Journeyman Electrician - Test 3 - 2014 NEC

Section 517.18(B) requires the minimum number of receptacles required for each patient bed location of health care facilities is eight. All the receptacles are to be listed "hospital grade" and the grounding terminal is required to be connected to an insulated copper equipment grounding conductor. As per 517.18(A) each patient bed location in general care areas shall be supplied by at least two branch circuits, one from the critical branch and one from the normal system. This requirement ensures power to be available upon the interruption of the normal power source.

As provided by Section 250.102(C)(1) the supply-side bonding jumper is not to be smaller than the sizes shown in Table 250.102(C)(1), which is based on the size of the largest ungrounded service-entrance conductor. In this situation the ungrounded service-entrance conductors are 2/0 AWG copper, therefore the bonding jumper is required to be 4 AWG copper.

The purpose of Section 300.6(A) is to provide ferrous metal conduit with corrosion protection with the application of an approved anti-corrosion compound where the conduit is threaded in the field.

When conductors are installed in parallel, to avoid excessive voltage drop and ensure equal division of current, different phase conductors must be located close together and each phase conductor, grounded conductor, and the grounding conductor must be grouped together in each raceway or cable. Section 310.10(H)(2)(1) requires all conductors of the same phase be the same length, and Section 310.10(H)(2)(3) requires the conductors to be the same size in circular mil area.

Before derating, Table 310.15(B)(16) shows the ampacity of 1/0 AWG THW copper conductors to be 150 amperes, which is to be multiplied by 80% [selected from the adjustment factors for more than 3 current-carrying conductors in the raceway shown in Table 310.15(B)(3)(a)]. Therefore, the allowable ampacity of the conductors is reduced to 120 amperes.

150 amperes x 80% (adjustment factor) = 120 amperes

To prevent corrosion of aluminum grounding electrode conductors, where used outside, they are not permitted to be terminated within 18 in. of the earth. Refer to Section 250.64(A).

As shown in Table 430.248 the full-load current rating of the motor is 28 amperes. This value is to be used when sizing the overcurrent protective devices from Table 430.52, which shows nontime-delay fuses are to be sized at not more than 300% of the FLC of the motor. 28 amperes x 300% = 84 amperes. According to Section 240.6(A), this is not a standard size fuse rating therefore, Section 430.52(C)(1),EX.1, permits you to go up to the next standard size fuses having a rating of 90 amperes.

FLC of motor = 28 amperes [Tbl. 430.248]

28 amperes x 300% = 84 amperes [Tbl. 430.52]

Section 240.6(A) lists the standard ratings of overcurrent devices. Where the ampacity of the conductor does not match a standard overcurrent device as listed in Section 240.6(A), 240.4(B) permits the use of the next larger standard overcurrent device; provided the conductors being protected are not part of a branch circuit supplying more than one receptacle, and where the next higher standard overcurrent device is rated 800 amperes or less.

To calculate the voltage drop on this circuit, first locate the circular mil area of the conductors (10,380 CM) as indicated in Table 8 of Chapter 9. Then apply the single-phase voltage drop formula:

VD = 2 x K x I x D VD = 2 x 12.9 x 20 x 150 = 7.45 volts dropped
CM 10,380

Either may qualify as a grounding electrode. The horizontal or vertical installation of in. diameter steel reinforcing rod or the 4 AWG bare copper conductor within the concrete encasement is required to be in one continuous 20-foot length so that a 20-foot long electrode is in contact with the earth. Reference Section 250.52(3)(1)&(2).

Where the conductors in conduit or tubing are all of the same physical size and insulation characteristic, the use of Annex C tables is permitted. For this question you are to determine the minimum trade size EMT required to enclose eight size 6 AWG THHW conductors. You should have selected a trade size 1 in. EMT from Table C.1 of Annex C.

Section 310.15(B)(5)(a), indicates where a neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be counted as a current-carrying conductor. An example of this would be a 120/240-volt, single-phase, system supplying incandescent luminaires, general-use receptacles and appliances of a residence. Section 310.15(B)(5)(c), mandates on a 3-phase, 4-wire circuit where the major portion of the load consists of nonlinear loads, the neutral conductor is considered a current-carrying conductor. A good example of this type of system is a 208Y/120-volt, 3-phase system that supplies fluorescent luminaires in a school or office building.

The intent of Section 225.4 is to prevent inadvertent contact with the conductors and eliminate a shock hazard.

For the purpose of determining box fill, Table 314.16(B) shows size 12 AWG conductors to be calculated at 2.25 cubic inches per grounded or ungrounded conductor contained in the box. When applying this table, disregard the insulation type and conductor material.

To ensure Type NM cable is adequately supported, Section 334.30 requires the cable to be supported at intervals not exceeding 4 ft.

The general rule is a motor disconnecting means must disconnect both the motor and controller. Refer to Section 430.75(A).

In this situation, Section 240.21(B)(2)(1) requires the ampacity of the tap conductors to be not less than one-third of the rating of the overcurrent device protecting the feeder conductors. Thus, 150 amperes (tap conductors) multiplied by 3 = 450 amperes.

As mandated by Sections 517.33(A)(3)g & (8)f, the critical branch of the hospital essential electrical system shall supply power and task illumination for emergency room treatment areas and nurses stations. The critical branch is intended to serve a limited number of receptacles and locations in order to reduce the load and minimize the chances of a fault condition. The critical branch is intended to automatically connect to alternate power sources by transfer switches during interruption of the normal power source.

Where sizing overcurrent protection for a single non-motor operated appliance, Section 422.11(E) does not address the issue of the length of time the appliance operates. In order to properly size the overcurrent protection for the appliance, you must know the voltage rating and the full-load current of the appliance. Section 422.11(E)(3) permits the overcurrent protection to be sized up to 150% of the full-load current rating of the appliance. Where the overcurrent protection selected does not correspond to a standard ampere rating, the next higher standard rating shall be permitted.

Under this condition, where exposed live parts of equipment having a voltage in excess of 150 volts to ground are on both sides of the working space, Table 110.26(A)(1) requires a working space of 4 ft. between the equipment.

The requirement for listed tamper-resistant 15- and 20-ampere receptacles in child care facilities is intended to increase safety for children. Tamper-resistant receptacles are constructed to prevent one from inserting a metal object such as paper clip into the ungrounded portion of the receptacle. This mandate located in Section 406.12(C) is intended to prevent shock hazards.

Because of the heat transfer from the ballast to the circuit conductors, Section 410.68 requires when the branch circuit conductors are within 3 in. of the ballast, they are to have a temperature rating of not less than 90 C.

The intent of Section 210.19(A)(3) is to ensure the branch-circuit conductors supplying the appliance are large enough to carry the load.

Section 240.4(D)(5) requires overcurrent protection of size 12 AWG conductors to be no more than 20 amperes. The purpose of this mandate is to prevent overloading and overheating of the conductors.

Prior to derating, Table 310.15(B)(16) shows the ampacity of size 2 AWG copper conductors with a 75C temperature rating to be 115 amperes, which is to be multiplied by 0.88 [selected from the temperature correction factors found in Table 310.15(B)(2)(a)]. Therefore the allowable ampacity of the conductor is reduced to 101 amperes.

Size 2 AWG @ 75 deg. C ampacity (before derating) = 115 amperes
115 amperes x .88 (temperature correction factor) = 101 amperes

Because of the heat generated by the heating cables, where conductors are installed less than two inches above a heated ceiling, the ambient temperature surrounding the conductors is considered to be 122F. Reference Section 424.36.

Because of the heat generated by the heating cables, where conductors are installed less than two inches above a heated ceiling, the ambient temperature surrounding the conductors is considered to be 122F. Reference Section 424.36.

When applying the general method of calculation for dwelling units the demand factors specified in Table 220.42 are to be applied. The concept for applying demand factors is that the entire connected load is not likely to be used at one time. To size the service-entrance conductors for a dwelling unit with a connected load of 96,400 VA apply the values as specified in Table 220.42 as shown:

1st 3,000 VA @ 100% = 3,000 VA
remainder (96,400 VA - 3,000 VA) = 93,400 VA @ 35% = 32,690 VA
Demand load = 35,690 VA

In general, circuit breakers with a rating of less than 600 amperes are not listed for continuous-use. This issue is not addressed in the NEC.

In compliance with Section 600.5(B)(2), branch circuits that supply outline lighting systems that are not neon illuminated, shall be rated not to exceed 20 amperes.

This rule is in place to eliminate a shock hazard to patients and health care workers. Reference 517.64(A)(1),(2)&(3).

Section 314.28(A)(1) applies to minimum dimensions of junction boxes used with conduits containing conductors size 4 AWG or larger. In straight pulls the length of the box is required to be not less than eight times the trade size of the largest conduit entering the box. Therefore:

12 in. (box) 8 (raceway) = 1.5 or 1 in. conduit

To determine the voltage drop on this circuit, first find the resistance total with the information given in the question:

Resistance = 4 ohms 1000 ft. = .004 ohms per ft.
.004 ohms x 300 ft. = 1.2 ohms total resistance
Next, apply the voltage drop formula, VD = I X R:
VD= 5 amperes x 1.2 ohms = 6 volts dropped

The requirements of Sections 430.24(1)&(2) are based on the principle that the conductors supplying more than on motor should be sized to have an ampacity equal to 125% of the full-load current of the highest rated motor in the group, plus the full-load currents of all other motors in the group.

10 amps x 100% = 10.0 amperes
20 amps x 100% = 20.0 amperes
30 amps x 125% = 37.5 amperes
TOTAL = 67.5 amperes

As shown in Table 220.12 when calculating the general lighting load of a industrial commercial (loft) building, a unit load of 2 VA per sq. ft. is to be applied. Also as per Section 230.42(A)(1), because this load is considered a continuous load, you are to multiply this value by 125%. First, find the total square feet of the building.

100 ft. x 300 ft. = 30,000 sq. ft. x 2 VA = 60,000 VA
x 125% demand = 75,000 VA

In compliance with Section 210.52(C)(5), receptacle outlets installed for countertop surfaces in dwelling units may be located on or above, but not more than 20 inches above the countertop. The intent of this rule is to eliminate the use of unsightly extension cords (which reduces the amount of usable countertop space) on the countertop to supply cord-and-plug connected appliances. Also, receptacles located more than 20 inches above countertops may interfere with the cabinetry to be installed.

The purpose of this requirement addressed in Section 460.28(A), is to drain off the stored charge in a capacitor after the supply circuit has been opened. Otherwise, a person servicing the equipment could receive a severe shock, or damage could occur to the equipment.

As per Section 440.14, the disconnecting means for an air-conditioning unit is permitted to be installed on the unit, if it is not located on panels that are designed to allow access to the equipment.

Section 250.8(A) recognizes equipment grounding conductors and bonding jumpers are permitted to be connected by exothermic welding, pressure connectors, and machine screw-type fasteners, but sheet metal screws are not an acceptable method of connection.

As mandated in Section 240.51(B), Edison-base type fuses shall be used only for replacements in existing installations. The purpose of this requirement is to phase out the old style fuses.

The purpose of Section 348.30(A) is to ensure flexible metal conduit (FMC) is securely fastened in place.

For emergency systems where internal combustion engines, such as generators, are used as the prime mover, Section 700.12(B)(2) requires a fuel supply sufficient for not less than 2 hours full-demand operation of the system.

To assure Type MI cable is adequately fastened in place, Section 332.30 mandates the cable to be supported at intervals not exceeding 6 ft.

First, find the full-load current available at the generator terminals by using the single-phase current formula and as Section 445.13 requires, multiply this value by 115%.

I = 18 kW x 1000 = 18,000 watts = 75 amperes x 115% = 86 amperes
240 volts 240 volts

Adequately applied overload protection should protect the motor from any overload condition prior to damage occurring in the motor. As per Section 430.32(A)(1), motors with a service factor of less than 1.15 are to have the trip setting of the overload device at no more than 115% of the full-load current rating indicated on the motor nameplate. However, when the overload device selected in accordance with 430.32(A)(1) is not sufficient to start the motor or carry the load, the values shown in Section 430.32(C) are permitted to be used. Where this condition occurs, the trip setting may be 130% of the motor nameplate current rating.

A per Section 250.52(B)(1), a metal underground gas pipe is not approved for use as a grounding electrode.

In compliance with Section 422.11(E)(3), the overcurrent protective device for a non-motor operated appliance is permitted to be sized at 150% of the current rating of the appliance. Where the value selected does not correspond with the rating of a standard size overcurrent device, you are permitted to go up to the next standard size as shown in Section 240.6(A)
.
I = 4,500 watts = 18.75 amperes x 150% = 28.15 amperes
240 volts

Note, the next standard size overcurrent device is rated 30 amperes.

A indicated in Table 310.15(B)(16), size 500 kcmil THWN copper conductors have an allowable ampacity of 380 amperes before any ampacity correction factors are applied. Due to the elevated temperature, multiply 380 amperes by 0.67 [temperature correction value shown in Table 310.15(B)(2)(a)] and due to the number of current-carrying conductors contained in the raceway, multiply by .7 [adjustment factor shown in Table 310.15(B)(3)(a)]. Thus,

500 kcmil THWN copper ampacity before derating = 380 amperes
380 amps x .67 (temp. correction) x .7 (adj. factor) = 178.22 amperes

Section 340.10 recognizes Type UF cable is permitted for use underground, for branch circuits, and in attic spaces, but according to Section 340.12(1) Type UF cable is not allowed for use as service-entrance cable.

Receptacles incorporating an isolated grounding conductor connection, shall be identified by an orange triangle located on the face of the receptacle. Refer to Section 406.3(D).

Section 250.106 specifies that the grounding electrode system of the lightning protection system be bonded to the electrical service grounding electrode system.

Article 100, where definitions are found, reveals a ground-fault circuit interrupter is a device intended for the protection of personnel that functions to de-energize a circuit when a ground-fault occurs

As per Section 324.10(B)(2), individual branch circuits of FCC systems shall have ratings not to exceed 30 amperes.

As defined in Article 100, the system bonding jumper is the connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system. This connection is permitted either at the source of the separately derived system or at the first disconnecting means supplied by the source.

In compliance with Section 555.22, facilities for the repair of marine craft that contain flammable liquids or gases must also comply with the requirements mandated in Article 511. As per Section 511.3(C)(1)(b), receptacle outlets located 16 inches above the floor in an unvented vehicle repair shop containing flammable liquids, are considered to be installed in a Class I, Division 2 location.

As indicated in Section 110.6, conductor sizes are expressed in American Wire gage (AWG) or in circular mils.

Table 300.19(A) shows where a vertical raceways contains size 3/0 AWG copper conductors, they are to be supported at intervals not greater than 80 feet. This requirement prevents the weight of the conductors from damaging the insulation where they leave the conduit and prevents the conductors from being pulled out of the termination lugs.

To ensure an adequate grounding system and qualify as an effective grounding electrode, according to Section 250.53(G), all rod and pipe electrodes have at least 8 ft. of length in contact with the soil.

Section 110.14(C) states the temperature rating associated with the ampacity of a conductor shall be selected so as not to exceed the temperature of any connected terminal. But, for conductors with a temperature rating with a higher value than that of the terminations, the higher value can be used for ampacity adjustment and correction. Prior to derating, Table 310.15(B)(16) shows size 3 AWG THHN copper conductors to have an ampacity of 115 amperes, which is to be multiplied by 0.96, due to the ambient temperature [selected from Table 310.15(B)(2)(a), where the temperature factors are shown]. Therefore the allowable ampacity is reduced to 110.4 amperes. However, since the terminations are rated for 60C, the ampacity of the conductor is to be selected from the 60C column, which shows the allowable ampacity to be 85 amperes.

3 AWG THHN ampacity before derating = 115 amperes (90 deg. C Col.)
115 amperes x .96 (temperature correction) = 110.4 amperes.
3 AWG (60 deg. C Col.) = 85 amperes is to be used.

The general rule is, in order to prevent accidental contact and damage to communications wires and cables, as explained in Section 800.44(B), they are to have a vertical clearance of not less than 8 ft. from all points above roofs.

To ensure PVC conduit is secured and fastened in a stable and workmanlike manner, Table 352.30 indicates 2 in. Schedule 40 PVC is required to be supported at least every 5 ft.

In compliance with Section 450.21(B), where located indoors, individual dry-type transformers of more than 112 kVA rating are to be installed in a transformer room of fire-resistant construction having a rating of not less than 1 hour. This requirement provides a confinement area and a degree of protection in the event of a fire or an accident.

Section 300.20(A) addresses the problem of induction from ac conductors into ferrous (magnetic) metal enclosures and raceways. To prevent induced current where conductors are installed in ferrous metal raceways, all phase conductors, the grounded conductors and equipment grounding conductors should be grouped together. Induction into raceways and enclosures can lead to conductors overheating and creating a shock hazard.

To minimize the length of unsightly cords, Section 440.64, mandates the maximum length permitted for a flexible cord supplying a 208-volt, single-phase, room air-conditioner to be 6 ft.

Under this condition, Sections 240.21(B)(4)(2)&(9), permits a tap of 100 ft. for manufacturing buildings where the tap connection is made not less than 30 ft. from the floor and conditions of maintenance ensure that only qualified persons service these systems.

As addressed in Section 250.64(E), ferrous metal enclosures that are not physically continuous from cabinets or equipment to the grounding electrode shall be made electrically continuous by bonding each end of the raceway or enclosure to the grounding electrode conductor. Bonding at both ends of the raceway ensures that the raceway and conductor are in parallel. These bonding connections are necessary so that the ferrous metal raceway does not create an inductive choke on the grounding electrode conductor.

The intent of Section 300.13(B) is to permit the replacement of a receptacle without interrupting the continuity of the downstream grounded (neutral) conductor. Opening the neutral could cause unbalanced voltages and a higher voltage would be impressed on one part of a multiwire branch circuit. Also, when replacing a receptacle, this requirement helps to prevent personnel from becoming in series with the neutral conductor, which creates a shock hazard.

According to Section 210.8(A)(2), all single-phase, 125-volt, 15- or 20-ampere receptacles located in residential garages are required to be provided with ground-fault protection for personnel. This requirement improves safety for persons using portable handheld portable tools and similar tools that might be connected to these receptacles. GFCI protection is also required because auto repair work and maintenance is performed and workshop electrical tools are often used in the garage. There are no exceptions to this rule, regardless of where in the garage the receptacle is located or the equipment served. Most safety experts agree that GFCIs are directly responsible for saving numerous lives and preventing countless injuries. Section 210.12(A) lists the areas of a dwelling unit where all 120-volt, single phase, 15- and 20-ampere branch-circuits supplying outlets and devices are mandated to have AFCI protection. Residential garages are not are not included in this list. However, AFCI devices may also be capable of performing other functions such as overcurrent protection, ground-fault protection and surge suppression. Therefore, AFCI devices are certainly permitted to be installed in residential garages, but not required.

To solve this problem, first determine the VA of the transformer, then divide by 1000 to determine the kVA.

208 volts x 1.732 x 243 amperes = 87,542 VA

87,542 VA = 87.5 kVA
1000

Section 200.4(A) specifies that an individual neutral conductor be provided for each two-wire and multiwire branch circuit and feeder unless specifically permitted elsewhere in the NEC. The concern with multiple circuits sharing a common neutral conductor is the possibility of overloading the neutral conductor. Typically, the neutral conductor is not provided with overload protection therefore, when the neutral conductor is overloaded the conductor insulation can be damaged. Specific provisions covered in Sections 215.4 and 225.7 do permit multiple circuits to have a common or shared neutral conductor.

The size of the grounding electrode conductor at an ac service is based on the size of the largest service-entrance conductor or equivalent area for parallel conductors as shown in Table 250.66. Therefore, size 500 kcmil aluminum x 4 conductors = 2000 kcmil total

*NOTE- Aluminum service-entrance conductors over 1750 kcmil require a size 3/0 AWG copper grounding electrode conductor.

The loads on transformer arc welders are considered intermittent. Therefore, the minimum ampacity of the branch-circuit conductors is permitted to be determined by applying the percentage values shown in Table 630.11(A). This calculation is done by selecting the appropriate factor from the table, based on the duty cycle and type of welder, then multiply by the value of the welder rated primary current. The conductors are to be selected from Table 310.15(B)(16).

.78 (duty cycle factor) x 50 amperes (primary current) = 39 amperes
Table 310.15(B)(16) requires size 8 AWG 60C rated conductors.

In order to protect cables or raceways from mechanical damage from the penetration of nails and screws, the general rule of Section 300.4(A)(2) specifies where laid in notches of wood studs, the cable or raceways must be protected by a steel plate at least 1/16 in. thick.

To discourage the use of floor receptacles and unsightly extension cords likely to be damaged due to personnel tripping and walking on them, Section 210.62 requires receptacle outlets provided for show window lighting to be located within 18 in. of the top of the show window.

A grounding electrode system has been required to be established for PV systems and PV arrays since the 1996 edition of the NEC. Section 690.47(D) makes it clear that ground, pole-mounted and roof-mounted PV arrays require an auxiliary grounding electrode system. The large quantity of conductive material that is added to a roof when a PV system is installed increases the likelihood of a lightning strike. This PV grounding electrode system would help to minimize the effects of such a lightning strike. The primary purpose of this PV grounding electrode is to maintain the frames of the PV array as close to local earth potential as possible. Another purpose of this PV grounding electrode system is to provide a simple and direct path for any static charge that may build up during a storm or lightning strike. At this time, the NEC does not address the issue of the need of a general-use receptacle to be located in close proximity to photovoltaic arrays.

Table 5 of Chapter 9 shows the various sizes and insulation of conductors expressed in millimeters and square inches in accordance with appropriate diameter and square inches. In most cases we relate to the approximate area in sq. in. on the right side of the table. This calculation is done by locating the sq. in. value of each conductor and multiply by the number of conductors. Next, add the values together as shown:

4/0 AWG THWN - .3237 sq. in. x 3 = .9711 sq. in.
3/0 AWG THWN - .2679 sq. in. x 1 = .2679 sq. in.
4 AWG THWN - .0824 sq. in. x 1 = .0824 sq. in.
TOTAL 1.3214 sq. in.

Due to the close proximity of the conduit to the rooftop, first find the temperature adder, 40 F, as shown in Table 310.15(B)(3)(c). Then, add this value to the ambient temperature.

110F (ambient temperature)
+40F (adder)
150F (to be used for derating)

Next, locate the temperature correction factor to be applied, 0.33, from Table 310.15(B)(2)(a). Finally, multiply 0.33 x 65 amperes, the allowable ampacity of size 6 AWG THWN copper conductors before derating, as indicated in Table 310.15(B)(16).

Size 6 AWG THWN ampacity (before derating) = 65 amperes
65 amperes x .33 (temperature correction) = 21.45 amperes

As per Section 430.110(A), the disconnecting means for motor circuits rated 1000 volts or less, shall have an ampacity of at least 115% of the full-load current rating of the motor.

The general rule for feeder conductors of not more 600 volts, supplying continuous loads is, the conductors are to have an ampacity of not less than 125% of the full-load current of the load to be served. Reference Section 215.2(A)(1)(a).

Section 220.12 requires a unit load of not less than that specified in Table 220.12 is to be used for determining the minimum general lighting load.

Multiply this value by the sq. ft. of the occupancy.
12,000 sq. ft. x 2 VA = 24,000 VA (building lighting VA)

Next, find the VA of one circuit by multiplying volts x amperes.
120 volts x 20 amperes = 2,400 VA (one circuit VA)

Finally, divide the load, 24,000 VA, by one circuit, 2,400 VA.
24,000 VA (blg.) 2,400 VA (one circuit) = 10 general lighting circuits

To determine the voltage drop on this circuit, first locate the circular mil area 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 80 amps x 200 ft. = 7.84 volts
CM 52,620 CM

Where installed in Class I, Division 1 locations, Section 501.15(A)(1) requires conduit seals to be installed within 18 in. of enclosures containing components that have arcing devices. This requirement for the location of conduit seals is to prevent an explosion from traveling through the conduit and to minimize the passage of gasses or vapors from hazardous locations to nonhazardous locations.

In accordance with Section 700.12(F)(2)(3), the branch circuit feeding the unit equipment shall be the same branch circuit as that serving the normal lighting in the area and connected ahead of any local switches. Unit equipment is intended to provide illumination for the area where it is installed. For instance, if an emergency lighting unit is located in the hallway of a school building, it must be unswitched and connected to the branch circuit supplying the normal hallway lights. Unit equipment is designed to automatically energize the unit luminaire lamps, restoring illumination to the hallway in the event of normal power failure.

Both Table 514.3(B)(1) and Figure 514.3 recognize an area of 20 ft. around outdoor motor fuel dispensers to be a hazardous location.

Where a grounding electrode conductor is connected to a ground rod, or where two or more ground rods are bonded together, Section 250.66(A) permits the conductor to be sized at not larger than 6 AWG copper.

Refer to Section 230.79(C) and find the service disconnecting means for a for a dwelling is to have a rating of not less than 100 amperes.

To solve this problem, apply the 3-phase current formula:
I = Power
Volts x 1.732

I = 90 kVA x 1000 = 90,000 VA = 250 amperes
208 volts x 1.732 360.25

First, locate the full-load current of the motor, 27 amperes, from Table 430.250 next, multiply by 115%, as per Section 430.110(A).
FLC of motor = 27 amperes x 115% = 31.05 amperes

In compliance with Section 392.10(B)(1)(a), ungrounded single-conductor cable installed in cable trays shall be 1/0 AWG or larger.

As covered in Section 700.12, an approved supply system for legally required standby purposes, in addition to the normal services to the building, may be a storage battery back-up system. Section 700.12(A) requires a storage battery to have a suitable rating and capacity to supply and maintain not less than 87 percent of system voltage the total load of the circuits supplying legally required standby power for a period of not less than 1 hours. Legally required systems are intended to provide electric power to municipal first responders such as fire stations, sheriff offices, highway departments, police stations and similar operations to aid in fire fighting, emergency situations, rescue operations and control of health hazards. When normal power is lost, legally required systems must be able to supply standby power in 60 seconds or less.

Section 230.3 prohibits service conductors supplying a building from passing through the interior of another building. Although service conductors that supply one building are prohibited from being run through the interior of another building, service conductors are permitted to be installed along the exterior of a building to supply another building.

According to Section 430.36, where fuses are used for motor overload protection, all 3-phase motors must be provided with 3 overload units, one in each phase.

In compliance with Section 215.2(A)(1)(a), feeder conductors are to have an ampacity of 100% of the continuous loads, plus 125% of the continuous loads. Therefore:

18,000 VA x 100% = 18,000 VA
13,356 VA x 125% = 16,695 VA
34,695 VA total

To find the load, apply the single-phase current formula:

I = 34,695 VA = 144 amperes
240 volts

As shown in Table 310.15(B)(16), size 1/0 AWG conductors with an allowable ampacity of 150 amperes should be selected.

As permitted by Section 450.13(B), transformers rated 1000 volts or less and not exceeding 50 kVA may be installed in hollow spaces of hung ceiling areas, provided these spaces are fire resistant, ventilated and accessible.

Section 250.148(C), mandates a grounding screw shall be used for no other purpose than connecting the equipment grounding conductor.

When considering these conditions, Column 4 of Table 300.5, indicates the minimum burial depth of the Type UF cable to be 12 inches.

Section 320.10(1) recognizes Type AC cable is permitted for use as feeders. But, Sections 320.12(1)&(2) do not permit Type AC cable to be used in damp or wet locations and where subject to physical damage.

The carpet squares covering Type FCC cable are not permitted to be larger than 39.37 inches (1.0 m) square, to comply with Section 324.41. This limitation provides ready access to the cable by lifting a carpet square. It also reduces the likelihood of damage to the cable by personnel cutting through the carpet above the cable and penetrating the top shield of the cable. Type FCC (flat conductor cable) is a wiring system currently in use in many offices. Type FCC is prohibited for use in residential, school and hospital buildings.

The intent of Section 300.4(A)(1) is to prevent nails and screws from being driven into the cables when installing the wallboard. Where the NM cable is installed through bored holes in wood studs where the edge of the hole is not less than 1 in. from the nearest edge of the wood member, the likelihood of the cable being damaged due to the penetration of nails and screws is greatly reduced.

The purpose of the 18 inch submergence requirement for luminaires, as addressed in Section 680.23(A)(5), is to reduce the likelihood that a person in the water and hanging onto the side of the pool directly in front of the luminaire will have his or her chest in line with the luminaire. The highest level of leakage current in a pool coming from a wet-niche luminaire with a broken lens and bulb is found directly in front of the luminaire. This rule helps to reduce the possibility of a shock hazard occurring.