Commercial Refrigeration Ch 8 (Compressor Motor Controls) Questions and Answers 100% Correct
7 views 0 purchase
Course
Commercial Refrigeration Ch 8
Institution
Commercial Refrigeration Ch 8
Commercial Refrigeration Ch 8 (Compressor Motor Controls) Questions and Answers 100% CorrectCommercial Refrigeration Ch 8 (Compressor Motor Controls) Questions and Answers 100% CorrectCommercial Refrigeration Ch 8 (Compressor Motor Controls) Questions and Answers 100% CorrectWhat are the two main w...
Commercial Refrigeration Ch 8
(Compressor Motor Controls)
Questions and Answers 100%
Correct
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.
, 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
Why does the cover on a compressor terminal box need to be left on? - ANSWER -
So the overload will properly sense motor temperature and open during an overload
condition.
How is a magnetic overload different from a thermo-disc type external overload? -
ANSWER - Magnetic overloads accurately respond only to the amperage and are not
affected by the ambient air temperature.
Why is it dangerous to jump out a compressor motor overload? - ANSWER - Without
the overload, there is no motor protection.
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
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller NursingTutor1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $11.99. You're not tied to anything after your purchase.
