26210 STUDY GUIDE
If the GFCI sense a difference between the grounded and ungrounded conductors of more than 6mA, it will automatically trip the circuit and power is interrupted in?
1/40 of a second or less.
The interrupting rating of most branch circuit, molded-case circuit breakers in service entrance boxes is?
10,000A.
The largest ampere ratings of circuit breaker frame sizes are ?
100A, 225A, 400A, 1,000A, and 2,000A frames.
Generally, the ampere rating of a fuse and switch combination should be selected at?
125% of the load current.
Plug fuses are normally permitted to be used in circuits of no more than?
125V between phases.
The lowest ampere ratings of circuit breakers frame sizes are ?
15A, 125A, 250A, 500A, and 1,200A
Most low voltage distribution fuses have?
250V or 600V ratings(other ratings are 125V and 300V).
Class A devices must not trip below?
4mA.
The FH-type circuit has an interrupting rating of?
65,000A symmetrical to 240VAC.
A standard molded-case circuit breaker usually contains?
A set of contacts, magnetic trip element, a thermal trip element, line and load terminals, bussing used to connect these individual parts, and an enclosed housing of insulated material.
Single element fuses have?
A very high response rate to overcurrents.
Circuit breakers are classified into what?
Ampere groupings and each group is classified by the largest ampere rating of its range.
Circuit breakers are classified into?
Ampere groupings that match specific physical dimensions, commonly referred to as frame size.
NEC Section 240.6(C) requires you to show what on the fuse barrel or a label attached to the barrel?
Ampere rating, voltage rating, interrupting rating, current limiting(where applicable), the name or trademark of the manufacturer.
Different methods to determine the short circuit requirements are?
Approximate values, extensive computations, and the point by point method(most simple method).
Most fuses are used for protection of?
Branch feeders on systems operating at 600V or below.
UL tests are ?
Certified by unbiased witnesses.
GFCIs are what Class of protective devices?
Class A.
Circuit breakers have two types of current ratings. Those are?
Continuous current rating and fault current interrupting capacity.
At currents below a threshold of about 1,000A, the current-limiting circuit breakers perform in a manner similar to what?
Conventional thermomagnetic circuit breakers.
Interrupting rating of electrical equipment is divided into two parts:?
Current at fault(short circuit) levels and current at operating levels.
Arc fault circuit breakers include electronics that monitor?
Current flow in the breaker.
Current-limiting circuit breakers operate extremely fast to provide?
Downstream protection for other types of overcurrent devices. Available for use where circuits are highly sensitive to amperage changes.
The fuse and circuit breaker are two types of automatic overload devices that are normally used in what?
Electrical Circuits
A short circuit is probably the most common cause of?
Electrical Problems.
Circuit breaker voltage ratings must be?
Equal to or greater than the voltage of the electrical system on which they are used.
Generally, the circuit breaker current rating must be ?
Equal to or less than the load circuit conductor current carrying capacity(ampacity).
Voltage rating of a fuse must be at least?
Equal to the circuit voltage. It can be higher but never lower.
Switched Neutral breakers can be installed in?
Fuel dispensing equipment.
What two types of automatic overload devices are normally used in electrical circuits?
Fuse and circuit breakers.
When installed properly, GFCIs continuously monitor the current in the ?
Grounded and ungrounded conductors.
One of the chief causes of circuit breaker failure is?
High heat caused by loose connections at the load side of the breaker.
Standard interrupting capacity circuit breakers are used where?
In residential applications where the available fault current is seldom higher than 10,000A.
High interrupting capacity circuit breakers are used in places such as?
Industrial plants.
Shunt trip circuit breakers have a built in electric coil that causes?
It to open the breaker contacts when the coil is energized.
Because single element fuses have a high speed of response to short circuit currents, they are particularly suited for protection of breakers with?
Low interrupting ratings.
Current-limiting fuses have an interrupting capacity of 200,000A and are commonly used to protect?
Lower rated circuit breakers.
Continuous(sustained) overloads can result from ?
Motor defects(such as worn motor bearings), overloaded equipment, or too many loads on a circuit.
What NEC Section requires that any cartridge fuses used for branch circuit or feeder protection must be plainly marked, either by a label attached to the barrel?
NEC Section 240.6(C).
What NEC sections contain the requirements for interrupting ratings and protection against fault current?
NEC Sections 110.9 and 110.10.
Non automatic breakers have ?
No devices to protect the circuit against overcurrent.
A plug fuse is a ?
Nonrenewable fuse.
Most overcurrent protective devices are labeled with?
Normal current rating and interrupting rating.
The ampere rating of a circuit breaker is located where?
On the handle of the device.
UL defines Class A devices as?
One that will trip when a fault current to ground is 6mA or more.
Overloads are most often between?
One to six times the normal current level.
A fuse is the simplest device for?
Opening an electric circuit when excessive current flows due to an overload or such fault conditions as grounds or short circuits.
Currents between 7 to 15 times the rated current are handled as?
Overcurrents by the thermal magnetic trip element.
Arc fault circuit breakers detect?
Patterns of surges or spikes typical of currents in a short, high resistance arcing circuit, such as a frayed electrical cord or loose connection.
Interrupting capacity of a circuit breaker is based on its?
Rated voltage.
Type S fuses were developed to?
Reduce the possibility of over-fusing a circuit.
Edison base fuses are permitted only as?
Replacements in existing installations.
NEMA tests are?
Self-certification tests.
Two organizations that both test and list devices are?
The UL and Canadian Standards Association.
The ampere rating of a circuit breaker is located on ?
The handle of the device.
Circuit breakers are classified by ?
The largest ampere rating of its range.
On an overload, the circuit breaker opens itself, or trips. When tripped, the handle jumps to?
The middle position.
Switched neutral breakers disconnect?
The neutral or ungrounded conductor simultaneously with all ungrounded conductors.
Harsh environments, general deterioration, accidental damage, damage from from natural causes, excessive expansions, and over-loading of the electrical system are all factors that contribute to?
The occurrence of such overcurrents.
A non-feed through type GFCI receptacle offers only protection at?
The point of installation.
Coordination is the name given to?
The time-current relationship among a number of overcurrent devices connected in series, such as fuses in a main feeder, subfeeder, and branch circuits.
Standard interrupting capacity circuit breakers can be identified by what?
Their black operating handles and black printed interrupting labels.
In most industrial and commercial applications, cartridge fuses are used because ?
They have a wider range of types, sizes, and ratings than plug fueses.
All type s fuses are?
Time delay fuses.
Reliable protective devices prevent or minimize costly damage to?
Transformers, conductors, motors, equipment, and many other components that make up the complete electrical system.
When sizing fuses for a given application....?
a single-line schematic will suffice.
Non automatic breakers can be used?
as a means of manually disconnecting circuits by operating the handle.
Shunt trip circuit breakers are used for?
fire suppression circuits, pushbuttons, or alarm circuits.
