Part III of Article 310- Conductors for General Wiring, covers the general installation requirements for conductors rated up to and including 2000 volts. Section 310.14(B) tells the reader the ampacity of each conductor within a raceway needs to be corrected for ambient temperatures other than 30°C (86°F). Using the values shown in Table 310.15(B)(1), multiply the ampacities of the conductors specified in the ampacity tables by the appropriate correction factor shown in Table 310.15(B)(1) to correct the ampacities of the conductors. Also, Section 310.14(C) tell us the ampacity of each conductor is to be adjusted as shown in Table 310.15(C)(1) where the number of current-carrying conductors within a raceway or cable exceeds three. Again, multiply the conductor ampacities as shown in the ampacity tables by the percentage values given in Table 310.15(C)(1).

Part VI of Article 250 explains the wiring methods and installation requirements for equipment grounding and equipment grounding conductors. Section 250.118 lists the approved types of equipment grounding conductors. 250.122(5)d. specifies where flexible metal conduit (FMC) is longer than 6 ft. it is not considered an effective ground-fault current path.

Article 210 provides the general requirements for branch circuits. Section 210.8(A)(2) requires all 125-volt through 250-volt, single-phase receptacles installed in residential garages to be provided with ground-fault protection for personnel. There are no exceptions to this rule, the receptacles must be provided with GFCI protection for the user of appliances or other equipment regardless of where the receptacle is located in the garage.

The uses and ampacity ratings of conductors for general wiring are found in Article 310. Section 310.3 specifies the minimum size of conductors for general wiring shall be 14 AWG copper or 12 AWG aluminum except as permitted elsewhere in the Code.

Article 406 covers the rating and installation of receptacles. Section 406.9(B)(1) addresses the installation of receptacles of 15- and 20-amperes placed in a wet location and specifies where the plug-and-cord connection to receptacles is in a wet location, the enclosure is required to be weatherproof regardless of whether or not the plug is inserted.

Section 310.12 of Article 310, Conductors for General Wiring, permits the values given in Table 310.12 for use when sizing service and feeder conductors under this condition. The table indicates size 4/0 AWG aluminum conductors are the smallest size permitted for a 200-ampere rated service if no adjustment or correction factors are applied. Note, the service-entrance conductors for dwellings, under this condition, is reduced in size in relation service-entrance conductors for commercial and industrial occupancies due to the dwelling unit's diversified load.

Article 314 governs the installation and use of all outlet and device boxes. Table 314.16(A) shows six (6) size 12 AWG conductors are permitted in the FS box however, Section 314.16(B)(4) tell us the number of conductors allowed in the box shall be reduced by two (2) due to the receptacle contained in the FS box. Therefore, the box is permitted to have only four (4) size 12 AWG conductors.

Part III of Article 210 provides the general requirements for the required 125-volt, single-phase 15- and 20-ampere receptacle outlets in a dwelling unit. Section 210.52(C)(2)(b) specifies at least one receptacle outlet shall be located within 2 feet of the outer end of a peninsular countertop or work surface. Additional required receptacle outlets are permitted to be located as determined by the installer, home owner, or builder. This rule eliminates the need for extension cords.

Section 210.12 of Article 210, Branch Circuits, explains the rules for AFCI protection of 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices in a dwelling unit. 210.12(A)(4)b. calls for the conductors to have length restrictions to the first outlet from the overcurrent device, based on the size of the conductors; 50 feet for 14 AWG and 70 feet for 12 AWG conductors. This rule is in place to restrict voltage-drop and prevent nuisance tripping of the overcurrent protection device.

The rules for service equipment and service conductors and their installation requirements are found in Article 230. Section 230.85 tells the reader the required emergency disconnect provided for one- and two-family dwellings is to be installed in a readily accessible outdoor location. This mandate was established because of the need for first responders and utility personnel to have a way to safely remove power from the house in an emergency.

The high-leg, the phase having the higher voltage to ground, is common on a 240/120-volt, 3-phase, 4-wire center tap grounded system and Section 408.3(E)(1) explains the high leg must be designated as the “B phase”. Section 110.15 requires the high leg to be identified and marked as orange in color or another effective means of identification, because the high leg voltage can be 208-volts. This identification is intended to prevent problems caused by the lack of standardization where metered and nonmetered equipment are installed in the same installation.

The exception to 408.3(E)(1) recognizes the fact that metering      compartments supplied by utility companies have been standardized with the high leg as the “C phase” rather than the “B phase”. When encountering a panelboard or switchboard, electricians should always test each phase to ground to determine if a high leg is present.

Section 210.8(A) tells us, all 125-volt through 250-volt receptacles installed  in locations specified in 210.8(A)(1) through (A)(11) and supplied by single-phase branch circuits rated 150 volts or less to ground are required to have GFCI protection. This means all 125-volt through 250-volt receptacles require GFCI protection where installed to serve kitchen countertop surfaces, where installed within 6 ft. from the top inside edge of the bowl of the sink, and where installed in laundry areas.  Wet clothes and puddles of water can pose a shock hazard to anyone using any appliance in a laundry area.

Residential service-entrance conductors are permitted to be sized at slightly higher ampacity values than the ampacity values found in Table 310.16 primarily due to the diversity of loads associated with dwelling units.  Therefore, Section 310.12(A) allows the service-entrance conductors to have an ampacity not less than 83% of the service rating and the values given in Table 310.12(A) are permitted to be applied.

The percentage values shown in Table 310.15(C)(1) are to be applied to the ampacity (current-carrying capacity) of conductors when four (4) or more current-carrying conductors are installed in the same raceway or cable.  When more than three (3) current carrying conductors are in a common raceway or cable, the temperature rises inside the conduit or cable because each current-carrying conductor adds to the heat inside the conduit or cable and conductors which are close together cannot dissipate the heat as well as evenly spaced conductors. This has the same effect on the insulation of a conductor as elevated ambient temperature.  Therefore, the ampacity of each of the current-carrying conductors in the raceway is reduced.

In order for the hermetic motor-compressor to start without tripping the  circuit breaker used as the disconnecting means, Section 440.12(A)(1) requires the ampere rating of the disconnecting means to be at least 115% of the motor-compressor nameplate rated-load current or branch-circuit selection, whichever is greater.

You should have selected 3/0 AWG. Table 310.16 gives the ampacities of insulated conductors of 0 through 2000 volts with not more than three current-carrying conductors in a raceway or cable, and the wiring is installed in a 30°C (86°F) ambient temperature environment.  Where the conductors are installed in a location where the ambient temperature is other than 86°F, you are required to apply the correction factor values shown in Table310.15(B)(1)(1), based on the operating temperature of the conductors and the ambient temperature.  Where a raceway or cable contains more than 3 current-carrying conductors, the adjustment factor values indicated in Table 310.15(C)(1) are to be implemented. Notice the adjustment factors of the conductors shown in this table are not applicable where the raceway or cable has a length not exceeding 24 in. [310.15(C)(1)(b)]

As per Section 110.12, electrical equipment shall be installed in a professional and skillful manner. The attention to this section in the Code reminds us how important it is to be a professional and take pride in our work. The decision of how professional and skillful an installation is performed is ultimately a judgment call made by the local inspector having jurisdiction.

Article 314 covers the installation and use of outlet, device, and pull boxes   depending on their use.  Section 314.27(C) specifically addresses boxes at ceiling-supported (paddle) fan outlets.  Outlet boxes specifically listed to support ceiling-mounted paddle fans are to be marked by their manufacturer as suitable for this use and shall not support ceiling-suspended (paddle) fans that weigh more than 70 pounds.  Outlet boxes used to support ceiling-suspended (paddle) fans that weigh more than 35 pounds are to be marked indicating the maximum weight to be supported.

To find the full-load current rating of the secondary terminals on the single- phase transformer, apply the single-phase current formula as shown:
 
          I = 112.5 kVA x 1000  = 112,500  = 468.75 amperes 
                     240 volts               240

The rule established by Section 200.11 does not permit the grounded (neutral) conductor to be attached to any terminal or lead so as to reverse the designated polarity.  The intent of this rule is to prevent a grounded (neutral) conductor from being attached to an ungrounded (hot) terminal or lead which creates a shock hazard or a ground-fault.

Part VI of Article 250 covers the wiring methods and installation requirements for equipment grounding and equipment grounding conductors. Section 250.118 lists the approved types of equipment grounding conductors and liquid-tight flexible metal conduit (LFMC) is included in the list. However, 250.122(6)d. tells the reader where the flex is longer than 6 feet it is not considered an effective type of equipment grounding conductor and a wire-type equipment grounding conductor needs to be installed.

Article 430 covers motors, motor conductors, motor protection, motor controllers, motor control circuits, and motor control centers. Section 430.6(A)(1) explains for a motor of this type, Table 430.250 that shows the full-load current (FLC) of motors, shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault protection, instead of the actual ampere rating marked on the motor nameplate. Section 430.6(A)(2) indicates the ampere rating (FLA) provided on the motor nameplate is used to size the overload protective devices that protects the motor, motor controller, and motor branch-circuit conductors. Overloads are not a fault condition, overloads happen when there is excessive current in the circuit. An overload is where the current is more than the equipment ampere rating and the overload may result in overheating and damaging equipment. Overload protection does not protect against short-circuits or ground-fault currents.

Part II of Article 250 addresses the general requirements for system grounding and bonding of alternating-current systems to be grounded. Section 250.24(B) requires an unspliced main bonding jumper to connect the equipment grounding conductor and the service disconnect enclosure to the neutral (grounded conductor) within the enclosure. The size of the main bonding jumper is determined in accordance with Table 250.102(C)(1).

The provisions of Article 680 apply to the installation and wiring methods of storable or permanently installed swimming pools, hot tubs and spas, and to their metallic auxiliary equipment, such as pumps and similar equipment. Section 680.41 in Part II of Article 680 was initiated because, a local disconnecting device, not less than 5 ft. away from the hot tub, that is capable of being used in an emergency is needed for hot tubs and spas to allow rapid disconnection if someone becomes entrapped by the water recirculation system intake.

Article 440 applies to air-conditioning and refrigeration equipment and to branch circuits and controllers for the equipment. Section 440.14 prohibits the disconnecting means to be located on panels that are designed to allow access to the equipment or to obscure the equipment nameplate.

The rules regarding the use and installation of rigid metal conduit (RMC) are found in Article 344. As per Section 344.30(A), as a general rule, RMC is required to be supported least every 10 feet and within 3 feet of each outlet box, junction box, panelboard or any similar cabinet unless otherwise permitted by 334.30(B). Section 334.30(B)(3) permits the exposed vertical risers of RMC from industrial machinery or fixed equipment to be supported at intervals of 20 feet when the conduit has threaded couplings, fastened at the top and bottom of the riser, and no other means of immediate support is readily available.

Article 445 contains installation and other requirements for generators. Section 445.13 specifies, the ampacity of the conductors from the generator terminals to the first overcurrent protection shall not be less than 115 percent of the nameplate current rating of the generator. Apply the single-phase current formula to solve this problem. I = P ÷ E

  I =  22 kw x 1000  = 22,000  = 92 amperes x 1.15 = 106 amperes
          240 volts            240
 

Article 605 covers electrical equipment, wiring methods and conductors installed in office furnishings. Section 605.9(D) does not permit an individual office furnishing to contain multiwire circuits. Although multiwire branch circuits are not permitted in cord-connected office furnishings, they may be supplied by one phase of a multiwire branch circuit.

Part VI of Article 250 explains the wiring methods an installation requirements for equipment grounding and equipment grounding conductors. Section 250.118 lists the approved types of equipment grounding conductors. 250.118(5)c. specifies where flexible metal conduit (FMC) exceeds trade size 1¼ in. it is not approved for use as an equipment grounding conductor and an additional wire-type equipment grounding conductor needs to be installed in the flex.

Part II of Article 680 applies to the rules governing the installation and wiring methods of permanently installed swimming pools. Section 680.21(A) mandates when wiring a swimming pool pump motor, the raceway containing the supply conductors shall also contain an insulated copper equipment grounding conductor not smaller than 12 AWG in order to have an effective ground-fault path.

Part II of Article 242 (Overcurrent Protection) covers surge-protective devices (SPDs) permanently installed on premises wiring systems of not over 1000 volts. Type 1 SPDs are to be connected to the supply side of the service disconnect.  In Section 242.13(B)(1)-(4), the Code gives four locations for connecting the SPD grounding lead and any of these locations are acceptable.

The ampacity of a conductor is to be selected from the column of Table 310.16 that corresponds with the metallic element, insulation and temperature rating of the conductor. The 75°C column of Table 310.16 conveys the size 4 AWG THW copper        conductors have an ampacity of 85 amperes.  However, in compliance with the rules in Section 110.14(C), since the conductors are connected to 60°C terminations, the ampacity must be selected from the 60°C column, that shows the ampacity of the size 4 AWG conductors to be 70 amperes.  The weak point of any electrical system is where conductors are spliced or terminated. The temperature rating of the conductor, metallic element, along with the size of the conductor determines how much current it is permitted to carry, but it cannot be greater than the temperature rating of the termination points.

As indicated in Section 110.26(E)(1)(c) the dedicated equipment space for  outdoor installed switchgear, panelboards and motor control centers shall be equal to the width and depth of the equipment and extends to a height of 6 ft. above the equipment.  No gas piping, ductwork, water piping, refrigeration lines, irrigation equipment, compressed air lines and other non-electrical equipment is permitted to be installed in this space.  This space above and below the equipment is dedicated for the electrician to install electrical raceways in and out of the equipment.

Article 215 introduces the installation requirements, sizing, and overcurrent protection for feeder conductors not over 1000 volts. Section 215.2(A)(1)(a) requires feeder conductors to have an ampacity of not less than 125% of the continuous load, plus 100% of the continuous load.
            
            200 amperes x 125% = 250 amperes
          
Therefore, size 250 kcmil 75 copper feeder conductors with an ampacity of 255 amperes should be selected from Table 310.16

As addressed in Section 250.64(D)(1), for a service or feeder with two or more disconnecting means in separate enclosures supplying a building or structure, a common grounding electrode conductor and grounding electrode conductor taps shall be installed. A grounding electrode conductor shall extend to the inside of each disconnecting means enclosure.  The tap conductors are to be connected to the common electrode conductor.  Section 250.64(D)(1)(3) recognizes a method of connections to an accessible copper or aluminum busbar with minimum dimensions of ¼ inch thick by 2 inches wide as an acceptable method to connect the taps to the common grounding electrode conductor.

The provisions of Part II in Article 440, gives the requirements for the disconnecting means for air conditioning and refrigerating equipment.  As noted in Section 440.12(A)(1), the disconnecting means shall have an ampere rating of at least 115% of the nameplate rated-load current of the equipment or branch-circuit selection current, whichever is greater.

The minimum burial depth requirements for conductors and cables not exceeding 1000 volts are located in Table 300.5(A) of Article 300.  Column 3 of Table 300.5(A) indicates the PVC to have a permitted burial depth of not less than 18 inches from final grade, where the PVC doesn't cross under any public streets, roads driveways or alleys.

Before derating, Table 310.16 shows the ampacity of size 2 AWG THHN copper conductors at 86ºF is 130 amperes.  Because of the elevated ambient temperature, 130 amperes is to be multiplied by 0.91, the ambient temperature correction factor in Table 310.15(B)(1)(1), and by 0.80, the adjustment factor in Table 310.15(C)(1), because of the four (4) current-carrying conductors in the raceway.   
 
         Solution: 130 amperes x .91 x .8 = 94.64 amperes

As explained in Section 300.5(D)(2), the underground installed service conductors are to have a warning ribbon placed not less than 12 inches above the conductors to have their location identified. This rule is in place, because these circuit conductors are not protected from short circuit and overload. The warning ribbon reduces the risk of an accident, such as an electrocution or an arc-flash incident, when digging near underground service conductors that are not encased in concrete.

Part II of Article 220 provides the calculation methods for branch-circuit loads. Section 220.42, confirms the minimum unit lighting load for dwellings shall not be less than 3 VA per sq. ft.  The minimum lighting load is to be determined using the minimum unit load and the floor area for dwelling occupancies.
 
            First, find the minimum lighting load, in VA:
            3 VA x 1,950 sq. ft. = 5850 VA
 
            Next, find the VA of a 120-volt, 15 ampere circuit:
            120 volts x 15 amperes = 1800 VA
 
            Finally, divide the VA of the load by the VA of the circuit:
 
             5850 VA (load)  = 3.25 = 4, 120-volt, 15 ampere circuits
            1800 VA (circuit)