HVAC

Electrical energy conversion devices (loads) are manufactured to tolerate a voltage of?

+/- 10%

(T or F) An opposed magnetic field is produced in the rotor by a process called "induction".

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(T or F) Dual-voltage motors have 2 separate run windings.

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(T or F) The start winding has no other purpose than to provide automatic starting of an electric motor.

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Capacitors are always connected in ______ to the start winding.

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How is the direction of rotation changed on a 3 phase motor?

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Motor speed is determined by the number of stator ______.

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Name 3 methods used to check a capacitor.

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Name 5 types of single-phase induction motors.

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Name the 2 most common motor problems.

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Name the 3 electrical terminals located on a hermetic motor-compressor.

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On a hermetic compressor, why is the switch to disconnect the start winding located outside the shell?

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The PSC motor uses a ______.

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The motor windings are located in the ______.

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The start winding must be disconnected at about _____% of normal motor speed.

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What do the abbreviations LRA and FLA stand for?

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What is the only difference between a split phase motor and a CSIR motor?

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What test meter is used to check a motor for a short to ground or open winding?

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Which of the motor windings determines direction of rotation?

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Residential lighting and receptacles use.......

120V single phase

What should a transformer be oversized by?

125%

Most residential units have 2 hot wires and a neutral wire: What is the supplied voltage? How many phases are supplied?

240V Single phase

Which transformer, single phase or 3 phase has a better power factor?

3 phase

Many motors and other devices are limited to a ____% voltage tolerance.

5%

Transformers are _____% to _____% efficient.

96 - 98%

What does a transformer's laminated core provide?

A circuit for the magnetic field.

An advantage of Alternating Current is........

AC can be: GENERATED at one voltage transmitted at a HIGHER VOLTAGE reduced to a lower voltage at the POINT OF USE

How does a transformer work?

AC current flows in the primary winding, and an alternating magnetic field is established in the laminated soft iron core. This induces an AC in the secondary winding. The magnetic field cuts across the turns of both windings and induces the same voltage in each turn of the two windings. The induced voltage is proportional to the number of turns in each winding.

In addition to primary and secondary voltages, transformers are selected by the _______ that the secondary winding can safely carry.

Amperage

What two ratings determine the physical size of a cartridge fuse?

Amperage and voltage ratings

Why does an overloaded or undersized transformer burn out?

Because the secondary coil cannot carry the current.

Overcurrent in the form of an overload or short circuit is described as......... Overloads can range from _____ to _____ times the normal current.

Current in excess of the normal flow for a given circuit. 2 to 10

What are the 2 types of 3 phase transformers?

Delta and Wye

What determines the voltage at the secondary (output) winding?

Determined by the number of coils or wraps versus the number of coils in the primary (input) winding.

What is the Operating Principle for a transformer?

Electrical energy can be efficiently transferred from one winding to another by magnetic induction.

Cycling on the overload can be cauised by......

Excess amperage draw Excess motor heat Excess compressor heat

What causes an overload? An overload is usually confined to the _____ wiring.

Excessive loads in the circuit, loose connections, and dry motor bearings. Circuit

What is used to protect a transformer?

Fuse

Name the two devices that protect against over-current.

Fuses and circuit breakers

A transformer's primary terminals are labeled as......

H1, H2, H3, etc

What is the "stinger leg"? The "stinger leg" is also called? How is it identified?

Higher voltage leg "high leg" Color-coded orange

Does a Step-up transformer increase or decrease voltage?

Increase voltage

Step up transformers make it possible to _____ voltage. Step down transformers make it possible to _____ voltage.

Increase voltage Decrease voltage

What is Power Factor?

Measure of transformer capacity

How does the GFCI work?

Monitors current flow in both the hot wire and neutral wire and is very sensitive to any imbalance.

Single phase transformers that offer a choice of voltages are called...........

Multi-tap transformers

What is a "dead leg" system?

One corner of the delta transformer (the dead leg) is grounded. Voltage from the dead leg to ground = 0 volts

What are the benefits of a multi-tap transformer?

One transformer can serve several applications.

What are the three types of fuses?

Ordinary, Time-delay, and Type-S

What happens when too much current flows through a wire? What happens to the wire?

Overcurrent It gets hot, damaging or destroying the insulated covering.

Electricity produced in three phases is called...

Polyphase generation

GFCI protects people against a.............

Potentially hazardous ground fault

What do fuses and circuit breakers do?

Protect against overcurrent. Designed to stop the flow of current when it exceeds safe limits.

What is the Ground Fault Circuit Interrupter (GFCI) designed to do?

Protect the circuit from overcurrent and protects people from potentially hazardous ground faults.

What does Oversizing a transformer do?

Protects it from becoming overloaded.

Name 2 main parts of an electric motor?

Rotor and stator

What are the two types of transformers?

Step up or Step down

What type of transformer has fewer coils in the secondary winding and produces a lower output voltage?

Step-down transformer

What type of transformer has more coils in the secondary winding and increases output voltage?

Step-up transformer

(T or F) Single phase power can be obtained from a 3 phase system.

TRUE. Single phase obtained from 3 phase by using just 2 hot wires or 1 hot and a neutral.

(T or F) A dual-element plug fuse should be used in circuits serving electric motors.

TRUE: Time delay fuses are necessary when fusing a circuit with an electric motor.

What is Ampacity?

The amount of current a wire can safely carry.

(T or F) Loads and other electrical equipment connected to the transformer secondary MUST match the voltage supplied by the transformer.

True

Single phase transformers are rated by?

VA (Volts x Amps) Volts x Amps x 125% = VA

How is Power Factor determined?

VA x 1.73

What is the most popular 3 phase transformer?

Wye

A transformer's neutral terminal is labeled as.....

X0

A transformer's secondary terminals are labeled as.....

X1, X2, X3, etc

A transformer consists of...........

two copper windings (coils) electrically separated from each other. The coils are wound around a core of laminated soft iron sheets.