The NEC does not restrict the methods used for wiring heavy appliances. Use conduit or cable as you choose.
If the appliance is to be connected by cord and plug, run your cable up to the receptacle, which may be either flush-mounted or surface-mounted. The NEC demands that the receptacle be located within 6 feet of the intended location of the appliance; with good planning it should be possible to locate it even closer thus simplifying installation of the appliance.
White wire re-identified for use as black wire White wire may be used only for the grounded wire. But that wire does not run to any appliance operating at 240 volts. Therefore the wires running to a 240-volt load may be any color except white or green. When you use a two-wire cable to connect a 240-volt load, the cable contains one black wire and one white wire, but the white wire must not be used. What can be done? Follow NEC 200.7(C) instructions to re-identify the wire.
Provision for grounding of appliances on existing circuits NEC 250.140 makes an important provision that applies only to existing circuits. While many appliances must be grounded, in the case of ranges (including counter units and separate ovens) and dryers, their frames may be grounded to the neutral circuit conductor, provided it’s 10 AWG or heavier. See NEC 250.140. Moreover, for these appliances and no others, you may use service entrance cable with a bare neutral, provided it runs from the appliance directly to the service equipment.
Ranges and dryers are 120/240-volt appliances, and the neutral wire carries current in normal operation. Three-wire service-entrance cable with a bare neutral may be used in wiring 240-volt appliances such as water heaters, etc. to which the neutral does not run, provided the bare wire of the cable is used only as a grounding wire.
Ranges In some ranges, and in all older ranges, a surface burner operates at either 120 or 240 volts, depending on whether it’s turned to low, medium, or high heat. The individual burners are connected within the range in a manner that makes it impossible for the neutral wire to carry as many amperes as the two hot wires. For that reason, the wires to the range usually include a neutral that is one size smaller than the hot wires. For most ranges, two 6 AWG plus an 8 AWG neutral are used; for smaller ranges, two 8 AWG with a 10 AWG neutral are occasionally used. Surface burners on most modern ranges operate at 240 volts and have stepless control. The neutral is still needed for operating the clock, timer, oven light, etc.
Run your circuit up to the range receptacle of this figure; this is rated at 50 amps, 125/250 volts. The range is connected to the receptacle using a pigtail cord shown in the same illustration. This also serves as the disconnecting means.
Grounding the range The NEC requires that the frame of the range be grounded by means of a separate green (or bare) grounding wire, using a four-wire cord and plug (unless it’s permanently connected). On existing circuits the range is permitted to be grounded through the neutral wire, in which case a bonding strap is connected between the neutral wire and the frame of the range, and the cord and plug are three-wire. The requirement to use four-wire supplies for ranges took effect with the 1996 NEC. Check that the bonding strap is not connected in new installations where a four-wire cord is used.
Receptacle outlet for gas range Install a receptacle outlet for a gas range. This receptacle, which can be on the small appliance circuit, is for the supply of a gas ignition system, lights, clock, and timer.
Sectional ranges The trend is away from complete self-contained ranges, consisting of oven plus burners, toward individual units. The oven is a separate unit, installed in or on the wall. Groups of burners in a single section are installed in or on the kitchen counter where convenient. This makes for a very flexible arrangement and permits you to use imagination in laying out a custom-designed kitchen. The NEC calls such separate ovens “wall mounted ovens’ and the burners “counter mounted cooking units’ Here they will be referred to merely as ovens and cooking units or counter units.
Unlike self-contained ranges, ovens and cooking units are considered fastened in place. They may all be either permanently connected or cord-and-plug connected. Two basic methods are used in the wiring of ovens and cooking units. Supplying a separate circuit for the oven and another for the cooking unit is one method. The alternate method is to install one 50-amp circuit for the oven and cooking unit combined. Any type of wiring method may be used. Regardless of the wiring method used, the frame of the oven or cooking unit must be grounded. Where a separate circuit is installed for the oven, use wire with the ampacity required by the load. The oven will probably be rated about 4,500 watts, which at 240 volts is equivalent to about 19 amps, 50 12 AWG wire would be suitable. At the oven, the circuit wires may run directly to the oven, but some prefer to install a pigtail cord and a receptacle. Note that because the plug and receptacle are concealed behind an appliance that is fastened in place, the plug won’t serve as the disconnecting means as it does when installing a self-contained range.
To wire the cooking units, proceed exactly as for the oven, using no smaller than 10 AWG wire. This size wire has an ampacity (current rating) of 30 amps and will provide a maximum of 7,200 watts, which will take care of most cooking units. Use a pigtail cord and a receptacle if you wish to make it easy to service the unit.
If you install a single circuit for oven and cooking units combined, it must be a three- wire, 50-amp circuit. Any wiring method maybe used, including service-entrance cable with a bare equipment grounding conductor. The receptacles must be the 50- amp type, and may be flush receptacles installed in outlet boxes, or the surface type shown here. The circuit will be as below. The wires to the receptacles must be the same size as the circuit wires. But the wires from the receptacles to the oven or cooking unit may be smaller, per NEC 210.19(A) (3) Exception l,provided they are heavy enough for the load, not smaller than 12 AWG (10 AWG if used for grounding), and not longer than necessary to service the appliance. The receptacles are not required but they may be convenient for installation. The oven or cooking unit may be connected directly to the circuit wires in the junction boxes. The NEC exception permits smaller wires between the junction box and the appliance under the same conditions specified for when receptacles are used.
Diag. above: It’s common to provide separate circuits for oven and counter units, but both may be placed on one circuit as shown.
Clothes dryers: An electric dryer is a 120/240-volt appliance. Wire as for a range.
The NEC requires a three-pole, four-wire, grounding-type, 30-amp receptacle (see K), and a four-wire pigtail cord similar to that used for a range but with smaller wires. The plug and receptacle serve as the disconnecting means.
Grounding the dryer: For existing circuits only, NEC 250.140 permits the frame of the dryer to be grounded to the neutral of the three wires if it’s not smaller than 10 AWG. Service-entrance cable with a bare neutral is permitted where it runs from the service location directly to the dryer receptacle. For these existing applications only, a three-wire receptacle may be used (configuration I).
Clothes washers: Washers are equipped with a cord and plug for easier servicing, so provide a 20-amp grounding receptacle on a 20-amp circuit. No separate switch is required.
Water heaters: NEC 210. 19(A)( 1) requires that loads expected to be on continuously for three hours or more must not exceed 80 percent of the branch circuit rating. Dwellings and farms seldom have such continuous loads, but a domestic water heater is required to be considered in this category by NEC 422.13. This means that a 4,500-watt water heater must be on a 25-amp circuit, not a 20-amp. (Dividing 4,500 watts by 240 volts equals 18.7 amps, but 18.7 is 93.5% of 20. The next higher standard overcurrent device rating is 25 amps, and 18.7 is 75% of 25.) This additional 25 percent of the continuous loads must be added to feeder and service calculations also, per NEC 215.2(A)(1) and 230.42(A)(1).
Look at the water heater terminal box for a marked temperature rating for the branch circuit wires. If there is no marking, the circuit wiring can be TW (or other 60°C wire), but if marked 7 5°C, then use a wire with an H in its designation (or HH if marked 90°C). For further information, see NEC Article 310. Where higher temperature wires are required, it’s common to splice the ordinary branch circuit wires in a junction box near the water heater to short lengths of the higher temperature wire extending to the heater.
In some localities, power for heating water is sold at a reduced rate, with the heater connected to the circuit through a special electrically operated switch furnished by the power supplier. The switch connects the heater to the power line only during off-peak hours. Each day for several periods of several hours each, water cannot be heated. If your installation is of this type, do the wiring as already described, except that the wires should start from the power supplier’s time switch instead of from your service equipment.
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