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