Questions and Answers
The fuse and circuit breaker are two types of automatic overload devices that are normally used in what?
Circuit breakers are classified into?
Ampere groupings and each group is classified by the largest ampere rating of its range.
The ampere rating of a circuit breaker is located where?
On the handle of the device.
Two organizations that both test and list devices are?
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Standard interrupting capacity circuit breakers can be identified by what?
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The FH-type circuit has an interrupting rating of?
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Standard interrupting capacity circuit breakers are used where?
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At currents below a threshold of about 1,000A, the current-limiting circuit breakers perform in a manner similar to what?
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UL defines Class A devices as?
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Class A devices must not trip below?
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A non-feed through type GFCI receptacle offers only protection at?
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Because single element fuses have a high speed of response to short circuit currents, they are particularly suited for protection of breakers with?
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What NEC Section requires that any cartridge fuses used for branch circuit or feeder protection must be plainly marked?
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NEC Section 240.6(C) requires you to show what on the fuse barrel?
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When sizing fuses for a given application....?
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Coordination is the name given to?
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Harsh environments, general deterioration, accidental damage, damage from natural causes, excessive expansions, and overloading of the electrical system are all factors that contribute to?
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Reliable protective devices prevent or minimize costly damage to?
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A short circuit is probably the most common cause of?
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Overloads are most often between?
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Continuous (sustained) overloads can result from?
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What two types of automatic overload devices are normally used in electrical circuits?
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What NEC sections contain the requirements for interrupting ratings and protection against fault current?
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A standard molded-case circuit breaker usually contains?
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On an overload, the circuit breaker opens itself, or trips. When tripped, the handle jumps to?
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Circuit breakers are classified into?
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Circuit breakers are classified by?
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The lowest ampere ratings of circuit breakers frame sizes are?
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The largest ampere ratings of circuit breaker frame sizes are?
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Circuit breaker voltage ratings must be?
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Circuit breakers have two types of current ratings. Those are?
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The ampere rating of a circuit breaker is located on?
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Generally, the circuit breaker current rating must be?
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Most overcurrent protective devices are labeled with?
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Interrupting rating of electrical equipment is divided into two parts:?
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Different methods to determine the short circuit requirements are?
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NEMA tests are?
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UL tests are?
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Currents between 7 to 15 times the rated current are handled as?
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Interrupting capacity of a circuit breaker is based on its?
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High interrupting capacity circuit breakers are used in places such as?
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Current-limiting circuit breakers operate extremely fast to provide?
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One of the chief causes of circuit breaker failure is?
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GFCIs are what Class of protective devices?
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When installed properly, GFCIs continuously monitor the current in the?
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If the GFCI senses a difference between the grounded and ungrounded conductors of more than 6mA, it will automatically trip the circuit and power is interrupted in?
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Shunt trip circuit breakers have a built-in electric coil that causes?
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Shunt trip circuit breakers are used for?
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Arc fault circuit breakers include electronics that monitor?
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Arc fault circuit breakers detect?
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Switched neutral breakers disconnect?
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Switched Neutral breakers can be installed in?
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Non-automatic breakers have?
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Non-automatic breakers can be used?
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A fuse is the simplest device for?
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Most low voltage distribution fuses have?
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Voltage rating of a fuse must be at least?
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Generally, the ampere rating of a fuse and switch combination should be selected at?
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The interrupting rating of most branch circuit, molded-case circuit breakers in service entrance boxes is?
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Current-limiting fuses have an interrupting capacity of 200,000A and are commonly used to protect?
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Edison base fuses are permitted only as?
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Type S fuses were developed to?
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All type S fuses are?
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Plug fuses are normally permitted to be used in circuits of no more than?
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A plug fuse is a?
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In most industrial and commercial applications, cartridge fuses are used because?
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Single element fuses have?
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Most fuses are used for protection of?
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Study Notes
Electrical Circuits and Protection Devices
- Fuses and circuit breakers serve as automatic overload devices in electrical circuits.
- Circuit breakers are categorized by ampere groupings, based on their maximum ampere ratings.
Circuit Breaker Identification and Ratings
- Ampere ratings of circuit breakers are indicated on their handles.
- Standard interrupting capacity circuit breakers feature black operating handles and labels.
- The FH-type circuit has a specific interrupting rating of 65,000A symmetrical at 240VAC.
- Typical use for standard interrupting capacity circuit breakers is in residential settings, usually where fault currents are below 10,000A.
Automatic Overload Device Classifications
- Class A devices, as defined by UL, trip at a ground fault current of 6mA or more but must not trip below 4mA.
- Non-feed through GFCI receptacles provide protection only at the installation point.
Fuse and Ground Fault Circuit Interruption
- Single element fuses react quickly to short circuit currents, making them optimal for protecting low interrupting rating breakers.
- NEC Section 240.6(C) mandates that cartridge fuses used for branch circuit protection be clearly marked with critical ratings including ampere and voltage.
Overcurrent and Fault Protection
- Coordination refers to the time-current relationship between multiple overcurrent devices in a system.
- Factors contributing to overcurrents include environmental conditions, equipment damage, and system overloading.
- Effective protective devices safeguard valuable components like transformers and motors from costly damage.
Short Circuits and Overloads
- Short circuits are common culprits of electrical issues, while overloads typically occur at one to six times the normal current.
- Continuous overloads can arise from defective motors or excessive loads on a circuit.
Interrupting Ratings and Capacity
- Interrupting ratings and fault current protection requirements are outlined in NEC Sections 110.9 and 110.10.
- Standard molded-case circuit breakers include components such as contacts and trip elements in insulated housing.
Ratings and Classifications of Circuit Breakers
- Circuit breakers must have ratings equal to or exceeding the system voltage they are connected to.
- Two primary ratings are continuous current and fault current interrupting capacity.
GFCI and Shunt Trip Devices
- GFCIs belong to Class A protective devices, monitoring current in grounded and ungrounded conductors.
- Shunt trip circuit breakers, featuring an electric coil, automatically open during an alarm or trigger from external devices.
Specialized Circuit Breakers
- Arc fault circuit breakers are designed to detect patterns indicating arcing, such as damaged cords.
- Switched neutral breakers cut power to the neutral conductor at the same time as the live conductors and can be used in fuel dispensing.
Fuse Characteristics and Applications
- Fuses serve as simple overload protection devices and must match or exceed the circuit's voltage rating.
- Current-limiting fuses can handle capacities up to 200,000A, commonly used for protecting lower-rated circuit breakers.
- Edison base fuses are only allowed as replacements in existing installations, while Type S fuses reduce over-fusing risks and are always time-delay types.
Fuses vs. Circuit Breakers in Applications
- Plug fuses are limited to 125V use and provide nonrenewable protection.
- Cartridge fuses are preferred in industrial settings due to their versatility in size and rating.
- Most fuses are primarily used for the protection of branch feeders operating at voltages of 600V or below.
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Description
This quiz focuses on electrical circuits and the role of protection devices such as fuses and circuit breakers. It covers identification, ratings, classifications, and typical applications in residential settings. Test your knowledge on the critical aspects of overload protection and safety standards in electrical engineering.