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Exam 21: The Cooling System

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Question 1

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When is the branch-circuit selection current marked?

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Some hermetic refrigerant motor compressors are designed to operate continuously at currents greater than 156 percent of the RLA.In such cases, the unit's nameplate is marked with "Branch­ Circuit Selection Current" or "Minimum Supply Circuit Conductor Ampacity." The MBCSC will be no less than at least 64.1 percent of the MCC rating of the hermetic refrigerant motor-compressor.Note: 156 percent and 64.1 percent have an inverse relationship.

Question 2

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The evaporator in a commercial installation normally consists of a coil, through which the building air is circulated by a motor-driven fan.

A) plate tube
B) helical tube
C) fin tube
D) fan plate

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Question 3

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The system for the drugstore and bakery is a system with the compressor and condenser located on the ground adjacent to the building and the evaporator located in an air-handling unit in the basement.

The tremendous popularity of mechanical refrigeration for household use in the 1930s and 1940s stimulated the development of a new series of nonexplosive and nontoxic refrigerants known as of the halogen family.

In most instances, the RLA is at least equal to percent of the hermetic refrigerant motor­compressor's maximum continuous current (MCC) .

Where is the expansion valve located, and how does it function?

Where was the initial demand for hermetic compressors and what were the implications of this?

A motor-compressor must be protected from overloads and failure to start by a time-delay fuse or inverse-time circuit breaker rated at not more than percent of the rated load current.

Can you cool your kitchen by leaving the refrigerator open? Explain why or why not.

Air-cooled condensers use to drive air across the condensing coil.

The hermetic compressor consists of a motor-compressor completely sealed in a gastight, casing.

compressors are usually used in large installations.

What does NEC 440.14 require of the disconnecting means in terms of location, access, installation, and mount?

Air-conditioning and refrigeration equipment is required by NEC 440.4(A) and (B) to be marked with a marked with the maker's name, the rating in volts, frequency and number of phases, and other information.

NEC 110.9 states that equipment intended to interrupt current at levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment.

The component of the refrigerant cycle raises the energy level of the refrigerant so that it can be condensed readily to a liquid.

____ is a method of removing energy in the form of heat from an object.

The compressor serves as a pump to draw the expanded refrigerant gas from the evaporator, boosts the of the gas, and sends it to the condenser.

The disconnecting means for an individual hermetic motor-compressor must not be less than percent of the rated load current or the branch-circuit selection current, whichever is greater.

Overload protection of the internal components is covered in the Standards.