The requirement indicated in Section 690.11 is limited to PV systems with a
maximum voltage of 80 volts or greater. PV systems can be subjected to extreme
environmental conditions such as, wind, rain, snow, ice, and elevated temperature
extremes. These systems can deteriorate over time and eventually develop
insulation failures or internal PV module conductor fault conditions. The AFCI device
is provided to interrupt arcing faults resulting from a failure in the intended
continuity of a conductor, connection, module, or other system component in the dc
PV circuits.

Section 314.20 applies only to the construction of the surface of the wall or ceiling
and not to its structure or subsurface. Therefore, a wall constructed of wood but
sheathed with an outer layer of gypsum board is permitted to contain boxes set back
or recessed not more than in. Using an opposite example, a wall constructed of
metal studs but finished with wood panels requires that the outlet boxes be mounted
flush with the combustible material.

In compliance with Section 517.19(D), each patient care vicinity in a critical care
area of a hospital is permitted to have a patient equipment grounding point. An
equipment bonding jumper not smaller than 10 AWG shall be used to connect the
grounding terminal of all grounding-type receptacles to the patient equipment
grounding point.

The intent of Section 645.5(A) is to recognize that information technology
equipment can operate for over 3 hours, therefore it is to be considered a
continuous load and the branch-circuit conductors supplying the equipment are to
have an ampacity not less than 125% of the total connected load.

Section 680.43(B)(1)(b) permits GFCI protected luminaires over indoor installed hot
tubs to be installed at a minimum height of 7 ft. The intent of this rule is to
protect persons from an electrical shock hazard.

Where a motor has a temperature rise of 50C marked on the nameplate, for the
purpose of selecting the overload device, Section 430.32(A)(1) requires this device
shall be selected to trip at not more than 115% of the motor nameplate full-load
current rating. Motors are required to be protected from overloads and the basic
premise of this rule is that the operation of a motor in excess of its normal full-load
rating for a prolonged period of time causes damage or dangerous overheating that
may start a fire. Overload protection is intended to protect the motor and the
system components from damaging overload currents.

Table 300.5 indicates all wiring methods installed under airport runways and
adjacent areas to be placed at a depth of not less than 18 in. This required depth
reduces the risk of damaging the conductors and raceways that may be caused by
heavy aircraft traffic.

Section 250.118(6)d permits liquidtight flexible metal conduit (LFMC) for use as an
equipment grounding conductor if it does not exceed 6 feet in length. However,
when LFMC is used to connect equipment where flexibility is necessary due to the
anticipated movement of the equipment after installation, Section 250.118(6)e
mandates an equipment grounding conductor to be installed regardless of the length
of the LFMC.

Overcurrent protection devices are not permitted to be located in bathrooms of
dwelling units and guest rooms of hotel and motels. Reference Section 240.24(E).

In compliance with Section 430.22(E), for motors that are not continuous duty, the
motor nameplate currents and Table 430.22(E) are used to determine the branch-
circuit ampacity. Table 430.22(E) shows the duty-cycle service for a 15 minute,
short-time duty motor and indicates the nameplate current rating of 25 amperes is
to multiplied by 120% to determine the ampacity of the conductors.

FLC of motor = 25 amperes x 120% = 30 amperes

Size 10 AWG THWN copper conductors with an allowable ampacity of 35
amperes should be selected from Table 310.15(B)(16).

Section 400.31(A) applies to multiconductor portable cables, over 600 volts, used to
connect mobile equipment and machinery. The conductors shall be 12 AWG or larger
and shall employ flexible stranding.

To comply with the rules specified in Section 430.6(A)(1), for single-phase, general
motor applications, the ampere rating of the overcurrent protective devices are to
be based on the ampere values expressed in Table 430.248. This table shows the
motor to have a full-load running current of 24 amperes. Table 430.52 indicates
where nontime delay fuses are used to protect a single-phase motor they are to
have a rating of not more than 300% of the motor FLC.

FLC of motor - 24 amperes x 300% = 72 amperes

In this situation where exceptions are not applied, you must go down to the next
standard size nontime-delay fuse with an ampere rating of 70 amperes. [240.6(A)]

Where used as both controller and disconnecting means for a motor, Sections 430.111(B)(1),(2)&(3) recognizes the permitted use of an oil switch, an air-break switch, and an inverse time circuit breaker, but the use of an instantaneous-trip
circuit breaker is not permitted. It is the intent of Section 430.111 to permit
omission of an additional device to serve as a disconnecting means.

As mandated by Section 501.100(A)(1), where transformers containing oil or a
liquid that will burn are located in a Class I, Division 1 location, they shall be
installed in vaults only. The purpose of this rule is to prevent the spread of burning
oil to other combustible materials in the event of a fire or an explosion.

Section 310.15(B)(3)(2) states adjustment factors shall not apply to conductors in
raceways having a length not exceeding 24 in. This section recognizes where
conductors are installed in short sections of raceways of not over 24 inches in
length, the heating effect caused by the number of current-carrying conductors in
the raceway is very little and the reduction of the ampacity of the conductors is
insignificant.

When installing conductors of different sizes in junction boxes, the total box volume
required is determined by adding the individual volumes of the box components. Section 314.16 provides the requirements, and identifies the allowances for the number of conductors permitted to be housed within a box. Table 314.16(B) shows
the volume, in cubic inches of the individual conductors. Each ungrounded or grounded conductor that enters the box and terminates or spliced within the box shall be counted once. [314.16(B)(1)] Internal box clamps are to be counted as one conductor, based on the largest conductor present in the box. [314.16(B)(2)] Equipment grounding conductors, one or more, are counted as one conductor, based on the largest equipment grounding conductor present in the box. [314.16(B)(5)]

Size 6 AWG ungrounded conductors - 3 x 5.00 cu. in. = 15.00 cu. in.
Size 6 AWG grounded conductors - 3 x 5.00 cu. in. = 15.00 cu. in.
Size 8 AWG grounding conductor - 1 x 3.00 cu. in. = 3.00 cu. in.
Size 12 AWG ungrounded conductors - 3 x 2.25 cu. in. = 6.75 cu. in.
Size 12 AWG grounded conductors - 3 x 2.25 cu. in. = 6.75 cu. in.
Size 12 AWG grounding conductor - -0-
internal clamps - 1 x 5.00 cu. in. = 5.00 cu. in.
TOTAL = 51.50 cu. in.

Section 770.26 requires openings around penetrations of optical fiber cables and
communications raceways through fire-resistant-rated partitions to be firestopped
using approved methods. This rule is in place so that the possible spread of fire will
not be increased if a fire occurs.

Table 680.8(A) and Figure 680.8(A) illustrate where service-drop conductors and
open overhead wiring from 0-750 volts cross above a swimming pool, a clearance
of not less than 22 ft. must be maintained from the base of the diving board and
the conductors. The intent of these clearances is to prevent inadvertent contact
with the conductors when using skimmers with aluminum handles when cleaning
the pool.

The purpose of Section 517.32(H) is to provide an automatic means of egress from
a health care facility in the event of an emergency.

The general requirement of Section 230.2 is that a building shall be supplied by only
one service. However, Section 230.2(A)(1) permits an additional service to be
provided to supply fire pumps. The concept of this rule is to maintain fire protection
upon interruption of the normal service.

In order to prevent the potential for personnel making inadvertent contact with
service-drop conductors, Section 230.24(A) requires a vertical clearance of not less
than 8 ft. be maintained from the conductors to the roof surface.

Section 408.3(E)(1) addresses the phase arrangement of 3-phase buses of ac
panelboards and switchboards. The phase arrangement on 3-phase busses shall be
A, B, C, from front to back, top to bottom, or left to right as viewed from the front of
the switchboard or panelboard. The purpose of the rule is to standardize the phase
arrangement of 3-phase ac equipment used in the electrical industry.

The intent of Section 210.52(E)(3) is to provide a receptacle on the porch or deck of
dwellings so that the occupants have access to electrical power without the need of
extension cords passing through doorways, which may cause a tripping or electrical
hazard.

Section 695.14(E) permits liquidtight flexible metal conduit (LFMC), liquidtight
flexible nonmetallic conduit (LFNC) and intermediate metal conduit (IMC) to be used
as wiring methods for use of enclosing control wiring for electric motor-driven fire
pumps. Flexible metal conduit (FMC) is not approved for such use.

As covered in Section 110.26(E)(1)(a), the dedicated electrical space is required to
be clear of piping, ducts, leak protection apparatus, or equipment foreign to the
electrical installation. Plumbing, heating, ventilation and air-conditioning ducts must
not be located in this dedicated electrical space. Associated electrical equipment
such as busways, raceways, conduits and cables are permitted to enter equipment
through this zone.

Section 250.66(A) permits that portion of a grounding electrode conductor that is
the sole connection to a made grounding electrode such as a driven ground rod, pipe
or buried plate, to be not larger than 6 AWG copper.

The Informational Note of Section 690.42, indicates locating the grounding
connection point as close as practicable to the photovoltaic source better protects
the system from voltage surges due to lightning.

As per Section 310.10(H)(1), phase conductors, neutral, or grounded conductors
shall be permitted to be connected in parallel only in sizes 1/0 AWG or larger.

Section 455.2 defines a phase converter as an electrical device that converts single-
phase power to 3-phase power. Phase converters are commonly used to supply 3-phase motor loads in locations
where only single-phase power is available from the local utility. Electrical
installations on farms and in other rural areas are examples of such locations.

Section 300.22(B) applies to sheet metal ducts and other ducts specifically
constructed to transport environmental air. The rules in this section limits the use of
materials that would contribute smoke and products of combustion during a fire in an
area that handles environmental air. This section lists the wiring methods permitted
to be installed in environmental air ducts. The question had only electrical metallic
tubing (EMT) approved for such use.

For general motor applications, separate motor overload protection is to be based
on the motor nameplate current rating and not on the full-load running current
value as given in the NEC tables. In compliance with Section 430.32(A)(1), the
overload device shall be selected to trip or shall be rated at no than 115% of the
motor nameplate full-load current rating where the motor has a temperature rise
greater than 40C.

Nameplate ampere rating of motor = 26 amperes x 115% = 29.9 amperes

As specified in Section 502.130(A)(3), in Class II, Division 1 locations, where rigid
metal conduit (RMC) supports pendant suspended luminaires and a means of
flexibility is not provided, the RMC shall have a length of not more than 12 inches.

It is permissible to calculate the demand load for related commercial cooking
equipment in accordance with Table 220.56. Commercial electric cooking
appliances are sometimes used continuously from morning until night, therefore the
demand factors for commercial applications are not as generous as those permitted
for dwelling units.

14.00 kW - range
5.00 kW - water heater
0.75 kW - mixer
2.50 kW - dishwasher
2.00 kW - booster heater
2.00 kW - broiler
26.25 kW - total connected load x 65% = 17.06 kW

*NOTE - However, Section 220.56 states the demand shall not be less than the two
largest pieces of equipment. 14.00 kW + 5.00 kW = 19 kW demand

The condition specified in Section 511.3(D)(3)(b) applies to facilities that primarily
do oil and filter changes and lubrication-type services, not the transfer of fuel.
Where the pit below floor level is not provided with ventilation, this below-grade
work area is classified as a Class I, Division 2 location.

Table 110.28 indicates where a motor controller is located outdoors and is exposed
to sleet, it shall have a minimum rating of 3S, where the controller mechanism is
required to be operable when ice covered. This enclosure selection table is in place
to ensure installers select the proper enclosure that provides a degree of protection
against specific environmental conditions.

Due to the amount of heavy vehicle traffic across a commercial driveway or parking
lot, Table 300.5 specifies the minimum cover requirements to be 24 in. regardless of
the type of wiring method used.

The fumes given off by some storage batteries are very corrosive and can produce
an explosive mixture. To prevent this from happening, Section 480.9(A), requires
ventilation of a battery room to prevent the accumulation of an explosive mixture.
The ventilation method is not necessary to be mechanical.
Hydrogen disperses rapidly and requires little air movement to prevent
accumulation. Since hydrogen is lighter than air and tends to concentrate at ceiling
level, a form of ventilation should be provided near the ceiling level. Ventilation
methods may be a fan, roof ridge vent, or louvered area.

As permitted by Exception No. 1 to the mandates covered in Section 430.52(C)(3),
for other than Design B energy-efficient motors, where the setting specified in Table 430.52 is not sufficient for the starting current of the motor, the setting of an instantaneous trip circuit breaker may be permitted to be increased at a value not to
exceed 1300% of the motor full-load current.

As per Section 450.3(B), to determine the overcurrent protection required for a
transformer of less than 600 volts, the protection shall be provided in accordance
with Table 450.3(B). First determine the full-load current rating of the transformer
by applying the 3-phase current formula, then multiply by the values shown in Table 450.3(B). (Primary)

I = VA I = 150,000 = 150,000 = 180 amps x 250% = 450 amperes
E x 1.732 480 x 1.732 831.36

(Secondary)

I = VA I = 150,000 = 150,000 = 416 amps x 125% = 520 amperes
E x 1.732 208 x 1.732 36.25

Since this full-load current value does not correspond to a standard size overcurrent
device, and it is permitted to go up to the next standard size, a 600 ampere rated
overcurrent protective device is permitted.

The intent of Section 322.10(3) is to protect the flat cable assembly from physical
damage.

In compliance with the motor rules specified in Section 430.6(A)(1), for 3-phase,
general motor applications, the ampere rating of the overcurrent protective devices
are to be based on the motor full-load running current value given in Table 430.250. The table shows the motor to have a full-load current rating of 21 amperes. The actual rating or setting of the overcurrent protection devices are to
be sized in accordance with Table 430.52.

FLC of motor = 21 amperes x 150% = 31.50 amperes

In this question exceptions are not to be applied, therefore you are required to go
down to the next standard size fuses, indicated in Section 240.6(A), having a rating
of 30 amperes.

The intent of Section 300.3(C)(1) is to make it clear that the maximum circuit
voltage in the raceway, not the maximum insulation voltage rating of the
conductors, is what determines the minimum voltage rating required for the
insulation of conductors for systems of 1000 volts or less.

Prior to derating, Table 310.15(B)(16) shows the ampacity of size 2 AWG THWN
copper conductors to be 115 amperes, which is multiplied by 0.8 [selected from the
adjustment factors found in Table 310.15(B)(3)(a)]. Therefore, the allowable
ampacity of the conductors is reduced to 92 amperes.

115 amperes x .8 = 92 amperes

To solve this problem, take into consideration the following:

1) As per Article 100, lighting circuits for a commercial building such as a bank
are considered continuous loads.
2) In compliance with Section 210.19(A)(1), branch-circuits must have an allowable
ampacity of not less than 125% of the continuous loads to be served.
3) General-use receptacles are not considered continuous loads.
4) Electric signs are to be on a separate dedicated circuit. Section 600.5(A)
5) Minimum lighting loads are to be calculated in accordance with the values
given on Table 220.12.
6) As per Section 220.14(K)(2), when the number of receptacles to be installed is
unknown, an additional one (1) VA per sq. ft. is to be added to the general-
lighting load.
Therefore, do the math as shown to determine the minimum number of 120-volt,
20-ampere branch circuits required for this building.

6,000 sq. ft. x 3.5 VA = 21,000 VA x 125% = 26,250 VA (lighting)
6,000 sq. ft. x 1.0 VA = 6,000 VA (receptacles)
32,250 VA (receptacles & lighting)

120 volts x 20 amperes = 2,400 VA of one circuit
32,250 VA (load) 2,400 VA (one circuit) = 13.4 circuits = 14 circuits
14 circuits (lighting & receptacles) + 1 sign circuit = 15 circuits total

The intent of Section 320.30(B) is to ensure Type AC cable is adequately supported
where installed on or across framing members.

To determine the allowable ampacity of the conductors required from the terminals
of the generator to the first overcurrent device, first apply the 3-phase current
formula to find the full-load current rating of the generator:

I = kW x 1,000 I = 200 x 1,000 = 200,000 = 240.56 amperes (FLC)
volts x 1.732 480 x 1.732 831.36

Next, as per Section 445.13, multiply by 115%:

241 amperes x 115% = 277 amperes (required ampacity of conductors)

Finally, size 300 kcmil THWN conductors with an allowable ampacity of 285 amperes
should be selected from Table 310.15(B)(16).

Section 551.78(A) requires all switches and circuit breakers located in wet locations
of a RV park to be weatherproof. This rule is to ensure the equipment is sufficiently
protected when exposed to weather conditions and water.

To determine the minimum number of 15-ampere, 120-volt general lighting circuits
required for the dwelling, refer to Section 220.12 and note that open porches and
garages are not to be included in the calculation. A unit load not less than specified
in Table 220.12 shall constitute the minimum lighting load.

First, determine the usable square feet of the building and multiply by 3 VA as
shown in Table 220.12:

1,400 sq. ft. + 1,400 sq. ft. = 2,800 sq. ft. x 3 VA = 8,400 VA

Next, find the VA of one circuit by multiplying 120 volts by 15 amperes:

120 volts x 15 amperes = 1,800 VA of one circuit

Then, divide the lighting load (8,400 VA) by the VA of one circuit (1,800 VA):

8,400 VA (load) = 4.6 = 5 circuits total
1800 VA (one circuit)

For the purpose of determining box size and permitted fill, Table 314.16(B) shows
the volume allowance, in cubic inches, required per conductor from sizes 18 AWG to
6 AWG. However, when sizing pull and junction boxes housing conductors of size 4
AWG and larger, the required box dimension is to be calculated based on the
diameter of the raceways entering and exiting the enclosure and the rules covered
by Section 314.28 are to be applied.

Section 314.21 requires noncombustible surfaces that are damaged around boxes to
be repaired so there will be no gaps greater than 1/8 in. around the box.

A listed Type IC recessed luminaire is provided with thermal protection to deactivate
the lamp should the luminaire be mislamped so that it overheats. Unless a
recessed luminaire is listed as Type IC, Section 410.116(B) requires thermal
insulation to not be installed above a recessed luminaire or within 3 in. of the
recessed luminaire's enclosure, wiring compartment, ballast, transformer, LED driver
or power supply.

The intent of the rules set forth by Section 110.31 is to ensure enclosures housing
electrical equipment over 600 volts is accessible to qualified persons only and to
deter persons that are not qualified. Therefore, where a fence is used to enclose an
outdoor installation of 2,400 volt electrical equipment, the fence is required to be
not less than 7 ft. in height.

Section 250.178 requires the minimum size copper equipment grounding conductor
required for grounding secondary circuits of an instrument transformer, such as a
current transformer, to be 12 AWG.

As mandated by Section 700.12(A), storage batteries used as a source of power for
emergency systems shall be of a suitable rating and capacity to maintain the total
load for at least 1 hours, without the voltage applied to the load falling below 87
percent of normal.

Because of the need to provide a sufficient number of general-use receptacles for
the cord-and-plug connected appliances in dwelling units, those receptacle outlets
installed in floors more than 18 in. from the wall, are not to be counted as part of
the required number of receptacle outlets. Refer to Section 210.52(A)(3).

In compliance with Section 220.84(C)(3), when using the optional method of
calculation for multifamily dwellings, the nameplate ratings of the appliances are to
be used and the demand factors of Table 220.84 apply.

8 kW x 32 units x .31 (demand factor) = 79.36 kW

Ground-fault protection of services is designed to provide protection from line-to-
ground-faults that occur on the load side of the service disconnecting means. The
requirements of Section 230.95(A) place a restriction on ground fault currents
greater than 3,000 amperes and limits the duration of the fault to be not more than
1 second. This time restriction limits the amount of damage done by an arcing fault,
which is directly proportional to the time the arcing fault is allowed to burn.

To ensure the effectiveness of a grounding electrode plate, each grounding
electrode plate shall expose not less than 2 sq. ft. of surface to exterior soil.
Refer to Section 250.52(A)(7).

The warning ribbon required in Section 300.5(D)(3) is to be placed in the trench at
least 12 inches above the underground installation. This requirement reduces the
risk of an accident, an electrocution, or an arc-flash incident during excavation near
underground service conductors that are not encased in concrete.

Section 430.6(A)(1) indicates to size the overcurrent protection for a 3-phase 50
hp, 480-volt, motor used in a general application, the full-load running current
value, 65 amperes, shown on Table 430.250 shall be used. For 3-phase motors,
Table 430.52 requires the rating of time-delay fuses to be no more than 175% of
the FLC of the motor.

FLC of motor - 65 amperes x 175% = 113.75 amperes

Since exceptions were not applicable on this question, you should have selected
fuses with a standard rating of 110 amperes from Section 240.6(A).

Where installed indoors, to reduce the risk of a fire, dry-type transformers having a
rating of 112 kVA or less are to have a separation of at least 12 in. from
combustible material. Refer to Section 450.21(A).

Section 220.43(B) is meant to be used for load calculations. This section requires a
load of 150 VA is to be used for every two (2) feet of lighting track or fraction
thereof.

As per Section 515.7(A), where PVC conduit is used as a fixed wiring method above
bulk fuel storage tanks, the PVC shall be Schedule 80 PVC conduit.

The requirement of Section 220.14(H)(2) states that where appliances are likely to
be used simultaneously, each foot of multioutlet assembly is to be considered as
one outlet rated 180 volt-amperes.

In order to provide adequate protection of underfloor raceways, Section 390.4(A)
requires 4 in. wide raceways to have a covering of wood or concrete not less than
3/4 in. above the raceway.

Where aerial service-drop conductors of not over 600 volts cross above an orchard
they are required to have a vertical clearance of not less 18 ft. from final grade.
The intent of the requirements listed in Section 230.24(B)(4) is to protect the
conductors from physical damage and to protect persons from accidental contact
with the conductors.

As per Section 680.42, the rules that govern outdoor installations for a spa or hot
tub shall comply with the provisions that cover permanently installed swimming
pools. In compliance with Section 680.22(A)(1), where a spa or hot tub is installed
at a dwelling unit, at least one (1) 125-volt, 15- or 20-ampere receptacle is to be
located not more than 20 ft. from the inside wall of the spa or hot tub. The intent of
this requirement is to permit ordinary appliances to be safely plugged in and used
near the spa or hot tub but to avoid the need for extension cords in the vicinity of
the spa or hot tub.

Section 680.21(A)(5) permits pool-associated motors to be cord-and-plug
connected. The flexible cord shall not exceed 3 ft. in length. This wiring method is
permitted due to the vibration of the motors and flexibility is required.

In general, Section 404.8(A) requires the maximum height above the floor or
working platform to the center of the operating handle of a switch when it is in the
ON position must not exceed 6 ft. 7 in.

Due to the presence of gaseous vapors, Table 514.3(B)(1) indicates the upward
discharging vent of an underground fuel tank of motor fuel dispensing facilities is a
Class I, Division 1 location within 5 feet of the open end of the vent.

Unlike flexible metal conduit (FMC) or liquidtight flexible metal conduit (LFMC),
as per Section 360.12(6), flexible metallic tubing (FMT) is limited in use to 6 ft.
lengths.

For track lighting in non-dwelling occupancies, to comply with Section 220.43(B) a
load of 150 VA is to be included for every two (2) feet of lighting track. To solve this
problem , multiply 150 VA per linear foot by 80 ft. of track, by 125% (continuous
load), then divide by 2.

150 VA x 80 ft. x 1.25 = 15,000 = 7,500 VA
2 2

A door sill or curb of a transformer vault is to be of sufficient height to confine the
oil from the largest transformer in the vault, and in no case shall be less than 4
inches in height. Reference Section 450.43(B).

The Informational Note following Section 352.10(F) states PVC conduit, Type
Schedule 80 is identified for areas of physical damage.

Where a motor has a service factor of 1.00 marked on the nameplate, for the
purpose of selecting the rating or setting of the overload device, Section 430.32(A)(1) requires this device shall be selected to trip at not more than 115% of the motor nameplate full-load current rating. The power factor of the motor is not
to be a consideration when sizing overload devices. Therefore, nameplate current rating of
motor = 15 amperes x 1.15 = 17.25 amperes

Optional standby systems are intended to supply on-site generated power to
selected loads either automatically or manually. Article 702 applies not only to
permanently installed generators but also to portable generators. Optional standby
systems are intended to supply power to buildings or structures where life safety
does not depend on the performance of the system. Section 702.11(B) requires
where a portable generator is used as a non-separately derived system, the
equipment grounding conductor shall be bonded to the system grounding electrode.

Section 620.37(A) requires only electrical equipment and wiring used directly in
connection with the elevator may be installed in the hoistway and the machine
room. However, unless special permission is granted, Section 620.37(C) does not
permit main feeders for supplying elevators to be located in the hoistway.

Where straight pulls of conductors over 1000 volts are being made in junction
boxes, the length of the box shall not be less than 48 times the outside diameter of
the largest shielded or lead-covered conductor or cable entering the box. Reference Section 314.71(A).

In compliance with Section 332.24(1), the minimum bend radius for trade size in.
Type MI cable is to be not less than five times the external diameter of the cable.
The specified minimum bending radius of Type MI cable is intended to prevent
mechanical damage to the conductor insulation or the sheath that could result in a
short-circuit or ground-fault.

The intent of Section 110.75(D), requiring manhole covers to be over 100 lbs. or
requiring the use of tools to open, is to prevent unqualified personnel from entering
the manhole and being exposed to an electrical hazard.

Section 240.4(F) requires secondary overcurrent protection on delta-wye connected
transformers. In regard to this transformer, Table 310.15(B)(16) indicates size 4/0
AWG, 75C aluminum conductors to have an allowable ampacity of 180 amperes.
Since the ampacity of the conductors does not correspond to a standard
overcurrent protective device ampere rating, as permitted by Section 240.4(B)(3),
you may go up to the next standard ampere rating which is 200 amperes.

For the purpose of determining conductor fill in conduit, Note 9 to the tables located
in Chapter 9, requires multiconductor cable or cords of two or more conductors shall
be treated as a single conductor.

Section 314.27(C) addresses requirements for supporting ceiling-suspended
(paddle) fans. Outlet boxes specifically listed to adequately support ceiling-mounted
paddle fans are readily available. However, the boxes are not listed for use to
support fans that weigh more than 70 lb.

Where a motor control circuit conductor is tapped from the load side of the motor
overcurrent protective device, the size of the tapped conductor and the rating of the
overcurrent device are based on whether the conductor stays within the motor
control enclosure or leaves it. Due to the initial high inrush of current when the
motor starts, the overcurrent protection is similar to the overcurrent protection
provided for a motor and is allowed to be greater than the ampacity of the
conductor. Section 430.72(B)(2) permits where the conductors extend beyond the
motor control equipment enclosure, the rating of the protective device shall not
exceed the value specified in Column C of Table 430.72(B).

The intent of Section 200.6(E) is to provide a means of identifying the grounded
(neutral) conductor of multiconductor flat cable of 4 AWG or larger. The cable shall
be permitted to employ an external ridge on the grounded conductor.

As per Section 215.2(A)(1)(a), feeder conductors are required to have an ampacity
to carry 100% of the noncontinuous load, plus 125% of the continuous load:

20,000 VA x 100% = 20,000 VA
16,000 VA x 125% = 20,000 VA
Total = 40,000 VA

Apply the single-phase current formula to find the load:

I = power I = 40,000 VA = 166.6 amperes
volts 240 volts

In accordance with Table 310.15(B)(16), size 2/0 AWG 75 rated copper conductors
with an allowable ampacity of 175 amperes should be selected.

Column B of Table 220.55 shows the demand factor is 32% for 12 household
electric ranges having a rating of 8 kW each:

12 (ranges) x 8 kW x .32 = 30.72 kW demand

According to Section 210.52(A)(1), general-use receptacles located in a living room
or bedroom of a dwelling are to be spaced so that no point along the wall is more
than 6 ft. from a receptacle. In other words, the receptacles are to be spaced not
further than 12 ft. apart. The intent of this rule is receptacle outlets are to be
located so that an appliance or lamp with a flexible cord attached may be placed
anywhere in the room near a wall and be within 6 ft. of a receptacle, minimizing the
use of extension cords.

The requirement in Section 250.68(C)(1) limits grounding and bonding connections
to occur only within the first 5 ft. of where the piping enters a building or structure,
because of concerns that the use of PVC piping or fittings could interrupt the
electrical continuity of the metal water piping. The piping at this point is not
considered a grounding electrode, [only the underground portion is an electrode per Section 250.52(A)(1)].

Unless the ceiling support system is installed in accordance with the ceiling system
manufacturer's instructions, an independent means of secure support wires used to
support any type of wiring shall be provided and are permitted to be attached to the
ceiling assembly. The independent support wires shall be distinguishable from the
ceiling support wires by color, tagging, or other effective means. Reference Section 300.11(A)(2).

To determine the power factor apply the single-phase power factor formula:

Power factor = watts Power factor = 10 kW x 1000 = 10,000 = .869 = 87%
va 230 x 50 11,500

Section 314.28(E) provides requirements for the installation of power distribution
blocks as a termination or connection means for conductors contained within pull or
junction boxes. The use of power distribution blocks in junction boxes or pull boxes
is limited to enclosures over 100 cu. in

As mandated by Section 760.41(B), the circuit disconnecting means for NPLFA
circuits shall have red identification and shall be accessible only to qualified persons.

When given a conduit fill question like this where only one (1) conductor is smaller
than the remaining conductors of all the same size, in order to save time when
taking the test, refer to the conduit fill tables in Informative Annex C. Table C.3 of
Annex C indicates a trade size 3 in. flexible metal conduit may contain five (5) size
400 kcmil THWN conductors.

As per Section 225.18(2), overhead spans of open conductors over commercial
areas not subject to truck traffic are required to have a clearance of at least 12 ft.
from final grade, where the voltage to ground does not exceed 300-volts. The
voltage to ground on a 480Y/277-volt system is 277-volts, therefore the 12 ft.
clearance from final grade is permitted.

As allowed by the rules in Section 392.20(B)(1), Type MC cables operating at over
600 volts and those operating at 600-volts or less are permitted to be installed in a
common cable tray without a fixed barrier provided.

Mobile home park electrical systems must be calculated on the basis of the larger of
(1) not less than 16,000 volt-amperes (at 120/240-volts, single-phase) for each
mobile home lot or (2) the calculated load of the largest typical mobile home the lot
will accommodate. Reference Section 550.31(1). However, the ampacity of the
feeder-circuit conductors to each mobile home lot may not be less than 100 amperes
as per Section 550.33(B).

Section 250.104(A)(2) recognizes that the increased use of nonmetallic water piping
mains can result in the interior metal piping system of a multi-occupancy building to
be isolated from ground and from other occupancies. Therefore, the water pipe is to
be bonded to the panelboard or switchboard that serves only that particular
occupancy. The bonding jumper, in this case, is permitted to be sized according to
Table 250.122, based on the size of the overcurrent device supplying the occupancy.
Since the main circuit breaker is rated 400 amperes, a size 3 AWG copper bonding
jumper should be selected from Table 250.122.

For primary distribution systems exceeding 1000 volts on private property, the
service disconnecting is permitted to be located in a location that is not readily
accessible. Reference Section 230.205(A). The purpose of this rule is to prevent
ready access to unauthorized personnel.

In general, in compliance with Section 408.36, all panelboards are to be protected
by an overcurrent protective device. However, Exception No. 3 to this rule states,
for existing panelboards, individual protection shall not be required for a
panelboard used as service equipment for an individual residential occupancy.