energizes the
start windings when the motor is up to speed.


What are three types of start relays? - ANSWER - Current relay, Potential relay, and
Positive temperature co-efficient relay.


What size compressors use current relays? - ANSWER - Fractional HP compressors


On a current relay, what do the terminal designations L, M, and S stand for? -
ANSWER - Line, main winding, and start winding.

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