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Flashcards in Master Electrician Practice Exam Deck (85)
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1

Where conductor is marked RHW-2 on the insulation what does the "-2" represent?

The conductor has a maximum operating temperature of 90 degrees C

As indicated in Table 310.104(A), conductor insulation type RHW-2 and other types identified by the suffix "2" are rated 90º C for wet locations as well as dry and damp locations.

2

For a grounded electrical system supplied by a feeder or branch circuit, the equipment grounding conductor shall be sized in accordance with

The overcurrent protective device.

As per Section 250.32(B)(1), the equipment grounding conductor shall be sized in accordance with Section 250.122 which states the minimum size size equipment grounding conductor is to be selected from Table 250.122, which is based on the rating or setting of the feeder or branch-circuit overcurrent protective device.

 

3

Determine the allowable ampacity of a size 350 kcmil THW aluminum conductor installed in a raceway with four(4)  other current carrying conductors when the expected temperature is 44 degrees C

350 kcmil THW AL ampacity = 250 amperes before derating
250 amps x .82 (temp. correction) x .8 (adjustment factor) = 164 amperes

 

4

Determine the maximum number of 125 volt, general-purpose duplex recptacles the NEC permits to be protected by a 20-ampere, 120-volt single-pole circuit breaker in a commercial building.

13 receptacles

In accordance with Section 220.14(I), the load of 180 VA is applied to duplex receptacles mounted on a single yoke or strap. To determine how many receptacles are permitted to be on one circuit, first find the VA of the circuit:

120 volts x 20 amperes = 2,400 VA (circuit)

Then divide the VA of the circuit, 2,400 VA, by the VA of one receptacle,

180 VA: 2,400 VA (circuit) ÷ 180 VA (1 receptacle) = 13 receptacles

5

For lighting systems operating at 30-volts or less, the output circuits power supply are to be rated for NOT more than ____.

25 amperes

Article 411 addresses low-voltage lighting systems. It is intended to cover low-voltage interior lighting and low-voltage landscape lighting installations. Section 411.2 states, for lighting systems operating at 30 volts or less, the output circuits of the power supply are to be rated for not more than 25 amperes.

6

Where there are tenant spaces in retain shopping mall, each occupant shall have access to the main disconnecting means, EXCEPT:

Where the service and maintenance are provided by the building managment.

 

The intent of Section 240.24(B)(1)(1) is to recognize in some situations it is better to have the building management have control of the overcurrent devices than the tenant. Where the electrical service and electrical maintenance are provided by the management and are under continuous building management supervision, the overcurrent devices shall be permitted to be accessible to authorized management personnel only.

7

Determine the conductor allowable ampacity when give the following related information:

*ambient temperature of 44 C

*250 kcmil THWN copper conductors

*four (4) current-carrying conductors in the raceway

*length of raceway is 50 feet

167 amperes

250 kcmil THWN copper ampacity = 255 amperes before derating
255 amps x .82 (temp. correction) x .8 (adj. factor) = 167.28 amperes

 

8

In general, the grounded conductor and the grounding conductor must be bonded together in ____.

I.  panelboards used as service equipment 

II. all sub-panels

Panelboards used as service equipment 

 

As mandated in Section 250.24(A) the grounded service conductor of an ac electrical system shall be connected to the grounding electrode conductor at each service. The purpose of this grounding method is to limit the voltage to ground imposed on the system by lightning and line-surges. This grounding connection also stabilizes the voltage to ground during normal operation, including short-circuits. Section 250.24(A)(5) prohibits re-grounding of the grounded conductor on the load side of the disconnecting means. This requirement prevents parallel paths for neutral current on the load side of the disconnecting means.

9

Using the standard method of calculation, what is the demand, in KW, on the ungrounded (line) service-entrance conductors of an apartment complex that has 35 electric ranges rated at 11.5 kW each?

50 KW

When using the standard method of calculation for dwellings, in accordance with Section 220.55, the use of Table 220.55 is permitted when determining the demand loads for household cooking appliances on service-entrance and feeder conductors. It is unlikely all cooking appliances will be in operation simultaneously and Table 220.55 was developed based on utility demand that proves this point.

Since the ranges in this question have a kW rating of more than 8¾ and less than 12, apply the values given in Column C of Table 220.55 as shown:

35 ranges = 15 kW + 35 kW (1 kW per range) = 50 kW demand

 

10

Electrical services and feeders of a recreational vehicle park shall be calculated on the basis of NOT less than ____ per RV site equipped with (1) 50 ampere 120/240 volt receptacle, (1) 30 ampere 120-volt receptacle and (1) 20 ampere 120-volt receptacle.

9600 VA

120*50= 6000 VA

120*30=3600 VA

120*20=2400 VA

6000VA

3600VA

2400VA

12,000 VA *.8=9600 VA

Section 551.73(A) requires where RV sites are equipped with 50-ampere, 120/240, receptacles, they are to be calculated on the basis of not less than 9600 volt-amperes. Also, where the RV site has more than one receptacle, the calculated load shall be calculated only for the highest rated receptacle.

 

11

Where applying the optional method of calculation for a one-family dwelling, what is the demand load, in kW, for the heating and cooling equipment, on the ungrounded service-entrance conductors for a residence that has the following?

*one blower rated 1.2kW, interlocked with both space heating and AC equipmen

*one central electric space-heating unit rated 25kW

*one air-conditioning unit rated 6.6kW

17.03 KW

 

For loads that do not operate simultaneously, Section 220.60 permits the total load to be calculated based on the largest load being considered. This requirement is also addressed in Section 220.82(C). As per Section 220.82(C)(4), the central space heating load is required to be based on only 65% of the heating equipment load(s).

*NOTE - Use the larger of the A/C or heating load.
25 kW (htr.) + 1.2 kW (blower) = 26.2 kW x 65% = 17.03 kW demand

12

Apply the general method of calculation of dwelling unit and determine the MINIMUM demand load, in VA, where one-family residence has the following fastened in place appliances.

*microwave oven -1250VA

*trash compactor -960VA 

*dishwasher-1400VA

*garage door opener-960VA

3,428 VA

When using the general method of calculation for dwellings, Section 220.53 permits a demand factor of 75% to be applied to the nameplate rating load of four or more appliances fastened in place, other than ranges, clothes dryers and heating and AC equipment.

microwave oven -      1,250 VA
trash compactor-        960 VA
dish washer -             1,400 VA
garage door opener- 900 VA 
                                   4,570 VA x 75% (demand) = 3,428 VA

13

Where a service riser is installed in wet Location and contains THWN insulated conductors, the wiring method used ____.

Permitted 

(1) Type IGS cable.
(2) Rigid metal conduit.
(3) Intermediate metal conduit.
(4) Electrical metallic tubing.
(5) Metallic wireways.
(6) Busways.
(7) Metallic auxiliary gutters.
(8) Rigid nonmetallic conduit, underground. (9) Mineral-insulated, metal-sheathed cable.

(10) Flexible metal conduit not over 1.83 m (6 ft) long or liquidtight flexible metal conduit not over 1.83 m (6 ft) long between raceways, or between raceway and service equipment, with equipment bonding jumper routed with the flexible metal conduit or the liquidtight flexible metal conduit according to the provisions of Section 250.102(A), (B), (C), and (E).

Service entrance conductors shall not run within the hollow spaces of frame buildings.

14

What is the Maximum distance between supports for straight horizontal runs of trade size 1 1/2 inch threaded rigid metal conduit (RMC)?

 

14 feet

Table 344.30(B)(2) shows horizontal runs of threaded trade size 1½ in. rigid metal conduit to be supported at least every 14 ft.

15

Overcurrent protection of transformers, of 600 volts or less is required to be sized.

In accordance with Table 450.3(B)

Section 450.3(B) requires overcurrent protection of transformers of 600 volts or less to be provided in accordance with Table 450.3(B)

 

16

A thermal barrier shall be required if the space between the resistors and reactors, of 600 volts or less, and combustible material is Less than ____.

12 inches

Because resistors and reactors give off heat, they must be guarded and located at safe distances from combustible material. A thermal barrier is required if the space between the resistors and reactors and any combustible material is less than 12 in. Refer to Section 470.3.

17

In movie theaters, all switches for controlling the emergency lighting systems shall be located _____.

In the lobby.

in compliance with Section 700.21, in theaters, all switches for controlling emergency lighting systems shall be located in the lobby or at a convenient accessible location. The switches are not permitted to be placed in the projection both or on the stage.

18

Where a 90 amper, 240-volt, single-phase load is located 225 feet from a panelboard and is supplied with 3 AWG copper conductors, determine the approximate voltage drop on the conductors. (K=12.9)

10 Volts

To calculate the voltage drop on this circuit, first locate the circular mil of the conductors (52,620 CM) as indicated in Table 8 of Chapter 9. Then apply the single-phase voltage drop formula:

VD = 2KID VD = 2 x 12.9 x 90 amps x 225 ft. = 9.92 volts dropped
             CM                   52,620 CM

 

19

A one-family residence is served with insulated 120/240 volt service-drop conductors, supported with a grounded messenger wire from the utility company.  The service-drop crosses the swimming pool; the pool has a diving board with 5 feet above water level. The NEC requires the conductors to be a minimum height of ___ above the pool water level.

22 1/2 feet

When taking these conditions in consideration, Table 680.8 and Figure 680.8 show the conductors are required to have a clearance of not less than 22½ ft. above the water level of the pool. These clearances consider factors as the use of skimmers with aluminum handles during pool maintenance and provide sufficient separation between the overhead conductors and the swimming pool.

 

20

All metallic switchgear rated for over 600 volts shall be provided with a grounding busbar for the purpose of connecting the

Metallic shield of cables.

The purpose of connecting the metallic shield of cables to the grounding busbar is to limit the voltage to ground imposed on the system by lightning and line-surges. This grounding connection also stabilizes the voltage to ground during normal operation, including short-circuits.

21

Conductors tapped from a feeder and supplying the primary of a transformer need to have overcurrent protection, where the length of the tap conductors are not over 25 feet and have an ampacity of at LEAST ____ of the rating of the overcurrent device protecting the feeder conductors.

One-Third

As permitted by Section 240.21(B)(3)(1), the tap conductors supplying the primary of a transformer need not have overcurrent protection where the conductors have an ampacity at least one-third the rating of the overcurrent device protecting the feeder conductors. This installation is permitted where the conductor length of 25 ft. is applied to one primary and one secondary conductor and the conductors are protected from damage by being enclosed in an approved raceway.

 

22

Electrical equipment such as switchboards, panelboards, industrial control panels, and motor control centers, located in commercial and industrial occupancies are required to be field marked to warn ____ of potential electrical arc flash hazards.

qualified persons

Section 110.16 was initiated to require electrical equipment to be field marked to warn electricians of potential electrical arc flash hazards when working on energized (hot) equipment.

23

When connecting utilization equipment to a 20-ampere rated branch-circuit that also serves luminaires, the utilization equipment shall have an ampere rating of NOT more than ____.

10 Amps

Section 210.23(A)(2) permits a 15- or 20-ampere branch circuit supplying lighting outlets to also supply fastened in place utilization equipment, such as an appliance. The utilization equipment load must not exceed 50% of the branch-circuit ampere rating.

20 amperes x 50% = 10 amperes

 

24

Where a hotel has a stationary electric sign installed inside a decorative fountain, the sign shall be at LEAST ____ inside the fountain, when measuring from the outside edges of the fountain.

5 feet

The intent of Section 680.57(C)(1) is to prevent contact with the electric sign by unauthorized people around the fountain.

25

In an aircraft hanger, the area that extends upward from the floor level ____ above the upper surface of aircraft wings, power plants and fuel tanks shall be classified as a Class 1, Division 2 or Zone 2 location.

5 feet

Section 513.3(C)(1) covers the classification of areas in the vicinity of aircraft housed in aircraft maintenance and storage hangers. In order to properly classify hanger areas, the dimensions of the aircraft within the hanger must be known.

26

Conductors supplying outlets for arc an xenon motion picture projectors of the professional type shall be a minimum size of ______.

8 AWG

Section 513.3(C)(1) covers the classification of areas in the vicinity of aircraft housed in aircraft maintenance and storage hangers. In order to properly classify hanger areas, the dimensions of the aircraft within the hanger must be known.

27

Where rigid polyvinyl chloride (PVC) conduit is installed underground to supply a gasonline dispensing unit, threaded rigid metal conduit (RMC) or threaded intermediate conduit (IMC) shall be used for the LAST ____ of the underground run to where the conduit emerges.

2 FEET

Exception No. 2 to Section 514.8, makes it clear that, where Type PVC conduit is used for underground wiring supplying motor fuel dispensers, threaded rigid metal conduit or threaded intermediate metal conduit must be used for the last 2 ft. of the underground run to where the conduit emerges.

28

Where electrical metallic tubing (EMT) is installed under metal-corrugated sheet roofing decking, a clearance of at least ____ must be maintained between the top of the tubing and the surface of the roof decking.

1 1/2 inches

Section 300.4(E) recognizes boxes or raceways located below metal-corrugated roof decking may be damaged by nail or screw penetration during construction. Therefore, a clearance of at least 1½ in. must be maintained between the decking and the boxes or raceways.

 

29

After applyin all demand factors, the ampacity of the service-entrance conductors are required to be NOT less than ___ where both the overcurrent device and its assembly are not listed for operation at 100 percent of their rating.

The sum of the noncontinous loads plus 125 percent of the conitinous loads

The purpose of the rule addressed in Section 230.42(A)(1) is to prevent the overheating of the service-entrance conductors. The ungrounded service-entrance conductors must have an allowable ampacity of 100% of the noncontinuous loads plus 125% of the continuous loads to be served.

 

30

When an equipment room houses electircal equipment rated at LEAST ____ or more, the personnel doors intended for entrance to an from egress from working space, shall open in the direction of egress.

1200 amps 

The requirements presented in Section 110.26(C)(3) are intended to provide access to electrical equipment. However, the primary intent is to provide egress from the area so that workers can exit through doors equipped with panic bars in the event of an arc-flash incident.