See Part 3 for the Introduction for Article 314

Transcription

1 See Part 3 for the Introduction for Article Covers and Canopies When the installation is complete, each outlet box must be provided with a cover or faceplate, unless covered by a fixture canopy, lampholder, or similar device. See Figure Boxes and Conduit Bodies for Conductors 4 AWG and Larger. Boxes and conduit bodies containing conductors 4 AWG and larger must be sized so the conductor insulation will not be damaged. Author s Comments: The requirements for sizing boxes and conduit bodies containing conductors 6 AWG and smaller are contained in Where conductors 4 AWG or larger enter a box or other enclosure, a fitting that provides a smooth, rounded, insulating surface, such as a bushing or adapter, is required to protect the conductors from abrasion during and after installation [300.4(F)]. Figure Figure (A) Nonmetallic or Metallic. Nonmetallic covers or plates are permitted on any box, but metallic faceplates, where used, must be bonded to an effective ground-fault current path in accordance with [250.4(A)(3)]. See (C). Author s Comment: Switch faceplates must be grounded (bonded) to an effective ground-fault current path [404.9(B)], and receptacle faceplates must be grounded (bonded) to an effective ground-fault current path [406.5(A)]. Figure Mike Holt Enterprises, Inc NEC.Code 139

2 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules (A) Minimum Size. For raceways containing conductors 4 AWG or larger, the minimum dimensions of boxes and conduit bodies must comply with the following: (1) Straight Pulls. The minimum distance from where the conductors enter to the opposite wall cannot be less than eight times the trade size of the largest raceway. Figure U Pulls. When a conductor enters and leaves from the same wall, the distance from where the raceways enter to the opposite wall cannot be less than six times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall and row. Figure Figure Figure (2) Angle and U Pulls. Angle Pulls. The distance from the raceway entry to the opposite wall cannot be less than six times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall and row. Figure Figure Rows. Where there are multiple rows of raceway entries, each row is calculated individually and the row with the largest distance must be used. Distance Between Raceways. The distance between raceways enclosing the same conductor cannot be less than six times the trade size of the largest raceway, measured from the raceway s nearest edge-to-nearest edge. See Figure Exception: When conductors enter an enclosure with a removable cover, such as a conduit body or wireway, the distance from where the conductors enter to the removable cover cannot be less than the bending distance as listed in Table 312.6(A) for one wire per terminal. Figure (3) Smaller Dimensions. Boxes or conduit bodies of dimensions less than those required in (A)(1) and (A)(2) are permitted, if the enclosure is permanently marked with the maximum number and maximum size of conductors permitted. (C) Covers. All pull boxes, junction boxes, and conduit bodies must have a cover that is suitable for the conditions. Nonmetallic covers or plates are permitted on any box, but metallic faceplates, where used, must be grounded (bonded) to an effective ground-fault current path in accordance with [250.4(A)(3)]. See (A). Mike Holt Enterprises, Inc NEC.Code 140

3 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules Figure Wiring to be Accessible Figure Boxes, conduit bodies, and handhole enclosures must be installed so that the wiring is accessible without removing any part of the building, sidewalks, paving, or earth. Figure Exception: Listed boxes and handhole enclosures can be buried if covered by gravel, light aggregate, or noncohesive granulated soil, and their location is effectively identified and accessible for excavation. Mike Holt Enterprises, Inc NEC.Code 141

4 Article 320 Introduction Armored cable is an assembly of insulated conductors, 14 AWG through 1 AWG, that are individually wrapped within waxed paper. The conductors are contained within a flexible spiral metal (steel or aluminum) sheath that interlocks at the edges. AC cable has an outside appearance like flexible metal conduit. Many electricians call this metal cable BX Uses Permitted Type AC cable is permitted only where not subject to physical damage in the following locations, and in other locations and conditions not prohibited by or elsewhere in the Code: (1) Exposed and concealed, (2) Cable trays, (3) Dry locations, (4) Embedded in plaster or brick, except in damp or wet locations, and (5) Air voids where not exposed to excessive moisture or dampness Uses Not Permitted Type AC cable cannot be installed in the following locations: (1) In theaters and similar locations, except as permitted by 518.4(A), (2) In motion picture studios, (3) In any hazardous (classified) location, except as permitted by (B)(3), (B)(3), and , (4) Where exposed to corrosive fumes or vapors, (5) Embedded in plaster finish on brick or other masonry in damp or wet locations. Author s Comment: Type AC cable is permitted in other environmental air spaces [300.22(C)(1)]. Mike Holt Enterprises, Inc NEC.Code 142

5 Article 330 Introduction Metal-clad cable encloses one or more insulated conductors in a metal sheath of either corrugated or smooth copper or aluminum tubing, or spiral interlocked steel or aluminum. The physical characteristics of MC cable make it a versatile wiring method that can be used in almost any location and for almost any application. The most common type of MC cable is the interlocking type, which looks similar to armored cable or flexible metal conduit Uses Permitted (A) General Uses. Type MC cable is permitted only where not subject to physical damage, and in other locations and conditions not prohibited by , or elsewhere in the Code: (1) In branch circuits, feeders and services. (2) In power, lighting, control, and signal circuits. (3) Indoors or outdoors. (4) Exposed or concealed. (5) Directly buried (if identified for the purpose). (6) In a cable tray. (7) In a raceway. (8) As aerial cable on a messenger. (9) In hazardous (classified) locations as permitted in (B), (B), and (10) Embedded in plaster or brick. (11) In wet locations, if one or more of the following are met: a. The metallic covering is impervious to moisture. b. A lead sheath or moisture-impervious jacket is provided under the metal covering. c. The insulated conductors under the metallic covering are listed for use in wet locations. (12) Where single-conductor cables are used, all ungrounded conductors and, where used, the grounded neutral conductor must be grouped together to minimize induced voltage on the sheath [300.3(B)]. (B) Specific Uses. Type MC cable can be installed in compliance with Parts II and III of Article 725 and as applicable, and in accordance with (1) through (4). (1) Cable Tray. Type MC cable installed in cable tray must comply with 392.3, 392.4, 392.6, and through (2) Direct Buried. Direct-buried cable must comply with or , as appropriate. (3) Installed as Service-Entrance Cable. Type MC cable is permitted for service entrances, when installed in accordance with (4) Installed Outside of Buildings or as Aerial Cable. Type MC cable installed outside of buildings must comply with the requirements contained in , , and Author s Comment: Type MC cable is permitted in other environmental air spaces [300.22(C)(1)] Uses Not Permitted Type MC cable cannot be used where exposed to the following destructive or corrosive conditions, unless the metallic sheath is suitable for the conditions or is protected by material suitable for the conditions: (1) Subject to physical damage. (2) Direct burial in the earth, if not identified for this purpose [330.10(A)(5)]. (3) In concrete. FPN: Type MC cable identified for direct burial is suitable for installation in concrete. (4) Where subject to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids. Mike Holt Enterprises, Inc NEC.Code 143

6 Article 334 Introduction Nonmetallic-sheathed cable is a wiring type enclosing two or three insulated conductors, 14 AWG through 2 AWG, within a nonmetallic outer cover. Because this cable is nonmetallic, it contains a separate equipment grounding conductor.nm cable is a common wiring method used for residential and commercial branch circuits. Many electricians call this wiring Romex Uses Permitted Type NM and Type NMC cables can be used in the following: (1) One- and two-family dwellings. Figure Figure (3) Other structures permitted to be of Types III, IV, and V construction, except as prohibited in Cables must be concealed within walls, floors, or ceilings that provide a thermal barrier of material with at least a 15-minute finish rating as identified in listings of fire-rated assemblies. Figure Figure Figure (2) Multifamily dwellings permitted to be of Types III, IV, and V construction. Figure Author s Comment: See Article 100 for the definition of Concealed. Mike Holt Enterprises, Inc NEC.Code 144

7 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules FPN No. 1: Building constructions are defined in NFPA 220, Standard on Types of Building Construction, the applicable building code, or both. FPN No. 2: See Annex E for determination of building types [NFPA 220, Table 3-1]. (4) Cable trays, where the cables are identified for this use. FPN: See for temperature limitation of conductors Uses Not Permitted (A) Types NM and NMC. (1) In any dwelling or structure not specifically permitted in (1), (2), and (3). (2) Exposed in dropped or suspended ceilings in other than one- and two-family and multifamily dwellings. Figure (3) As service-entrance cable. (4) In commercial garages having hazardous (classified) locations as defined in (5) In theaters and similar locations, except where permitted in 518.4(B). (6) In motion picture studios. (7) In storage battery rooms. (8) In hoistways or on elevators or escalators. (9) Embedded in poured cement, concrete, or aggregate. (10) In hazardous (classified) locations, except where permitted by the following: a (B)(3) b (B)(3) c (B) Type NM. Type NM cables cannot be used under the following conditions or in the following locations: (1) Where exposed to corrosive fumes or vapors. (2) Where embedded in masonry, concrete, adobe, fill, or plaster. (3) In a shallow chase in masonry, concrete, or adobe and covered with plaster, adobe, or similar finish. (4) Where subject or exposed to excessive moisture or dampness. Author s Comment: Type NM cable isn t permitted in ducts, plenums, or other environmental air spaces [300.22] or for wiring in patient care areas [517.13]. Figure Mike Holt Enterprises, Inc NEC.Code 145

8 Article 338 Introduction Service-entrance cable can be a single conductor or multiconductor assembly with an overall covering. This cable is used primarily for services not over 600V, but can also be used for feeders and branch circuits Uses Permitted (A) Service-Entrance Conductors. Service-entrance cable used as service-entrance conductors must be installed in accordance with Article 230. Type USE used for underground service laterals can emerge from the ground if protected in accordance with 300.5(D). (B) Branch Circuits or Feeders. (1) Insulated Conductors. Type SE cable is permitted in wiring systems where all of the circuit conductors of the cable are of the rubber-covered or thermoplastic type. (2) Uninsulated Conductor. Type SE cable is permitted for use where the insulated conductors are used for circuit wiring and the uninsulated conductor is only used for equipment grounding (bonding). Figure Exception: The uninsulated conductor can be used for the grounded neutral conductors when in compliance with , , and through Author s Comment: USE cable cannot be used for interior wiring because it doesn t have flame-retardant insulation. (3) Temperature Limitations. Type SE cable used to supply appliances cannot be subjected to conductor temperatures exceeding its insulation rating. (4) Installation Methods for Branch Circuits and Feeders. Type SE cable used for branch circuits or feeders must comply with (a) and (b). (a) Interior Installations. Type SE cable used for interior branch circuit of feeder wiring must be installed in accordance with Parts I and II of Article 334, excluding Author s Comment: This means that when Type SE cables are used for interior branch circuits or feeders, the 60 C ampacity limitation of Type NM cable contained in doesn t apply and the conductors can be sized to the terminal ratings in accordance with (C). Figure Figure Figure Mike Holt Enterprises, Inc NEC.Code 146

9 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules Question: What size Type SE cable is required to supply a 10 kw, 240V single-phase fixed space heater with a 3A blower motor? The terminals are rated 75 C. (a) 2 AWG (b) 4 AWG (c) 6 AWG (d) 8 AWG Answer: (b) 4 AWG Step 1: Step 2: Determine the Total Load in Amperes I = VA/E I = 10,000W/240V + 3A I = 44.67A Size Conductor and Protection. According to 424.3(B), the ungrounded conductors and overcurrent protection device for electric space-heating equipment must be sized no less than 125 percent of the total heating load A x 1.25 = 56A 6 AWG, rated 65A at 75 C would be required with a 60A protection device (b) Exterior Installations. Service-entrance cable used for exterior branch circuits or feeders must be installed in accordance with Article 225. Author s Comment: Type SE cable isn t permitted in ducts, plenums, other environmental air spaces [300.22], or in patient care areas [517.13]. FPN: See for temperature limitation of conductors. Mike Holt Enterprises, Inc NEC.Code 147

10 Article 362 Introduction Electrical nonmetallic tubing is a pliable, corrugated, circular raceway made of polyvinyl chloride (PVC). In some parts of the country, this raceway is called Smurf pipe, because when it originally came out, at the height of popularity of the children s characters the Smurfs, it was available only in blue Uses Not Permitted (1) In hazardous (classified) locations, except as permitted by and (A)(1). (2) For the support of luminaires or equipment. See (3) Where the ambient temperature exceeds 50 C (122 F). (4) To contain conductors that operate at a temperature above the temperature rating of the raceway. Figure (6) As a wiring method for systems over 600V. (7) Exposed in buildings over three floors, except as permitted by (2) and (5) Ex. (8) In assembly occupancies or theaters, except as permitted by and (9) Exposed to the direct rays of the sun for an extended period, unless listed as sunlight resistant. Author s Comment: Exposing electrical nonmetallic tubing to direct rays of the sun for an extended time may result in the product becoming brittle, unless listed to resist the effects of ultraviolet (UV) radiation. Figure Figure Figure Exception: Conductors rated at a temperature above the electrical nonmetallic tubing temperature rating are permitted, provided the conductors do not operate at a temperature above the electrical nonmetallic tubing listed temperature rating. (5) For direct earth burial. Author s Comment: Electrical nonmetallic tubing can be encased in concrete [362.10(6)]. (10) Where subject to physical damage. Author s Comment: Electrical nonmetallic tubing is prohibited as a wiring method in ducts, plenums, and other environmental air handling spaces [300.22] and for patient care area circuits in health care facilities [517.13(A)]. Mike Holt Enterprises, Inc NEC.Code 148

11 Article 376 Introduction A metal wireway is a sheet metal trough with hinged or removable covers. Conductors and cables are placed in it after the wireway has been installed as a complete system.rule Uses Not Permitted. (1) Subject to severe physical damage. (2) Subject to corrosive environments. Mike Holt Enterprises, Inc NEC.Code 149

12 Article 404 Introduction The requirements of Article 404 apply to switches of all types, such as snap (toggle) switches, dimmers, fan switches, knife switches, circuit breakers used as switches, and automatic switches such as time clocks and timers, including switches and circuit breakers used for disconnecting means Switch Cover Plates (Faceplate) (A) Mounting. Faceplates for switches must be installed so that they completely cover the outlet box opening, and where flush mounted, the faceplate must seat against the wall surface. (B) Grounding (Bonding). The metal mounting yokes for switches, dimmers, and similar control switches, must be grounded (bonded) to an effective ground-fault current path, whether or not a metal faceplate is installed. The metal mounting yoke must be grounded (bonded) by one of the following means: Figure (1) Mounting Screw. The switch is mounted with metal screws to a metal box. Figure Author s Comment: Direct metal-to-metal contact between the device yoke of a switch and the box isn t required. (2) Equipment Bonding Conductor. An equipment grounding (bonding) conductor, or equipment bonding jumper is connected to the grounding terminal of the metal mounting yoke. Figure Exception: The metal mounting yoke of a replacement switch isn t required to be bonded to an effective ground-fault current path at an existing installation where no bonding means exists in the outlet box, but only if the switch faceplate is nonmetallic or the replacement switch is GFCI protected. Figure Mike Holt Enterprises, Inc NEC.Code 150

13 Article 406 Introduction This Article contains requirements for the rating, type, and installation of receptacles, cord connectors, and attachment plugs (cord caps) Receptacles in Damp or Wet Locations (A) Damp Locations. Receptacles installed outdoors under roofed open porches, canopies, marquees, and the like, and not subject to beating rain or water runoff or in other damp locations, must be installed in an enclosure that is weatherproof when the attachment plug cap isn t inserted and receptacle covers are closed. Figure (B) Receptacles in Wet Locations. (1) 15 and 20A Receptacles. All 15 and 20A, 125V and 250V receptacles installed in a wet location must be within an enclosure that is weatherproof even when an attachment plug is inserted. Figures and Figure Figure A receptacle installed within an enclosure that is weatherproof when an attachment plug is inserted is also suitable for a damp location. Author s Comment: See Article 100 for the definition of Location, Damp. Figure Mike Holt Enterprises, Inc NEC.Code 151

14 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules (2) Other Receptacles. Receptacles rated other than 15 or 20A, 125V and 250V installed in a wet location must comply with (a) or (b): (a) Wet Location Cover. A receptacle installed in a wet location, where the load isn t attended while in use, must have an enclosure that is weatherproof with the attachment plug cap inserted or removed. (b) Damp Location Cover. A receptacle installed in a wet location for use with portable tools can have an enclosure that is weatherproof when the attachment plug is removed. (C) Bathtub and Shower Space. Receptacles must not be installed within or directly over a bathtub or shower stall. Figure Author s Comment: Receptacles must be located no less than 5 ft from any spas or hot tubs [680.22(A)(1) and (A)(1)]. Hydromassage bathtubs are treated like bathtubs [680.70]. Figure (E) Flush Mounting with Faceplate. The enclosure for a receptacle installed in an outlet box that is flush-mounted on a finished surface must be made weatherproof by a weatherproof faceplate that provides a watertight connection between the plate and the finished surface. Mike Holt Enterprises, Inc NEC.Code 152

15 Article 408 introduction This Article contains requirements for switchboards, panelboards, and distribution boards that control light and power circuits Circuit Directory or Circuit Identification Unused Openings Unused openings for circuit breakers and switches must be closed using identified closures, or other means approved by the authority having jurisdiction, that provide protection substantially equivalent to the wall of the enclosure. Figure All circuits and circuit modifications must be legibly identified as to their clear, evident, and specific purpose. The identification must include sufficient detail to allow each circuit to be distinguished from all others, and the identification must be on a circuit directory located on the face or inside of the door of a panelboard. See Figure Figure Figure Mike Holt Enterprises, Inc NEC.Code 153

16 Article 422 Introduction This Article contains requirements for electric appliances used in any occupancy Permanently Connected Appliance Disconnect (A) Appliance Rated at Not Over 300 VA or 1 8 Horsepower. The branch-circuit overcurrent device, such as a plug fuse or circuit breaker, can serve as the appliance disconnect. (B) Appliance Rated Over 300 VA or 1 8 Horsepower. A switch or circuit breaker located within sight from the appliance can serve as the appliance disconnecting means. If the switch or circuit breaker is capable of being locked in the open position, it does not need to be within sight if the provision for locking or adding a lock is on the disconnecting means. Figure Cord-and-Plug Connected Appliance Disconnect (A) Attachment Plug and Receptacle. An accessible plug and receptacle can serve as the disconnecting means for a cordand-plug connected appliance. Figure (B) Cord-and-Plug Connected Range. The plug and receptacle of a cord-and-plug connected household electric range can serve as the range disconnecting means if the plug is accessible from the front of the range by the removal of a drawer. Figure Figure Figure Author s Comment: Within sight is visible and not more than 50 ft from one to the other [Article 100]. Figure Mike Holt Enterprises, Inc NEC.Code 154

17 Article 430 Introduction This is the motor Article. It contains the specific rules for motor installations, addressing such issues as conductor sizing, overcurrent protection, control circuit conductors, motor controllers, and disconnecting means. Installation requirements for motor control centers are covered in , and air-conditioning and refrigerating equipment are covered in Article Table FLC Versus Motor Nameplate Current Rating (A) General Requirements. (1) Table Full-Load Current (FLC). The motor full-load current ratings listed in Tables , , and are used to determine the conductor ampacity [430.22], the branch-circuit short-circuit and ground-fault protection device size [ and 62], and the ampere rating of disconnecting switches [ ]. Author s Comment: The actual current rating on the motor nameplate full-load amperes (FLA) [430.6(A)(2)] is not permitted to be used to determine the conductor ampacity, the branchcircuit short-circuit and ground-fault protection device size, nor the ampere rating of disconnecting switches. Figure Motors built to operate at less than 1,200 RPM or that have high torques may have higher full-load currents, and multispeed motors will have full-load current varying with speed, in which case the nameplate current ratings must be used. Exception 3: For a listed motor-operated appliance, the motor full-load current marked on the nameplate of the appliance must be used instead of the horsepower rating on the appliance nameplate to determine the ampacity or rating of the disconnecting means, the branch-circuit conductors, the controller, and the branch-circuit short-circuit and ground-fault protection. (2) Motor Nameplate Current Rating (FLA). Overload devices must be sized based on the motor nameplate current rating in accordance with Author s Comment: The motor nameplate full-load ampere rating is identified as full-load amperes (FLA). The FLA rating is the current in amperes that the motor draws while producing its rated horsepower load at its rated voltage, based on its rated efficiency and power factor. Figure Figure Figure Mike Holt Enterprises, Inc NEC.Code 155

18 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules The actual current drawn by the motor depends upon the load on the motor and on the actual operating voltage at the motor terminals. That is, if the load increases, the current also increases, or if the motor operates at a voltage below its nameplate rating, the operating current will increase. Caution: To prevent damage to motor windings from excessive heat (caused by excessive current), never load a motor above its horsepower rating and/or be sure the voltage source matches the motor s voltage rating Single Motor Conductor Size (A) Conductor Size. Conductors to a single motor must be sized not smaller than 125 percent of the motor FLC rating as listed in: Figure Figure Note: The branch-circuit short-circuit and ground-fault protection device using an inverse-time breaker is sized at: 22A x 2.5 = 55A, next size up = 60A [240.6(A) and (C)(1) Exception 1] Branch-Circuit Short-Circuit and Ground-Fault Protection (A) General. The motor branch-circuit short-circuit and ground-fault protective device must comply with (B) and (C). Figure (B) All Motors. A motor branch-circuit short-circuit and ground-fault protective device must be capable of carrying the motor s starting current. (C) Rating or Setting. Table Direct Current Motors Table Single-Phase Motors Table Three-phase motors Question: What size branch-circuit conductor is required for a hp, 230V three-phase motor? Figure (a) 14 AWG (c) 10 AWG Answer: (c) 10 AWG (b) 12 AWG (d) none of these Motor FLC = 22A [Table ] Conductor s Size = 22A x 1.25 Conductor s Size = 27.5A, 10 AWG, rated 30A at 75 C [Table ] (1) Table Each motor branch circuit must be protected against short circuit and ground faults by a protection device sized no greater than the following percentages listed in Table Table Circuit Nontime Dual-Element Inverse- Motor Type Delay Fuse Time Breaker Wound Rotor 150% 150% 150% Direct Current 150% 150% 150% All Other Motors 300% 175% 250% Mike Holt Enterprises, Inc NEC.Code 156

19 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules Question: What size conductor and inverse-time circuit breaker are required for a 2 hp, 230V single-phase motor? Figure (a) 14 AWG, 30A breaker (c) 14 AWG, 40A breaker (b) 14 AWG, 35A breaker (d) none of these Question: What size conductor and inverse-time circuit breaker are required for a hp, 230V three-phase motor? Figure (a) 10 AWG, 50A breaker (c) a or b (b) 10 AWG, 60A breaker (d) none of these Figure Figure Answer: (a) 14 AWG, 30A breaker Step 1. Step 2. Branch-Circuit Conductor [Table , (A), and Table ] 12A x 1.25 = 15A, 14 AWG, rated 20A at 75 C [Table ] Branch-Circuit Protection [240.6(A), (C)(1), and Table ] 12A x 2.5 = 30A Author s Comment: I know it bothers many in the electrical industry to see a 14 AWG conductor protected by a 30A circuit breaker, but branch-circuit conductors are protected against overloads sized between 115 and 125 percent of the motor nameplate current rating [430.32]. See 240.4(A) and 240.4(G) for details. Exception 1: Where the motor short-circuit and ground-fault protection device values derived from Table don t correspond with the standard overcurrent device ratings listed in 240.6(A), the next higher protection device rating can be used. Answer. (c) 10 AWG, 50 or 60A breaker Step 1. Branch-Circuit Conductor [Table , (A), and Table ] 22A x 1.25 = 27.5A, 10 AWG, rated 30A at 75 C [Table ] Step 2. Branch-Circuit Protection [240.6(A), (C)(1) Exception 1, and Table ] 22A x 2.5 = 55A, next size up = 60A Disconnect for Control Circuit (A) Control Circuit Disconnect. Motor control circuit conductors must have a disconnecting means that opens all sources of supply when the disconnecting means is in the open position. If the control circuit conductors are tapped from the controller disconnect, the controller disconnecting means can serve as the disconnecting means for the control circuit conductors [ (A)]. If the control circuit conductors aren t tapped from the controller disconnect, a separate disconnecting means is required for the control circuit conductors, and it must be located adjacent to the controller disconnect. Figure Mike Holt Enterprises, Inc NEC.Code 157

20 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules The controller disconnecting means must simultaneously open all ungrounded conductors of the circuit [ ]. Figure Figure Figure Disconnect Requirement (A) Controller Disconnect. A disconnecting means is required for each motor controller and it must be located within sight from the controller. Figure Author s Comment: The controller disconnecting means can serve as the disconnecting means for the motor control circuit conductors [430.74], as well as for the motor [ (B)]. (B) Motor Disconnect. A disconnecting means is required for each motor and it must be located in sight from the motor location and the driven machinery location. Figure Figure Figure Author s Comment: Within sight is visible and not more than 50 ft from each other [Article 100]. Mike Holt Enterprises, Inc NEC.Code 158

21 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules Exception: A motor disconnecting means isn t required to be within sight from the motor under either condition (a) or (b), if the controller disconnecting means [ (A)] is capable of being locked in the open position and the provision for locking or adding a lock is permanently installed on the controller disconnect. Figure (a) Where locating the disconnecting means is impracticable or introduces additional or increased hazards to persons or property. (b) In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons will service the equipment. Author s Comment: See Article 100 for the definition of Within Sight. FPN 2: For information on lockout/tagout procedures, see NFPA 70E, Standard for Electrical Safety in the Workplace. Figure Mike Holt Enterprises, Inc NEC.Code 159

22 Article 440 introduction This Article applies to electrically driven air-conditioning and refrigeration equipment that has a hermetic refrigerant motor-compressor. The rules in this Article are in addition to, or amend, the rules in Article 430 and other Articles Short-Circuit and Ground-Fault Protection Device Size Short-circuit and ground-fault protection for air-conditioning and refrigeration equipment must be sized no larger than identified on the equipment s nameplate. Figure (A) One Motor-Compressor. The short-circuit and groundfault protection device must not be greater than 175 percent of the motor-compressor current rating. If the protection device sized at 175 percent isn t capable of carrying the starting current of the motor-compressor, the next size larger protection device can be used, but in no case can it exceed 225 percent of the motor-compressor current rating. Question: What size conductor and protection is required for a 24A motorcompressor connected to a 240V circuit? Figure (a) 10 AWG, 40A (c) a or b (b) 10 AWG, 60A (d) none of these Figure Answer: (a) 10 AWG, 40A Figure If the equipment doesn t have a nameplate specifying the size and type of protection device, then the protection device must be sized in accordance with (A) or (B). Step 1. Branch-Circuit Conductor [Table and ] 24A x 1.25 = 30A, 10 AWG, rated 30A at 75 C [Table ] Step 2. Branch-Circuit Protection [240.6(A) and (A)] 24A x 1.75 = 42A, next size down = 40A If the 40A protection device isn t capable of carrying the starting current, then the protection device can be sized up to 225 percent of the equipment load current rating. 24A x 2.25 = 54A, next size down 50A (B) Rating for Equipment. Where the equipment incorporates more than one hermetic refrigerant motor-compressor, or a hermetic refrigerant motor-compressor and other motors Mike Holt Enterprises, Inc NEC.Code 160

23 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules or other loads, the equipment short-circuit and ground-fault protection must be sized as follows: (1) Motor-Compressor Largest Load. The rating of the branch-circuit short-circuit and ground-fault protective device must not be greater than the largest motor-compressor short-circuit ground-fault protection device, plus the sum of the rated-load currents of the other compressors. Author s Comment: The branch-circuit conductors are sized at 125 percent of the larger motor-compressor current, plus the sum of the rated-load currents of the other compressors [440.33] Conductor Size One Motor-Compressor If equipment doesn t have a nameplate identifying the minimum circuit ampacity, the branch-circuit conductors to a single motor-compressor must have an ampacity not less than 125 percent of the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater. Author s Comments: In accordance with (A), branch-circuit conductors must have branch-circuit protection sized between 175 percent and 225 percent of the rated-load current to provide protection against short circuits and ground faults. In accordance with (A), branch-circuit conductors must have branch-circuit protection sized between 175 percent and 225 percent of the rated-load current to provide protection against short circuits and ground faults. Question: What size conductor and protection device is required for an 18A motor compressor? Figure (a) 12 AWG, 30A (c) a or b (b) 10 AWG, 50A (d) none of these Figure Answer: (a) 12 AWG, 30A Step 1: Branch-Circuit Conductor [Table and ] 18A x 1.25 = 22.5A, 12 AWG, rated 25A at 75 C [Table ] Step 2.: Branch-Circuit Protection [240.6(A) and (A)] 18A x 1.75 = 31.5A, next size down = 30A If the 30A protection device isn t capable of carrying the starting current, then the protection device can be sized up to 225 percent of the equipment load current rating. 18A x 2.25 = 40.5A, next size down 40A Author s Comment: A 30A or 40A protection device is permitted to protect a 12 AWG conductor. See 240.4(A) and 240.4(G) for details. Mike Holt Enterprises, Inc NEC.Code 161

24 Article 450 Introduction This Article contains requirements for the installation of all transformers Overcurrent Protection Overcurrent protection of the primary winding of a transformer not exceeding 600V must comply with (B). FPN 2: 4-wire three-phase 120/208V or 277/480V systems that supply nonlinear line-to-neutral loads can overheat because of triplen harmonic currents (3rd, 9th, 15th, 21st, etc.) [450.9 FPN 2]. Figure Table 450.3(B) Primary Protection only Primary Current Rating Maximum Protection 9A or More 125%, see Note 1 Less Than 9A 167% Less Than 2A 300% Note 1. Where 125 percent of the primary current doesn t correspond to a standard rating of a fuse or nonadjustable circuit breaker, the next higher rating is permitted [240.6(A)]. Question: What is the primary protection device rating and conductor size required for a 45 kva, three-phase, 480V 120/208V transformer that is fully loaded? Terminals are rated 75 C. Figure (a) 8 AWG, 40A (c) 6 AWG, 60A (b) 6 AWG, 50A (d) 4 AWG, 70A Figure Author s Comment: For more information on this subject, visit (B) Overcurrent Protection for Transformers Not Over 600V. The primary winding of a transformer must be protected against overcurrent in accordance with the percentages listed in Table 450.3(B) and all applicable notes. Figure Mike Holt Enterprises, Inc NEC.Code 162

25 Top 101 Rules of Understanding the NEC, Volume 1 Part 4: Rules Answer: (d) 70A Step 1: Step 2: Step 3: Step 4: Primary current I = VA/(E x 1.732) I = 45,000 VA/(480V x 1.732) I = 54A The primary protection device rating [240.6(A)] 54A x 1.25 = 68A, next size up 70A, Note 1 The primary conductor must be sized to carry 54A continuously (54A x 1.25 = 68A) [215.2(A)(1)] and be protected by a 70A protection device [240.4(A)]. A 4 AWG conductor rated 85A at 75 C meets all of the requirements [110.14(C)(1) and ]. Secondary current I = VA/(E x 1.732) I = 45,000 VA/ (208V x 1.732), = 125A Author s Comment: Secondary conductors having a maximum length of 25 ft that terminate in an overcurrent protection device that doesn t exceed the ampacity of the conductors, must be sized at 125 percent of the continuous load [215.2(A)(1) and (C)(6)]. Question: What is the secondary conductor size required for a 45 kva, three-phase, 480V 120/208V transformer, that supplies a 200A lighting and appliance panelboard that is fully loaded? Terminals are rated 75 C. Figure (a) 1 AWG (b) 1/0 AWG (c) 2/0 AWG (d) 3/0 AWG Answer: (c) 2/0 AWG Step 1: Secondary current I = VA/(E x 1.732) I = 45,000 VA/(208V x 1.732) I = 125A Figure Step 2: Secondary conductors must be sized to 125 percent of the continuous load [215.2(A)(1)]. 125A x 1.25 = 156A, 2/0 AWG rated 175A at 75 C termination Secondary conductors must terminate in an overcurrent protection device that doesn t exceed the ampacity of the conductors [240.21(C)(6)]. 2/0 AWG, rated 175A at 75 C, terminating on a 175A protection device meets this requirement. Mike Holt Enterprises, Inc NEC.Code 163