District of Columbia Journeyman Electrician Practice Test

According to the NEC, what is the main purpose of the Code?

Article 90 states that the Code exists for the practical safeguarding of persons and property. It also says it is not a design specification or an instruction manual for untrained persons.

According to the NEC, how many services may a building generally be supplied by?

Section 230.2 limits a building to one service unless one of the listed special conditions applies (fire pumps, large loads, different characteristics and similar). Exceptions are ignored here.

According to the NEC, the conductors running from the main service panel of a house to a subpanel in a detached garage are:

Conductors between the service equipment and the final branch-circuit overcurrent devices (here, in the garage subpanel) are a feeder.

According to the NEC, which dwelling location requires GFCI protection for 125 V, 15 A and 20 A receptacles?

Section 210.8(A) lists bathrooms first among the dwelling locations that need GFCI protection for receptacles. Bedrooms, hallways and dining rooms are AFCI locations, not GFCI locations.

According to the NEC, what is the general rule for the conductors of one circuit, including the grounded conductor and EGC?

Section 300.3(B) keeps all conductors of the same circuit together to limit inductive heating and keep circuit impedance low.

According to the NEC, how must listed or labeled equipment be installed and used?

Section 110.3(B) ties the installation of listed or labeled equipment to the instructions that come with the listing or labeling.

A 10-hp, 460-V, three-phase motor has a nameplate current of 13 A. Which current is used to size its branch-circuit conductors?

Section 430.6(A)(1) requires the table full-load current (not the nameplate) for sizing conductors, switches and short-circuit and ground-fault protection of general motors.

A disconnect is required to be lockable in the open (off) position. What does the NEC require of the locking provision?

Section 110.25 requires the locking provision to remain in place with or without the lock installed; portable means that are removed with the lock do not qualify.

In the hazardous location system, what separates Class I, Division 1 from Class I, Division 2?

Under 500.5(B), Division 1 locations have ignitible concentrations under normal conditions; Division 2 locations have them only through abnormal events such as leaks or ventilation failure.

In one- and two-family dwellings, what is the maximum PV system dc circuit voltage the NEC permits?

Section 690.7 limits PV dc circuits to 600 V in one- and two-family dwellings and 1,000 V on or in other buildings.

According to the NEC, which installation is outside the scope of the Code?

Section 90.2 lists what is not covered, including utility-controlled installations used for generation, transmission or distribution. Conductors connecting premises to the supply are covered.

According to the NEC, may branch-circuit conductors be installed in the same raceway as service conductors?

Section 230.7 keeps other conductors out of service raceways and service cables (grounding conductors and bonding jumpers are allowed). Service conductors are unprotected on the line side, so other circuits are kept apart.

According to the NEC, unless the equipment is listed for 100% operation, feeder conductors must have an ampacity of at least the noncontinuous load plus what percentage of the continuous load?

Section 215.2(A)(1) requires the feeder ampacity to be at least the noncontinuous load plus 125% of the continuous load (before any adjustment or correction).

According to the NEC, in a dwelling, receptacles in a garage whose floor is at grade level must have:

Section 210.8(A) requires GFCI protection for receptacles in garages and in accessory buildings with a floor at or below grade not intended as habitable rooms.

According to the NEC, conductors of 120/240 V and 480Y/277 V systems may share a raceway when:

Section 300.3(C)(1) allows conductors of different systems of 1000 V or less in the same raceway, cable or enclosure if every conductor's insulation is rated at least the maximum voltage applied to any conductor there.

A knockout was removed from a panelboard but no raceway or cable was installed in it. According to the NEC, what must be done with the opening?

Under 110.12(A), unused openings other than those for mounting or drainage must be closed so the protection is substantially equivalent to the wall of the equipment.

Which current is used to size the separate overload protection of a general-purpose motor?

Section 430.6(A)(2) bases separate motor overload protection on the motor nameplate current rating.

Three-way and four-way switches must be wired so that all switching is done in which conductor?

Section 404.2(A) requires three-way and four-way switches to switch only the ungrounded circuit conductor.

A textile mill has easily ignitible fibers and flyings in the air. Which hazardous location class applies?

Section 500.5(D) defines Class III locations by ignitible fibers or flyings; Class I is gases and vapors and Class II is combustible dust.

Why is a PV string's maximum voltage figured at the lowest expected ambient temperature?

Section 690.7(A) corrects the rated open-circuit voltage for the lowest expected ambient temperature, because Voc increases as cell temperature falls.