First, apply the 3-phase current formula to find the load in amperes:

I = kVA x 1000 I = 75 kVA x 1000 = 75,000 = 208.1 amperes
E x 1.732 208 x 1.732 360.25

Size 4/0 AWG THWN copper conductors with an ampacity of 230 amperes should be
selected as shown in Table 310.15(B)(16).

Section 517.19(C) indicates the minimum number of receptacles to be provided for
an operating room of a health care facility is 36. At least 12 of the 36 receptacles
are required to be connected to either the normal system branch or the critical
branch circuit supplied by a different transfer switch than the other receptacles at the
same location.

Manhole openings for personnel are to be of an adequate size to provide ready
access and egress. Therefore, Section 110.75(A) requires round access openings for
a manhole to be not less than 26 inches in diameter.

You should have selected, in all these locations, because Sections 210.8(B)(1),(2)&(3) requires all 15- and 20-ampere, 125-volt receptacles located in nondwelling-type kitchens, bathrooms, and on rooftops to be GFCI protected. This
rule is in place to protect persons from accidental shock hazards and possible
electrocution when using cord-and-plug connected appliances and equipment.

In compliance with Section 430.6(A)(2), the ampere rating provided on the motor
nameplate is used to size the overload protective devices intended to protect the
motor. The basic premise of overload protection 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 system components from damaging overload currents.
Overload protection shall be selected to trip or shall be rated at no more than the
percentage values of the motor nameplate full-load current rating given in Section
430.32(A)(1). However, modification of this value shall be permitted as provided in 430.32(C). Since the motor in the question has a service factor of 1.15, multiply the nameplate current rating of 19 amperes times 140% to determine the maximum
setting or rating of the overload protection device.

19 amperes x 140% = 26.60 amperes

Whenever ground-fault protection of service equipment is provided for a health care
facility, whether by design or in compliance with the requirements in Section 215.10
or 230.95, an additional step of ground-fault protection shall be provided in all next
level feeder disconnecting means downstream toward the load. As per the
provisions of Section 517.17(B), ground-fault protection must be applied to every
feeder. The additional levels of ground-fault protection shall not be installed on the
load side of an essential electrical system transfer switch.

If the alternate source of supply for emergency lighting systems is a storage battery,
the battery source operates only if the normal source fails. A transfer means (throw
over switch) is to be provided to energize the emergency equipment from the
alternate supply when the normal source of supply is interrupted.
As per Section 700.12(A) the storage batteries are to be of a suitable rating and
capacity to supply and maintain the total load for a minimum period of 1 hours,
without the voltage applied to the load falling below 87 percent of normal.
Therefore, if the normal source of supply is 120 volts, then the storage batteries are
to maintain a voltage of not less than 105 volts for a period of not less than 1
hours.

120 volts x 87.5% = 105 volts

By requiring a permanently installed receptacle within 25 ft. of the HACR equipment, Section 210.63 improves worker safety by eliminating the need to use makeshift methods of obtaining 120 volt power for cord-and-plug connected equipment when
servicing and/or troubleshooting the HACR equipment.

Section 500.6(B) separates combustible dusts into three Class II groups - E, F and G
depending on their properties. When installed in Class II locations, equipment must
be approved not only for the class but also for the specific group and installation
standards. As indicated by Section 500.6(B)(1), atmospheres containing
combustible metal dusts such as aluminum or magnesium are considered to be
material Group E classifications.

Section 392.60(A) permits the use of cable tray as the equipment grounding
conductor in certain installations. The cable tray is to be electrically continuous and
effectively bonded and grounded. As per Sections 392.60(B)(1)&(3), aluminum or
steel cable trays are permitted to be used as equipment grounding conductors,
provided the cable tray sections and fittings are identified as an equipment
grounding conductor and the cable tray sections and fittings are durably marked to
show the cross-sectional area of the metal.

First find the VA of one circuit: 120 volts x 15 amperes = 1,800 VA

Next, divide the load of 9,600 VA by 1,800 VA (one circuit):

9,600 VA (load) = 5.3 = 6 circuits
1,800 VA (1 circuit)

The exception to Section 700.12(B)(3) permits where acceptable to the authority
having jurisdiction, where internal combustion engines are used as the prime
movers for emergency systems, they are permitted to be solely dependent on a
public utility gas system for their supply.

The requirements addressed in Section 210.52 apply to 125-volt, 15- or 20-ampere
receptacles located in dwelling units that are not part of a luminaire or appliance.
These receptacles are normally used to supply lighting and general-use cord-and-
plug connected appliances and electrical equipment. They are in addition to the
ones that are more than 5 ft. above the floor or within cabinets or cupboards.

Section 215.2(A)(1)(a) states feeder conductors are to have an ampacity of not less
than 125% of the continuous load, plus 100% of the noncontinuous load.

200 amperes x 125% = 250 amperes

Therefore, size 250 kcmil 75C copper conductors with an allowable ampacity of
255 amperes should be selected from Table 310.15(B)(16).

When applying demand factors for household electric ranges all of the same rating
over 12 kW through 27 kW, apply Note 1 and Column C of Table 220.55, which
states to increase the Column C demand value by 5% for each kW that exceeds 12 kW.

First find the portion that exceeds 12 kW: 21 kW - 12 KW = 9 kW

Next multiply 9 kW by 5%: 9 kW x 5% = 45% increase in Column C
8 kW (1 range - Column C demand value) x 45% = 3.6 kW increase
8 kW (Column C demand value) + 3.6 kW (increase) = 11.6 kW demand

In compliance with Section 240.4(C), the ampacity of the conductors shall be equal
to or greater than the overcurrent device, when over 800 amperes. Therefore, the
maximum standard size overcurrent devices that may be used to protect a busway
with an ampere rating of 1,100 amperes is 1,000 ampere rated overcurrent
protective devices. The standard ratings of overcurrent protective devices are listed
in Section 240.6(A).

Sections 695.4(B)(2)(a)(1), 695.5(B) and 695.5(C)(2) address the provisions
required for overcurrent protection for fire pumps. The requirement for sizing the
overcurrent protection so it is able to carry the locked-rotor current indefinitely is a
key factor to keeping the fire pump on line in the event of a fire. Due to the critical
life safety and property protection function of a fire pump, when a fire occurs it is
essential to keep the fire pump motors running as long as possible to help put out
the fire. If the locked-rotor amperes is not indicated on the motor nameplate, the
locked rotor currents found in Table 430.251(B) must be used to size the
overcurrent protection.

The intent of Section 680.43(B)(1)(a) is to prevent persons from coming into
inadvertent contact with luminaires or ceiling-suspended (paddle) fans located over
a spa or hot tub. When GFCI protection is not provided, the luminaires and/or fans
are to be installed at a height of not less than 12 ft. above the spa or hot tub.

Exception No. 1 to Section 250.68(A) does not require the terminations to be
accessible. Ground clamps and other connectors suitable for use where buried or
embedded in concrete must be listed for such use as per 250.70. Exception No. 2
permits connections, including the attachment of a compression lug to structural
steel, to be encapsulated by fireproofing material. This exception recognizes the
importance of maintaining the integrity of the structural fireproofing.

To solve this problem we need to take the following factors into consideration:

1) Branch-circuit conductors supplying a single A/C unit are to have a current-carrying capacity of at least 125% of the FLC rating of the unit. [440.32] 45 amperes x 125% = 56.25 amperes
2) The exception to 310.15(B)(3) permits conductors with Type XHHW-2 insulation to NOT be subject to the ambient temperature adjustments shown in Table 310.15(B)(3)(c), Ambient Temperature Adjustment for Raceways or Cables Exposed to sunlight on or Above Rooftops.
3) Because of the elevated ambient temperature, apply the ambient temperature correction factors shown in Table 310.15(B)(2)(a). 56.25 amperes .82 = 68.59 amperes
4) As mandated by Section 110.14(C), the temperature rating associated with the ampacity of a conductor shall be selected so as not to exceed the lowest temperature rating of any connected termination. Therefore, you should select size 4 AWG conductors with an ampacity of 85 amperes from the 75C column of Table 310.15(B)(16).

Section 240.8 prohibits the use of fuses or circuit breakers connected in parallel
unless they are factory assembled in parallel and listed as a unit.

As addressed in Section 210.4(B), all ungrounded conductors of a multiwire branch
circuit are required to be simultaneously disconnected to reduce the risk of shock to
installers and personnel working on equipment supplied by a multiwire branch
circuit.

As required by Section 430.32(A)(1) the overload device shall be rated based on the motor nameplate full-load current rating and modification of the values given on 430.32(A)(1) are permitted, therefore the values shown in Section 430.32(C) are allowed to be used. Due to the high temperature rise of the motor multiply the nameplate FLC of the motor, 54 amperes, times 130%.

54 amperes (nameplate current rating) x 130% = 70.2 amperes

Where a supplemental grounding electrode is required, Section 250.53(A)(2) states
the additional electrode(s) may be of a type specified in 250.52(A)(2) through
(A)(8). Supplemental grounding electrodes may be a concrete-encased electrode, a
ground ring, the metal frame of a building, a ground ring, rod and pipe electrodes
plus plate electrodes.

As permitted by Section 501.10(B)(2)(2), flexible metal conduit (FMC) may be used
for connection to motors in Class I, Division 2 locations. Section 502.10(A)(2) does
not recognize FMC for such use in Class II, Division 1 locations.

The intent of the rule addressed in Section 525.10(A) is to prevent unauthorized
personnel access to energized electrical equipment where they may encounter a
shock hazard or electrocution.

The reason Section 382.15(A) does not allow exposed nonmetallic extensions to be
on the floor or within 2 inches of the floor is because the raceway may be subject to
water and physical damage during housekeeping.

Under special conditions, special occupancies and capacity requirements, a building
is permitted to have more than one service, but Sections 230.2(A),(B),&(C) does
not recognize the conditions given in this question to merit an additional service.

There are no exceptions to the GFCI requirements for 125-volt, single-phase,
receptacles located in a residential garage. This requirement ensures that all 15-
and 20-ampere, 125-volt receptacles installed in garages provide GFCI protection
for the user of cord-and-plug connected appliances or other equipment regardless of
where the equipment is located in the garage. Refer to Section 210.8(A)(2).

As per Section 240.40, all fuses in circuits over 150 volts to ground, shall be
provided with a disconnecting means on their supply side.

Section 680.21(C) requires all single-phase 120-volt and 240-volt, 15- or 20-
ampere rated branch-circuits supplying permanently installed pool pump motors to
have GFCI protection regardless of the type of wiring method used.

Section 424.3(B) mandates that the branch circuits sized to supply fixed electric
space heating equipment are to be considered carrying a continuous load. Section 210.19(A)(1)(a) requires branch-circuit conductors are to have an ampacity of 125% of the continuous load(s) supplied. To solve this problem, first apply the
single-phase current formula to find the FLC of the heater:

I = kW x 1,000 I = 15 x 1,000 = 15,000 = 62.5 amperes (heater)
volts 240 240

Next add the FLC of the heater and the blower together and apply the continuous load factor:

62.5 amperes (heater)
+10.0 amperes (blower)
72.5 amperes x 125% = 91 amperes

For kitchen equipment in other than dwelling units, Section 220.56 permits the use
of the values given in Table 220.56 to be used for calculating the demand load:

19.00 kW - range
5.00 kW - water heater
0.75 kW - mixer
2.50 kW - dishwasher
2.00 kW - booster heater
2.00 kW - broiler
31.25 kW - total connected load x 65% = 20.31 kW

*NOTE: However the NEC states the demand shall not be less than the two
largest pieces of equipment. 19.00 kW + 5.00 kW = 24 kW demand

The effectiveness of underground metal water piping as a grounding electrode for electrical systems has long been recognized. As mandated by Section 250.52(A)(1), a metal underground water pipe must be in contact with the earth for at least 10 feet in order to qualify as an effective grounding electrode.

First, determine the load, in amperes, of the kitchen addition by using the 3-phase
current formula:

I = 54,000 VA = 54,000 = 149.89 amperes
208 x 1.732 360.25

Then, select the conductor size from Table 310.15(B)(16). Size 1/0 AWG THWN
conductors with an ampacity of 150 amperes should be selected.

Even under high-production conditions, the loads on transformer arc welders are
considered intermittent. Select the appropriate factor from Table 630.11(A) based
on the type of welder and the duty cycle of the welder to size the supply
conductors.

When a feeder supplies more than one arc welder, the conductor ampacity rating is
based on the sum of the current ratings of the individual arc welders determined by
applying the values shown in Table 630.11(A) and as per Section 630.11(B),
multiplying by 100% of the two largest welders, plus 85% of the third largest
welder, plus 70% of other fourth largest welder, plus 60 percent of all remaining
welders in the group.

60 amperes x .71 = 43 amperes x 100% = 43 amperes
60 amperes x .71 = 43 amperes x 100% = 43 amperes
50 amperes x .71 = 36 amperes x 85% = 31 amperes
50 amperes x .71 = 36 amperes x 70% = 25 amperes
40 amperes x .71 = 28 amperes x 60% = 17 amperes
40 amperes x .71 = 28 amperes x 60% = 17 amperes
TOTAL = 176 amperes

Section 352.20(B) states PVC conduit larger than trade size 6 in. shall not be used.

To solve this problem, apply the 3-phase power formula: P = I x E x 1.732, and multiply by 80%:

P = 600 amperes x 208 volts x 1.732 x 80% = 172,923 VA

As per Section 388.56, where surface nonmetallic raceways have covers not capable
of being opened in place, splices and taps of conductors shall be made only in
boxes.

Section 645.3(A), states the rules in Section 300.21 shall apply to penetrations of
the fire-resistant room boundary. Section 300.21 requires openings around
electrical penetrations through fire-resistant-rated walls, shall be firestopped using
approved methods to maintain the fire resistance rating. The intent of this rule is to
prevent the passing of products of combustion such as flame, excessive temperature
and smoke through fire-rated construction.

General method of calculation:

When applying demand factors for household electric ranges all of the same rating
over 12 kW through 27 kW, apply Note 1 and Column C of Table 220.55, which
states we are to increase the Column C demand value by 5% for each kW that
exceeds 12 kW.

First find the portion that exceeds 12 kW: 14 kW - 12 kW = 2 kW

Next multiply 2 kW by 5%: 2 KW x 5% = 10% increase in Column C demand value
17 kW (4 ranges - Column C demand value) X 10% = 1.7 kW increase
17 kW (Column C demand value) + 1.7 kW (increase) = 18.7 kW

Optional method of calculation: Section 220.84 states it is permissible to calculate the load of a feeder or service
that supplies three (3) or more dwelling units of a multifamily dwelling in
accordance with Table 220.84. As per Section 220.84(C)(3)b. the calculated load
to which Table 220.84 applies is based on the nameplate ratings of the electric
ranges. Table 220.84 shows the demand factor for four (4) electric ranges is 45%.

14 kW x 4 ranges = 56 kW x 45% (demand factor) = 25.2 kW demand

Column 1 of Table 392.22(A) indicates the maximum fill area of 9 in. wide ladder
type cable tray to be 10 square inches

Section 445.13 specifies the ampacity of the conductors from the generator
terminals to the first distribution device(s) containing overcurrent protection shall
not be less than 115 percent of the name plate current rating of the generator.
The first step is to determine the full-load current available at the generator
terminals by applying the 3-phase current formula.

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

The next step is to calculate the required ampacity of the conductors.

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

The final step is to select the proper size conductors from Table 310.15(B)(16).
Size 300 kcmil THWN conductors with an allowable ampacity of 285 amperes should
be selected.

Class II, Division 1 and 2 locations are defined in Section 500.5(C) as "hazardous
because of the presence of combustible dust." Therefore, Section 502.115(B)
requires enclosures for circuit breakers, switches, and motor controllers to be
dusttight or otherwise identified for the location where installed in a Class II,
Division 2 location.

Article 100 defines a hybrid system as a system comprised of multiple power
sources. These power sources may include photovoltaic, wind, micro-hydro
generators, engine-driven generators, and others, but do not include electrical
production and distribution network systems.

The 2014 Edition of the NEC has expanded Section 210.12(A) to include kitchens
and laundry areas of a dwelling in the list of locations to be provided with AFCI
protection to provide increased safety by reducing the number of arcing events in
dwellings.

To solve this problem take into consideration the following related information
regarding calculations for dwelling units:

1) According to Section 220.12, a unit load of 3 VA as specified in Table 220.12 shall constitute the minimum lighting load. The calculation floor area shall not include garages and open porches.
2) As per Section 220.52(A), each small appliance circuit shall be calculated at 1,500 VA each.
3) Section 220.52(B) specifies a load of not less than 1,500 VA is to be included for the laundry branch circuit.
4) As permitted by Section 220.42, the demand factors specified in Table 220.42 shall apply to that portion of the total branch circuit load calculated for general illumination.

Therefore, to calculate the demand load do the math as follows.

4,000 sq. ft. + 2,000 sq. ft. = 6,000 sq. ft. x 3 VA = 18,000 VA
three small appliance circuits @ 1,500 VA each = 4,500 VA
one laundry circuit @ 1,500 VA = 1,500 VA
Total connected load = 24,000 VA

1st 3,000 VA @ 100% 3,000 VA
24,000 VA - 3,000 VA = 21,000 VA (remainder) @ 35% = 7,350 VA
Total demand load = 10,350 VA

In compliance with Section 430.6, where flexible cord is used to supply motors, the
size of the conductors shall be selected in accordance with Section 400.5. For
general motor applications, Section 430.6(A)(1) indicates the full-load current
values given in Table 430.250 are to be used where sizing the conductors for a 3-
phase ac motor. Section 430.22 requires conductors that supply a single motor
used in a continuous duty application shall have an ampacity of not less than 125%
of the motor full-load current rating.

Locate the FLC of the motor, 40 amperes, as shown in Table 430.250, then as per Section 430.22 multiply by 125% to determine the required ampacity of the conductors to supply the motor.

FLC of 30 hp motor = 40 amperes x 125% = 50 amperes
Size 4 AWG SOW cord with an allowable ampacity of 60 amperes should
be selected from Column A of Table 400.5(A)(1).

As mandated by Section 525.5(B)(2), at fairs, carnivals and similar events, portable
structures, which includes rides, attractions and vendor booths are not permitted
within an area of 15 ft. horizontally of conductors operating in excess of 600 volts.
This area extends from the overhead conductors down to grade level.

In general, flexible cords and cables are not permitted to be attached to building
surfaces. However, the exception following Section 400.8(4), permits flexible cords
and cables to be attached to building surfaces in accordance with the provisions
indicated in Section 368.56, which provides the requirements for the installation of
flexible cords installed as branches from busways. Section 368.56(B)(2) permits
flexible cord and cables to be attached to building surfaces where the length of the
cord or cable from a busway plug-in device to a suitable tension "take-up" support
does not exceed 6 feet.

Section 225.6(A)(1) requires overhead spans of open individual conductors of 1000
volts or less, and up to 50 ft. in length to be not less than 10 AWG copper in size.

Section 430.2 defines a controller as any switch or device that is normally used to
start and stop a motor by making and breaking the motor circuit current.

As per Section 409.106, the spacing requirements between live uninsulated metal
parts in feeder circuits of 480-volt industrial control panels and bare metal parts of
the enclosure shall be as shown in Table 430.97(D). This table indicates a
clearance of not less than 1 inch must be maintained between the components.

Section 336.104 states, the insulated conductors of Type TC cables shall be in sizes
18 AWG to 1000 kcmil copper, nickel or nickel-coated copper.

All electric pool water heaters shall have the heating elements subdivided into loads
not exceeding 48 amperes and protected at not over 60 amperes. Refer to Section 680.9.

Sections 700.5(A) and 701.5(A) require transfer switches to be automatic.

According to Section 338.10(B)(4)(a), Type SE cable is only limited to operating at
a 60C ampacity when it is installed in thermal insulation. Type SE cable is
permitted to have conductors with either 75C or 90C insulation, and any
adjustment or correction is to be based on the temperature rating of the conductors
in the specific SE cable. If there is not temperature rating marked on the surface of
the conductors, the conductors have a 75C insulation temperature rating, and
ampacity adjustment or correction is based on that rating.
Where Type SE cable is installed in thermal insulation, the adjusted and/or
corrected ampacity of the conductors cannot exceed those shown in the 60C
column of Table 310.15(B)(16).

Because grounded conductors are current-carrying, Section 200.2(B) requires
grounded conductors be connected to a terminal or busbar that is specifically
intended and identified for connection of grounded or neutral conductors. The
continuity of a grounded conductor shall not depend on a connection to a metallic
enclosure, raceway or cable armor.

Connecting grounded conductors to a separate equipment grounding terminal or
busbar (that is directly connected to a metal enclosure) results in the enclosure
becoming a neutral conductor between the equipment grounding terminal and the
point of connection for the grounded conductor.

In compliance with Section 390.8, where a receptacle outlet is removed from an
underfloor raceway, the conductors supplying the outlet shall be removed from the
raceway.

The intent of Section 110.26(A) is to provide enough space for personnel to perform
maintenance and examination of electrical equipment without jeopardizing worker
safety. Examples of such equipment include panelboards, switchboards, motor
control centers, motor controllers, disconnecting switches, and controls on heating
and air-conditioning equipment. Where exposed live parts of the equipment, having
a voltage to ground of 151-600 volts, are on both sides of the working space,
Condition 3 of Table 110.26(A)(1) is to be applied. Under this condition the working
space is required to be not less than 4 feet.

As required by Section 550.30, the secondary distribution system for a mobile home
lot is to be single-phase, 120/240-volts. Section 550.31(1), mandates each
mobile home lot is to be calculated at a minimum of 16,000 VA; this is the value to
be used for this calculation. A demand factor of 24% is permitted to be applied as
shown in Table 550.31. First determine the demand load:

25 lots x 16,000 VA (minimum) = 400,000VA
"‹ X .24 (demand factor) 96,000 VA (demand load)

Next determine the load in amperes:

I = power I = 96,000 VA = 400 amperes
volts 240 volts

First, apply the 3-phase current formula to find the full-load amperage rating of the
transformer:

I = kVA x 1000 I = 150 x 1000 = 150,000 = 416 amperes (FLA)
E x 1.732 208 x 1.732 360.25

Next, subtract the existing load from the transformer FLA:

416 amperes (transformer FLA)
- 212 amperes (existing load)
= 204 amperes (additional load)

The reason the insulated isolated grounding conductor of isolated receptacles is
not bonded to the box is for the reduction of electrical noise (electromagnetic
interference) on the grounding circuit. This conductor may originate in the service
panel, pass through any number of subpanels without being connected to the
equipment grounding bus, and terminate at the isolated-ground-type receptacle
ground terminal. Reference Section 250.146(D).

According to Section 600.5(B)(2) branch circuits that supply electric signs with
incandescent or fluorescent lighting are limited to ratings of 20 amperes.

Section 800.113(B)(1) permits Type CMP communications cables of not more than 4
ft. in length to be installed in fabricated ducts used for environmental air if they are
directly associated with the air distribution system.

As per Section 600.6 the switch or circuit breaker for electric signs and outline
lighting systems shall open all ungrounded (phase) conductors on multi-wire branch
circuits. This rule complies with the rule mandated in Section 210.4(B).

The primary objective of Section 210.52(H) is to minimize the need to use extension
cords to supply utilization equipment and to minimize the strain or damage to cords
and receptacles for dwelling unit receptacles.

Where constant wattage heating cables are installed in concrete floors, Section 424.44(A) requires the heating cables to not exceed 16 watts per linear foot of cable.

Exception No. 2 following Section 408.36, limits a panelboard protected on its
supply side by two main circuit breakers or two sets of fuses having a combined
rating not greater than that of the panelboard, to no more than 42 overcurrent
devices. This type of panelboard (split-bus) is commonly installed for dwelling units.

In regard to an irrigation pond, to prevent damage to equipment and motors, when
the water level reaches the height of the established electrical datum plane, the
service must disconnect. Reference Section 682.11.

Section 404.14(E) clarifies general-use dimmer switches are not permitted to
control receptacles, cord-and-plug-connected table and floor lamps, ceiling fans, or
fluorescent luminaires. They are only to be used to control permanently installed
incandescent luminaires.

The purpose of Section 410.97 is to prevent igniting combustible material near
lampholders.

Section 410.54(C) states pendant conductors longer than 3 ft. shall be twisted
together where not cabled in a listed assembly. This rule ensures pendant
conductors are installed in a neat and workmanlike manner.

As per Section 285.28 grounding electrode conductors installed in metal enclosures
housing a SPD shall comply with the requirements of Section 250.64(E). This
section requires the housing to be made electrically continuous by bonding both
ends to the grounding electrode conductor.

As specified by Section 250.52(A)(2)(1), the metal frame of a building or structure
can qualify as a grounding electrode if there is structural steel in direct contact with
the earth for at least 10 ft. or if the structural steel is encased in concrete in direct
contact with the earth for at least 10 ft.

Circuits supplying autotransformer-type dimmers are not permitted to exceed 150
volts between conductors. With this type dimmer, any desired voltage may be
applied to the lamps of luminaires, from full-line voltage to voltage so low that the
lamps provide no illumination by means of a movable contact tap. This type of
dimmer produces very little heat and operates at high efficiency. Reference Section 520.25(C).

Use Table 220.54 and first find the demand factor, in percent, for 12 dryers:

47% - 1% (minus 1% for each dryer exceeding 11) = 46% demand factor

12 dryers x 5,500 watts = 66,000 VA (connected load) x 46% = 30,360 VA demand

As per Section 503.130(A), luminaires installed in Class III, Divisions 1 and 2 are to
be marked to show the maximum wattage of the lamps that shall be permitted
without exceeding an exposed surface temperature of 329F. This rule is in place
to prevent the overheating of luminaires which may cause igniting combustible
fibers/flyings that are present in Class III locations. Fibers/flyings are hazardous not
only because they are easily ignited, but also flames spread through them quickly.
Such fires travel with a rapidity approaching an explosion and are commonly called
flash fires.

Most motor applications are continuous duty, meaning they operate at a constant
load for an indefinitely period of time. For motors that are not continuous duty, the
motor nameplate current rating and Table 430.22(E) are used to determine the
branch circuit ampacity. This table indicates conductors supplying a continuous-
rated, varying duty motor shall have an ampacity of at least 200% of the motor
nameplate current rating.

Section 330.30(B) contains the general requirements for supporting and securing
Type MC cable. It must be secured at least every 6 ft.

Cover plates or the receptacles themselves are required to be identified where
supplied by the essential electrical system in a hospital. This identification
requirement applies to all receptacles supplied by the life safety and critical
branches of the hospital essential electrical system. The NEC does not address a
specific method of identification required, but the color red is used in many health
care facilities to identify receptacles supplied by the essential electrical system.
Reference Section 517.30(E).

Table 310.15(B)(16) shows size 4/0 AWG THWN copper conductors to have an
allowable ampacity of 230 amperes. Since this value does not correspond with a
standard size overcurrent protective device, according to Sections 240.4(B)(2)&(3),
you are permitted to go up to the next standard size rating of 250 amperes as
indicated in Section 240.6(A).

All conductors of a branch circuit, including the grounded conductor, supplying a
motor fuel dispensing pump, must be provided with a switch or special-type circuit
breaker that simultaneously disconnects all conductors. The intent of the rules
specified in Section 514.11(A) is that no energized conductors are in the fuel
dispenser vicinity during maintenance or inspection.

The purpose of Table 110.26(A)(1) is to provide enough working space in front of
electrical equipment for personnel to perform maintenance and inspections without
jeopardizing worker safety. This table indicates where the voltage to ground
present is not more than 150 volts, a minimum clear distance required in front of
the equipment is 3 ft.

Equipment grounding conductors are to be sized in accordance with Table 250.122,
based on the rating or setting of the overcurrent device ahead of the equipment. In
this situation, the overcurrent protective device is rated 60 amperes, therefore the
minimum size copper equipment grounding required is 10 AWG.

Section 450.11(A) recognizes the information given on the nameplate of a
transformer includes the manufacturer, the kVA rating of the transformer and the
voltage. The overcurrent protection is not required to be marked on the transformer
nameplate.

A combination surface nonmetallic raceway is used primarily to contain conductors
to supply power to receptacles, CATV and communications outlets, therefore, the
different systems are required to be run in separate compartments. Reference Section 388.70.

To ensure the explosionproof integrity of the conduit system, where the
explosion-proof equipment is provided with metric threaded entries,
Section 500.8(E)(2) mandates approved adapters from metric threads to
NPT (National Standard Pipe Taper) threads shall be used.

Section 450.21(A) requires transformers rated for more than 1000 volts and not
over 112 kVA to have a clearance of not less than 12 in. from combustible
material.

In order to maintain a safe distance from the water level of a swimming pool to
conductors of 0-750 volts, Table 680.8(A) indicates a clearance of at least 22 ft. is
required.

The demand factors specified in Table 220.42 may be applied to calculate the
general lighting demand loads for dwelling units.

First, convert into VA: 205.4 kVA x 1,000 = 205,400 VA

Next, apply the values given in Table 220.42:

first 3,000 VA @ 100% = 3,000 VA
3,001 to 120,000 VA @ 35% = 117,000 VA @ 35% = 40,950 VA
remainder 205,400 VA - 120,000 VA = 85,400 VA @ 25% = 21,350 VA
Demand = 65,300 VA

Finally, determine the kVA: 65,300 VA = 65.3 kVA
1,000

The GFCI protection requirements for high-pressure spray washers are addressed in Section 422.29. This requirement was initiated because at least ten documented electrocutions have been linked to nonindustrial high pressure spray washing
machines of the type purchased by, or rented to consumers. These cord-and-plug connected machines present shock hazards to users in wet conditions.

The same shock hazard exist for 3-phase machines as for single-phase. However, at this date, there are no 3-phase, 240-volt listed GFCI devices available to be located in the attachment plug or in the cord of the appliance, or listed GFCI devices intended for use on circuits operating greater than 150-volts to ground.

Section 422.13 recognizes fixed storage-type water heaters with a capacity of 120
gallons or less, may be operated at an indefinite period of time; therefore, they are
considered a continuous load.

First, apply the single-phase current formula to determine the load in amperes:

I = power I = 36,000 VA = 150 amperes load
volts 240 volts

Next, due the elevated temperature, divide the load of 150 amperes by .75, the
temperature correction factor given in Table 310.15(B)(2)(a):

required ampacity = 150 amperes = 200 amperes
.75

Then, size 3/0 AWG 75C copper conductors with an allowable ampacity of 200
amperes should be selected from Table 310.15(B)(16).

Color coding shall be permitted to identify intrinsically safe conductors where they
are colored light blue and where no other conductors of the same color are used.
Reference Section 504.80(C).