Electricity level 3 section 5
UL Class R fuses have a short circuit interrupting rating of up to
200,000A
A feeder circuit with no motor load has a continuous load of 10A and a noncontinuous load of 10A. The feeder overcurrent protective device should be sized at
22.5A
To prevent the normal motor starting current from affecting the fuse operation, non-time-delay fuses can be sized at
300% of the motor full-load current
for 480V circuits, the arc current seldom exceeds
60% of the available bolted fault current
Which type of fuse should be used to prevent nuisance tripping from temporary motor overloads and surge currents?
Dual-element, time-delay fuse
Which of the following is within the basic scope of Underwriters Laboratories?
Safety
Which of the following is true with regard to circuit breaker interrupting capacity ratings?
UL tests now include NEMA ratings.
Where are the overcurrent protective devices normally installed in a branch circuit?
Where the conductors receive their supply
Equipment intended to interrupt current at fault levels must have an interrupting rating at nominal circuit voltage that is
equal to the current available at the line terminals of the equipment
A conductor with failed insulation contacts the metal edge of a grounded metal wire way. This is known as a(an)
ground fault
Which of the following are designed to withstand numerous trip and reset cycles without replacement and can be thermal, magnetic, or solid-state?
overload relays
The recommended method of detecting short circuit currents is the
point to point method
A feeder circuit with no motor lead has a continuous load of 5A and a noncontinuous load of 5A. the feeder overcurrent protective device should be sized at
11.25A
What is the maximum number of circuit breakers or sets of fuses that may be used as the service disconnecting means in a main service panel without a main switch?
6
If a 120v feeder for a nonmotor loads feeds a continuous load rated at 20A and a noncontinuous load at 30A, what size of overcurrent protective device should be selected?
60A
Which of the following is true of the voltage rating of a fuse?
It can be higher than the circuit voltage but never lower.
Types of fault current include overloads, short circuits, ground faults, and
arc faults
The thermal portion of a dual-element fuse
provides a trip delay for high levels of current
The magnetic portion of a standard circuit breaker
provides an instantaneous trip for high levels of current
Circuit breakers are classified by
the largest ampere rating of its range