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GOALS: • understand the Code requirements for bathrooms receptacles. • understand the Code requirements for making load calculations and electrical connections for electric dryers. • understand the Code requirements for receptacle outlets in laundry areas. • understand the principles of exhaust fans. • understand the Code requirements for attic wiring. TABLE 1 Laundry-Rear Entrance-Powder Room-Attic (Circuit B10). Description: Rear Entry hall receptacle Powder Room vanity luminaire Rear Entrance hall ceiling luminaires @ 100 W each Laundry Room fluorescent luminaire Four 32-W lamps Attic luminaires @ 75 W each Laundry exhaust fan Powder Room exhaust fan LIGHTING CIRCUIT B10 The estimated loads for the various receptacles and luminaires in the Laundry, Rear Entry, Powder Room, and Attic are shown in TBL. 1. The lighting circuit is discussed a little later on in this section. RECEPTACLE CIRCUIT B21 Receptacles in a residential bathroom require special treatment. This is discussed in detail in Section 3. Now would be a good time for you to review Section 3. Circuit B21 is a separate 20-ampere branch circuit that supplies the receptacle in the Powder Room. A bathroom is defined in Article 100 as An area that has a basin, plus one or more of the following: a toilet, a urinal, a tub, a shower, a bidet, or similar plumbing fixtures.* Therefore, by definition, the NEC considers the powder room to be a bathroom. As a result, special requirements apply to the receptacle outlet in the room. CLOTHES DRYER CIRCUIT D The electric clothes dryer requires a separate 20/240-volt, single-phase, 3-wire branch circuit. In this residence, the electric clothes dryer is indicated on the Electrical Plans in the laundry by the symbol D. It is supplied by Circuit B(1-3) located in Panel B. Ill. 1 shows the internal components and wiring of a typical electric clothes dryer. Dryer Connection Methods Electric clothes dryers can be connected in several ways: One method is to run a 3-wire armored cable directly to a junction box on the dryer provided by the manufacturer, Ill. 2. This flexible connection allows the dryer to be moved for servicing without disconnecting the wiring. The armor of the Type AC cable serves as the equipment grounding conductor. If Type AC cable is used for the branch circuit wiring, the disconnecting means must comply with NEC 422.32 as covered later in this section. Another method is to run a conduit (EMT) to a point just behind the dryer. A combination coupling makes the transition from the EMT to a length of flexible metal conduit 2 ft (600 mm) to 3 ft (900 mm) long, as in Ill. 3. This flexible connection also allows the dryer to be moved for servicing without disconnecting the wiring. A separate equipment grounding conductor must be installed in the EMT to meet the grounding requirements found in 250.118(5). If the wiring method described in this paragraph is used for the branch circuit wiring, the disconnecting means must comply with NEC 422.32 as covered later in this section. Probably the most common method is to install a 4-wire, 30-ampere receptacle on the wall behind the dryer. A 4-wire, 30-ampere cord ("pigtail") is then connected to the dryer. This arrangement is referred to as a "cord-and-plug connection" and is shown in Ill. 4. In conformance to 210.23, the connected load shall not exceed the branch-circuit rating. ILL. 1 Clothes dryer: typical wiring and components. Equipment grounding conductor Grounding strap must be connected to neutral if equipment grounding conductor isn't supplied with branch circuit. ILL. 2 Dryer connected by armored cable. ILL. 3 Dryer connected by EMT and flexible metal conduit. ILL. 4 Dryer connection using a cord set. Appliances All new homes have appliances-some that operate entirely on electricity and some that require electricity as well as another energy source, such as a gas furnace. Article 422 in the NEC is where to look for the majority of Code requirements for appliances. In Article 422, you will find quite a few references to other parts of the NEC, such as Article 430 where motors are involved, and Article 440 where hermetic motor compressors (air conditioners and heat pumps) are involved. As you continue studying this text, specific Code rules for appliances are discussed at the time it becomes necessary to mention the rule. Disconnecting Means All electrical appliances are required to have a disconnecting means, 422.30. For permanently connected motor-driven appliances, 422.32 states that a disconnect switch or a circuit breaker in a panelboard may serve as the disconnecting means, provided the switch or circuit breaker is within sight of the appliance, or is capable of being locked in the "Off" position. Breaker manufacturers produce "lock-off" devices that fit over the circuit breaker handle. Disconnect switches have provisions for locking the switch "Off." The "unit switch" on an appliance is acceptable as a disconnect for an appliance, provided the unit switch has a marked "Off" position and it disconnects all the conductors in the appliance; 422.34. This does not normally apply to controllers of the type typically provided in dishwashers as they don't shut off all the power to the appliance. If the appliance does have a qualifying unit switch, the service disconnect serving as the "other" disconnect does not have to be within sight of the appliance, 422.32, Exception. Cord-and-Plug Connection. For cord-and-plug connected appliances, 422.33(A) accepts the cord and -plug arrangement as the disconnecting means. Ill. 4 shows a 30-ampere, 4-wire receptacle configuration for an electric clothes dryer installation in conformance to the latest NEC. Ill. 5 shows (A) a surface-mount 4-wire receptacle and (B) a flush mount 4-wire receptacle. For most residential electric clothes dryers, receptacles and cord sets are rated 30 amperes, 125/250 volts. Some large electric clothes dryers might require a 50-ampere, 125/250-volt receptacle and cord set. Receptacles for dryers can be surface mounted or flush mounted. Flush-mounted receptacles are quite large and require a large wall box. A 4-in. square, 2 1/8-in. deep outlet box with a suitable two gang plaster ring generally works fine. Correct box sizing is determined by referring to TBL. 314.16(A) or TBL. 314.16(B), or to Ill. 2-20 and TBL. 2-1. To avoid duplication of text, refer to Section 20 for a complete description of ratings and blade and slot configurations for 3-wire and 4-wire dryer and range receptacles and their associated cord sets. Load Calculations In this residence, the dryer is installed in the Laundry Room. The Schedule of Special Purpose Outlets in the specifications shows that the dryer is rated 5700 watts, 120/240 volts. The schematic wiring diagram in Ill. 1 shows that the heating element is connected across 240 volts. The motor and lamp are connected to the 120-volt terminals. It is impossible for the electrician to know the ampere rating of the motor, the heating elements, timers, lights, relays, and so on, and in what sequence they actually operate. This dilemma is answered in the NEC and UL listing requirements for all appliances. The nameplate must show volts and amperes or volts and watts, 422.60(A). The nameplate must also show the minimum supply circuit conductor's ampacity and the maximum overcurrent protection, 422.62(B)(1). A minimum load of 5000 watts (volt-amperes) or the nameplate rating of the dryer, whichever is larger, is used when calculating branch circuit, feeder, or service-entrance requirements, 220.54. The rating of an appliance branch circuit must not be less than the marked rating on the appliance, 422.10(A). The electric clothes dryer in this residence has a nameplate rating of 5700 watts. This calculates out to be: I=W/E = 23.75 amperes A Surface outlet; B Flush outlet ILL. 5 (A) shows a surface-mount 4-wire receptacle. (B) shows a flush-mount 4-wire receptacle. These are typically rated 30 amperes and are of the types required to supply electric dryers. Prior to the 1996 NEC, 3-wire receptacles and cords were permitted. This is no longer permitted. It is mandatory that a separate equipment grounding conductor be installed to ground the frames of electric clothes dryers and electric ranges. Also see Ill. 20-2. Because wiring devices used for dryer circuits are rated at 30 amperes and to comply with 210.3, we have a minimum 30-ampere branch-circuit rating requirement. Conductor Sizing The minimum branch-circuit rating for the electric clothes dryer was found to be 30 amperes, and that's the minimum rating of the overcurrent protective device-fuses or circuit breaker. We need to find a conductor that has an ampacity of 30 amperes that will serve as the branch circuit for the dryer. The conductors will be protected by the 30-ampere overcurrent device. According to TBL. 310.15(B)(16), the allow able ampacity for a 10 AWG copper conductor is 30 amperes in the 60°C column. The maximum overcurrent protection for these conductors must not exceed 30 amperes, 240.4(D). In this residence, Circuit B(1-3) is a 3-wire, 30-ampere, 240-volt branch circuit. Nonmetallic-sheathed cable is run concealed in the walls from Panel B to a flush-mounted 4-in. square box behind the dryer location in the Laundry Room. The nonmetallic-sheathed cable contains three 10 AWG conductors plus a 10 AWG equipment grounding conductor. Where EMT is used as the wiring method, TBL. C1, Annex C of the NEC shows that three 10 AWG THHN conductors require trade size 1/2 EMT. The EMT serves as the equipment ground per 250.118(4). Overcurrent Protection for the Dryer The motor of the dryer has integral thermal overload protection as required by 422.11(G). Note the motor protector in Ill. 1. This protection is required by UL standards and prevents the motor from reaching dangerous temperatures as the result of an overload, bearing failure, or failure to start. Also note the temperature safety switch. This is a high-temperature cutoff that shuts off the heating element should the appliance's thermostat fail to operate. This high temperature cutoff is also a UL requirement. Overcurrent Protection for Branch Circuit NEC 422.62 requires the appliance to be marked with the minimum supply circuit conductor ampacity and the maximum size overcurrent device. The rating of the branch circuit must not be less than the rating marked on the appliance, 422.10(A). In 422.11(A), we find that the overcurrent protection for the branch-circuit conductors must be sized according to 240.4, which refers us right back to Article 422-Appliances. The maximum overcurrent protection for 10 AWG copper conductors is 30 amperes, 240.4(D). Grounding Frames of Electric Dryers and Electric Ranges For protection against electrical shock hazard, frames of electric clothes dryers and electric ranges must be grounded. Some key Code references are 250.134, 250.138, 250.140, and 250.142(B). There are now two methods for grounding the frames of electric dryers and electric ranges, namely New Installations and Existing Installations. New Installations. One accepted grounding means is to connect the appliance with a metal raceway such as EMT, an equipment grounding conductor installed through flexible metal conduit ( Greenfield), armored cable (BX), or other means listed in 250.118. There are limitations on the use of flexible metal conduit as an equipment grounding conductor. See 250.118(5) and 348.60. This topic is covered in Section 4. The separate equipment grounding conductor found in nonmetallic-sheathed cable is also an acceptable equipment grounding means. The equipment grounding conductor in nonmetallic-sheathed cable is sized according to TBL. 250.122. See Ill. 6. Service-entrance cable is also permitted as a branch circuit to an electric dryer or electric range. The Code rules governing service-entrance cable are covered in Section 4. When electric clothes dryers and electric ranges are cord-and-plug connected, the receptacle and the cord set must be 4-wire, the fourth wire being the separate equipment grounding conductor. The small copper bonding strap (link) that's furnished with an electric clothes dryer or electric range must not be connected between the neutral terminal and the metal frame of the appliance. Existing Installations. Prior to the 1996 edition of the NEC, 250.60 permitted the frames of electric ranges, wall-mounted ovens, surface cooking units, and clothes dryers to be grounded to the neutral conductor, as in Ill. 7. By way of Tentative Interim Amendment 53, this special permission was put into effect in July of 1942, and was supposedly an effort to conserve raw materials during World War II. In effect, this special permission allowed the neutral conductor to serve a dual purpose: (1) the neutral conductor and (2) the equipment grounding conductor. This special permission remained in effect until the 1996 NEC. Since then, grounding equipment such as ranges and dryers to a neutral conductor isn't permitted! Existing installations need not be changed, if they were in conformance to the NEC at the time the branch circuit was installed. If an electric clothes dryer or electric range is to be installed in a residence where the dryer branch circuit wiring had been installed according to pre 1996 NEC rules, the wiring does not have to be changed. Merely use the grounding strap furnished by the dryer manufacturer to make a connection between the neutral conductor and the frame of the dryer. ILL. 7 Prior to the 1996 National Electrical Code, it was permitted to ground the junction box to the neutral conductor only if the box was part of the circuit for electric ranges, wall-mounted ovens, surface cooking units, and clothes dryers. The receptacle was permitted to be a 3-wire type because the appliance grounding was accomplished by making a connection between the neutral conductor and the metal frame of the appliance. This is no longer permitted. Three 10 AWG nonmetallic-sheathed cable. no eq. ground ILL. 6 New installations of branch-circuit wiring for electric ranges, wall-mounted ovens, surface cooking units, and clothes dryers require that all equipment grounding be done according to 250.134, 250.138, 250.140, and 250.142(B). Receptacles and cord sets must be 4-wire (three circuit conductors plus equipment grounding conductor). Three 10 AWG nonmetallic sheathed cable with eq. ground; 30-ampere, 4-wire, 125/250-volt NEMA 14-30R receptacle. RECEPTACLE OUTLETS--LAUNDRY At least one receptacle outlet shall be installed for the laundry equipment, 210.52(F). For this laundry receptacle, a dedicated 20-ampere branch circuit shall be provided to supply the laundry receptacle outlet or outlets. This circuit shall have no other outlets, 210.11(C)(2). In this residence, the clothes washer receptacle is supplied by 20-ampere Circuit B18. This branch circuit is permitted to supply the other receptacle outlets in the room intended for laundry equipment but isn't per mitted to supply the outdoor weatherproof receptacle. All 125-volt, single-phase, and 20-ampere receptacles within 6 ft (1.8 m) of the outside edge of a sink shall be GFCI protected, 210.8(A)(7). There are no exceptions to this rule. Because all three receptacles in the Laundry Room are within 6 ft (1.8 m) of the outside edge of the laundry sink, they are all required to be GFCI protected. As repeated a number of times in this text, GFCI protection can be provided by either a GFCI circuit breaker or a GFCI receptacle. This is covered in detail in Section 6. Ill. 8 shows the cable layout for the Laundry Room. Circuit B20 is an additional 20-ampere branch circuit for the laundry area. It supplies the other two receptacles in the Laundry Room that can be used for plugging in an iron, sewing machine, TV, radio, or other plug-in appliance. This circuit also serves the weatherproof receptacle on the outside wall of the laundry area. This branch circuit is in addition to the required separate 20-ampere circuit (B18) for the laundry equipment. Circuits B18 and B20 are included in the calculations for service-entrance and feeder conductor sizing at a calculated load of 1500 volt-amperes per circuit, 220.52(B). This load is included with the general lighting load for the purpose of calculating the service-entrance and feeder conductor sizing and is subject to the demand factors that are applicable to these calculations. See the complete calculations in Section 29. ILL. 8 Cable layout for Laundry Room receptacles. Depth of Box--Watch Out! Determining the cubic volume of a box isn't the end of the story. Outlet and device boxes have to be deep enough so that conductors will not be damaged when installing the wiring device or equipment into the box. Merely calculating and providing the proper volume of a box isn't always enough. The volume calculation might prove adequate, yet the size (depth) of the wiring device or equipment might be such that conductors behind it may possibly be damaged. See NEC 314.24. Width of Box--Watch Out! Large wiring devices, such as a 30-ampere, 3-pole, 4-wire dryer or range receptacle will not fit into a single gang box that's 2 in. (50.8 mm) wide. Dryer receptacles measure 2.10 in. (53.3 mm) in width. Likewise, a 50-ampere, 3-pole, 4-wire receptacle measures 2.75 in. (69.9 mm) in width. Consider using a 4-in. (101.6-mm) square box with a 2-gang plaster device ring for flush mounting or a 2-gang raised cover for surface mounting. Or, use a 2-gang device box. The center-to-center mounting holes of both the 30-ampere and the 50-ampere receptacles are 1.81 in. (46.0 mm) apart, exactly matching the center-to-center holes of a 2-gang plaster ring, raised cover, or gang device box. See NEC 314.16(B)(4). COMBINATION WASHER/DRYERS Combination washer/dryers take up about half the floor space of a traditional washer and dryer pair. Some models have the washer/dryer units combined into one appliance, using the same drum for both wash and dry cycles. Others stack the dryer above the washer. Electric washer/dryer combinations generally require a 30-ampere branch circuit similar to that required for a typical electric clothes dryer. The receptacle would be a 30-ampere, 4-wire, 125/250-volt, NEMA 14-30R, Ill. 6. Gas washer/dryer combinations draw 10 or 12 amperes and plug into a standard grounding-type receptacle. If the receptacle is located within 6 ft (1.8 m) of the outside edge of a sink, then it must be GFCI protected, 210.8(A)(7). This receptacle and the branch circuit for the laundry appliances must conform to 210.52(F) and 210.11(C)(2). For installations that require a 30-ampere branch circuit and receptacle for a combination washer/ dryer, a 120-volt receptacle and separate 20-ampere branch circuit must still be provided in conformance to 210.52(F) and 210.11(C)(2). LIGHTING CIRCUIT The general lighting circuit for the Laundry, Powder Room, and hall area is supplied by Circuit B10. This circuit must be AFCI protected as required by 210.12(A). Note on the cable layout, Ill. 9, that in order to help balance loads evenly, the attic lights are also connected to Circuit B10. The types of vanity and ceiling luminaires and wall receptacle outlets, as well as the circuitry and switching arrangements, are similar to types discussed in other sections of this text and will not be repeated. The receptacle in the Powder Room is sup plied by Circuit B21, a separate 20-ampere branch circuit as required by 210.52(D), discussed in Section 10. ILL. 9 Cable layout for Laundry, Rear Entrance, Powder Room, and Attic (Circuit B10). ILL. 10 Exhaust fans; WALL TYPE, CEILING TYPE Exhaust Fans Ceiling exhaust fans are installed in the Laundry and in the Powder Room. These exhaust fans are connected to Circuit B10. The exhaust fan in the Laundry will remove excess moisture resulting from the use of the clothes washer, dryer, and ironing. Exhaust fans may be installed in walls or ceilings, as in Ill. 10. The wall-mounted fan can be adjusted to fit the thickness of the wall. If a ceiling-mounted fan is used, sheet-metal duct must be installed between the fan unit and the outside of the house. The fan unit terminates in a metal hood or grille on the exterior of the house. The fan has a shutter that opens as the fan starts up and closes as the fan stops. The fan may have an integral pull-chain switch for starting and stopping, or it may be used with a separate wall switch. In either case, single-speed or multispeed control is available. The fan in use has a very small power demand, 90 volt-amperes. To provide better humidity control, both ceiling mounted and wall-mounted fans may be controlled with a humidistat. This device starts the fan when the humidity reaches a certain value. When the humidity drops to a preset level, the humidistat turns the fan off. Some of the more expensive exhaust fans have a built-in sensor that will automatically turn on the exhaust fan at a predetermined humidity level. The fan will automatically turn off when the humidity has been lowered to a preset level. This eliminates the need for a separate wall-mounted humidity control (humidistat). ILL. 11 Pilot lamp connections. ILL. 12 Example of neon pilot lamp in handle of toggle switch. ATTIC LIGHTING and PILOT LIGHT SWITCHES NEC 210.70(A)(3) requires that at least one lighting outlet must be installed in an attic and that this lighting outlet contain a switch such as a pull-chain lamp-holder, or be controlled by a switch located near the entry to the attic. This section of the Code addresses attics that are used for storage and attics that contain equipment that might need servicing, such as air-conditioning equipment. NEC 210.70(A)(3) requires that the lighting outlet(s) be installed at or near this equipment. A 125-volt, single-phase, or 20-ampere receptacle outlet shall be installed in an accessible location within 25 ft (7.5 m) of air-conditioning or heating equipment in attics, in crawl spaces, or on the roof, 210.63. Connecting this receptacle outlet to the load side of the equipment's disconnecting means isn't permitted because this would mean that if you turned off the equipment, the power to the receptacle would also be off and thus would be use less for servicing the equipment. The residence discussed in this text does not have air-conditioning, heating, or refrigeration equipment in the attic or on the roof. The porcelain lampholders are available with a receptacle outlet for convenience in plugging in an extension cord. However, most electrical inspectors (authority having jurisdiction) would not accept the porcelain lampholder's receptacle in lieu of the required receptacle outlet as stated in 210.63. The four porcelain lampholders in the attic are turned on and off by a single-pole switch on the garage wall close to the attic storable ladder. Associated with this single-pole switch is a pilot light. The pilot light may be located in the handle of the switch or it may be separately mounted. Ill. 11 shows how pilot lamps are connected in circuits containing either single-pole or 3-way switches. Because the attic in this residence is served by a folding storable ladder, switch control in the attic isn't required. Where a permanent stairway of six or more risers is installed, 210.70(A)(2)(c) requires switch control at both levels. If a neon pilot lamp in the handle (toggle) of a switch does not have a separate grounded conductor connection, then it will glow only when the switch is in the "Off" position, as the neon lamp will then be in series with the lamp load, Ill. 12. The voltage across the load lamp is virtually zero, so it does not burn, and the voltage across the neon lamp is 120 volts, allowing it to glow. When the switch is turned on, the neon lamp is bypassed (shunted), causing it to turn off and the lamp load to turn on. Use this type of switch when it's desirable to have a switch glow in the dark to make it easy to locate. ILL. 13 Protection of nonmetallic-sheathed cable or armored cable in an attic. Refer to 334.23 and 320.23. Installation of Cable in Attics When nonmetallic-sheathed cable is installed in accessible attics, the installation must conform to the requirements of 334.23. This section refers the reader directly to 320.23, which describes how the cable is to be protected. See Ills. 13 and 14. In accessible attics, cables must be protected by guard strips if: • they are run across the top of floor joists. • they are run across the face of studs d or rafters e within 7 ft (2.1 m) of the floor or floor joists. Guard strips aren't required if the cable is run along the sides of rafters, studs, or floor joists f. In attics not accessible by permanent stairs or ladders, as in Ill. 13(B), guard strips are required only within 6 ft (1.8 m) of the nearest edge of the scuttle hole or entrance. Ill. 13(C) illustrates a cable installation that most electrical inspectors consider to be safe. Because the cables are installed close to the point where the ceiling joists and the roof rafters meet, they are protected from physical damage. It would be very difficult for a person to crawl into this space or store cartons in an area with such a low clearance. Although the plans for this residence show a 2-ft wide catwalk in the attic, the owner may decide to install additional flooring in the attic to obtain more storage space. Because of the large number of cables required to complete the circuits, it would interfere with flooring to install guard strips wherever the cables run across the tops of the joists, as in Ill. 14. However, the cables can be run through holes bored in the joists and along the sides of the joists and rafters. In this way, the cables don't interfere with the flooring. When running cables parallel to framing members or furring strips, be careful to maintain at least 1¼ in. (32 mm) between the cable and the edge of the framing member. This is a Code requirement referenced in 300.4(D), to minimize the possibility of driving nails into the cable. All of 300.4 is devoted to the subject of protection against -- for more detailed discussion and illustrations relating to the physical protection of cables. ILL. 14 Methods of protecting cable installations in accessible attics. See 320.23 and 334.23. Cables run through bored holes in joists are considered protected if at least 1¼ (32 mm) or more from top or bottom. QUIZ: Note: Refer to the Code or plans where necessary. 1. List the switches, receptacles, and other wiring devices that are connected to Circuit B10. 2. a. Fill in the blank spaces. At least 120-volt receptacle must be installed in a bathroom within ______in. of the basin, and it must be on the wall _____ to the basin. The receptacle must not be installed ______ on the countertop. The receptacle must be protected. b. Circle the correct answers. A separate (15) (20)-ampere branch circuit must supply the receptacle(s) in bathrooms and (shall) (shall not) serve other loads. If a separate 20-ampere branch circuit serves a single bathroom, then that circuit (is permitted) /(is not permitted) to supply other loads in that bathroom. 3. What special type of switch is controlling the attic lights? 4. When installing cables in an accessible attic along the top of the floor joists ___ must be installed to protect the cables. 5. The total estimated volt-amperes for Circuit B10 has been calculated to be 1300 volt-amperes. How many amperes is this at 120 volts? ______ 6. If an attic is accessible through a scuttle hole, guard strips are installed to protect cables run across the top of the joists only within (6 ft [1.8m]) (12 ft [3.7m]) of the scuttle hole. Circle the correct answer. 7. What section(s) of the Code refers (refer) to the receptacle required for the laundry equipment? State briefly the requirements. 8. What is the current draw of the exhaust fan in the Laundry? 9. The following is a layout of the lighting circuit for the Laundry, Powder Room, Rear Entry Hall, and Attic. Complete the wiring diagram using colored pens or pencils to indicate conductor insulation color. The GFCI receptacle in the Powder Room isn't shown in the diagram because it's connected to a separate circuit, B21. 10. Laundry receptacle outlets are included in the residential load calculations at a value of volt-amperes per circuit. Choose one: 1000, 1500, 2000 volt-amperes. 11. List the various methods of connecting an electric clothes dryer. 12. a. What is the minimum power demand allowed by the Code for an electric dryer if no actual rating is available for the purpose of calculating feeder and service entrance conductor sizing? b. What is the current draw? 13. What is the maximum permitted current rating of a portable appliance on a 30-ampere branch circuit? 14. What provides motor running overcurrent protection for the dryer? 15. a. Must the metal frame of an electric clothes dryer be grounded? b. May the metal frame of an electric clothes dryer be grounded to the neutral conductor? 16. An electric dryer is rated at 7.5 kW and 120/240 volts, 3-wire, single-phase. The terminals on the dryer and panelboard are marked 75°C. a. What is the wattage rating? b. What is the current rating? c. What minimum size type THHN copper conductors are required? d. If EMT is used, what minimum size is required? 17. When a metal junction box is installed as part of the cable wiring to a clothes dryer or electric range, may this box be grounded to the circuit neutral conductor? 18. A residential air-conditioning unit is installed in the attic. a. Is a lighting outlet required? ______ b. What Code section applies? _______ c. If a lighting outlet is required, how shall it be controlled? ____ d. What Code section applies? ___ e. Is a receptacle outlet required? ______ f. What Code section applies? _____ 19. The Code states that a means must be provided to disconnect an appliance. In the case of an electric clothes dryer, the disconnecting means can be a. a separate disconnect switch located within sight of the appliance. b. a separate disconnect switch located out of sight from the appliance. The switch is capable of being locked in the "OFF" position. c. a cord-and-plug-connected arrangement. d. a circuit breaker in a panel that's within sight of the dryer or capable of being locked in the "Off" position. Choose the correct statement(s). Next: Top of Page | All Related Articles | Also See | Home |
