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100
What type of overcurrent is confined to the normal conductive path provided by the conductors, circuit devices, and loads of the distribution system?
Overload Condition
100
A 600-volt AC fuse or circuit breaker is considered to have a 600-volt DC rating, even if it is not marked with a DC voltage rating.
False
100
? are the most prevalent circuit breakers in use for 15 amperes to 2,500 amperes.
Molded case circuit breakers (MCCB)
100
Which is not one of the three different general fuse operating characteristics available?
Instantaneous
100
The “in sight from motor” disconnect is used to isolate the motor from the source of supply for maintenance work to create a(n) ? condition and serves as a(n) emergency disconnect.
electrically safe
200
Magnetic motor starters listed to UL 508 are suitable for use as ? .
motor overload protection and controllers
200
Which of the OCPDs below is a branch-circuit rated circuit breaker?
A
200
In general, a disconnecting means shall be located within ? the motor location and driven machinery location.
sight from
200
A disconnecting means is required to be in sight and readily accessible from the air conditioning or refrigeration equipment unless one of two exceptions are met per NEC ? .
440.14
200
Determine the maximum primary fuses for installation in a 250kVA, 3-phase, 13.2kV to 480/277-volt transformer with an impedance of 3.25%. The transformer is installed in an unsupervised location.
35 A
Solution:
Ipri = kVA x 1000 ÷ 13,200 V x 1.73
Ipri = 250,000 VA ÷ 22,836 = 10.95 amperes
10.95 amperes x 300% = 32.84 amperes
Next standard fuse ampere rating = 35 A
300
The primary fuses and circuit breakers can be sized at approximately 125%, or the next standard ampere rating, for the typical 480-volt to 208/120-volt, 15 kVA to 45 kVA dry type transformers used in commercial installations. This is because these transformers most often do not have high primary inrush currents. For actual installations, the transformer inrush characteristics should be considered.
True
300
Section 430.72 contains overcurrent protection requirements for motor control circuits, which includes motor control circuit conductor protection in 430.72(B) and motor control transformer protection in 430.72(C).
True
300
A series rated system, which is permitted by NEC section ? , is where a circuit breaker with an interrupting rating less than the available fault current is verified to be protected for available fault current greater than its interrupting rating by specific line-side fuses or circuit breaker–hence the term series combination rating, series rating, or series rating combination.
240.86
300
An all-fuse system is a ? system and current-limiting fuses (Class L, R, J, T, CF, CC) are fully rated at 200 kA or 300 kA. This is assuming that the available fault currents do not exceed the fuses’ interrupting ratings.
Fully Rated
300
A fully rated system is one in which all of the overcurrent protective devices have an individual interrupting rating ? the available fault current at the point of their application.
equal to or greater than
400
When tested, listed, and marked series rated combinations are used per ? , the series rated combination must be marked on the equipment enclosure (or provided by a bulletin affixed to the enclosure) by the equipment manufacturer, and per ? the series rated combinations to be utilized must be marked on the equipment by the installer.
240.86 / 110.22
400
Which is not a hazard associated with installing electrical equipment where the marked SCCR is less than the available fault current?
Cave-in
400
Below is the SCCR label for a power distribution block (PDB) that is to be installed in a wireway. The wires used will be 2 AWG on the line side and several 12 AWG wires on the load side. What is the maximum ampere rated Class J fuse that can be used on the line side of the PDB and provide short-circuit protection, if the available fault current is 20,000 amperes? Assume the system voltage is 208/120 volts and the PDB voltage rating is 600 volts. Do not consider the ampere rating needed based on load calculations.
200
400
Selective coordination of overcurrent protective devices decreases the reliability of the electrical distribution system to deliver power to the loads.
False
400
Selective coordination is achieved when OCPDs are chosen such that whenever an overcurrent occurs, not only does the nearest line-side OCPD open to interrupt the overcurrent, one or more upstream larger ampere rated OCPDs open.
False
500
To meet the selective coordination requirements of the NEC, the analysis and selection of the overcurrent protective devices to achieve selective coordination must be completed by an Electrical Worker.
False
solution:
645.27, 700.32, 701.32, 708.54
500
For a few large ampere circuits at certain voltage levels and with certain types of grounding systems, the NEC requires, in addition to the normal phase overcurrent protective devices, ? , which is/are intended to provide equipment protection from lower-magnitude ground-fault currents.
ground-fault protection of equipment
500
Ground fault relays monitor ? .
ground-fault current
500
Ground-fault protection of equipment is not permitted on circuit paths for ? .
fire pumps
500
When installing GFPE equipment using the residual sensor scheme, the neutral conductor is inadvertently installed with the incorrect polarity with respect to the associated phase conductors. This installation results in ? .
normal load current detected as a fault condition, which may result in a false GFPE trip