Article 100 of the National Electrical Code (NEC) defines “equipment” as a general term, including fittings, devices, appliances, luminaires, apparatus, machinery and the like, used as a part of, or in connection with, an electrical installation. An appliance, also defined in Article 100, is utilization equipment, generally other than industrial, normally built in standardized sizes or types and installed or connected as a unit to perform one or more functions, such as clothes washing, air conditioning, food mixing, deep frying, etc. “Equipment” is a general term that includes appliances, and the term “appliance” is utilization equipment. So what is “utilization equipment”? (Sometimes, when looking at a definition of a word or term, the definition may contain words or terms that also need defining).


Utilization equipment uses electric energy for electronic, electromechanical, chemical, heating, lighting or similar purposes. Sizing conductors for equipment involves referencing the usual tables that pertain to conductor sizing, such as 310.15(B)(16), 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c). It also involves referencing the usual sections, such as 110.14(C), 210.19(A), 210.23 and 240.4. When the equipment is an appliance, it will also be necessary to reference Article 422. In accordance with the scope of Article 422 (422.1), the article covers electrical appliances used in any occupancy.


Part II of Article 422 contains requirements for the appliance installation. It may be necessary to reference different sections and even different articles when sizing conductors. For example, an electric-storage-type water heater will be installed in a small commercial occupancy. This fixed-storage-type water heater will have a capacity of 55 gallons. The nameplate on the water heater shows 4,500 total watts (W) at 240 volts (V). The branch-circuit conductors supplying power to this water heater will be THHN copper, and the conductors will be installed in electrical metallic tubing (EMT) and flexible metal conduit (FMC). What is the minimum size conductor required to supply this water heater?


First, calculate this water heater’s current draw. Since watts and voltage are given, divide the nameplate watts by the nameplate volts to find the amperes (A). This water has a current draw of 18.75A (4,500 ÷ 240 = 18.75). The third paragraph in 422.10(A) specifies what to do if the appliance is a continuous load, but how do we know if the appliance will be a continuous load?


In accordance with the definition in Article 100, a continuous load is a load where the maximum current is expected to continue for three hours or more. Instead of trying to figure out if this water heater will be a maximum current for three hours or more, look at the provision in 422.13. A fixed-storage-type water heater that has a capacity of 120 gallons or less shall be considered a continuous load for the purposes of sizing branch circuits. Because of 422.13, this water heater shall be considered a continuous load. In accordance with the third paragraph in 422.10(A), the branch-circuit rating for an appliance that is a continuous load, other than a motor-operated appliance, shall not be less than 125 percent of the marked rating.


The last part of the sentence pertains to a branch-circuit device and its assembly that is listed for continuous loading at 100 percent of its rating. Since this example did not state that the circuit device and its assembly would be listed for continuous loading at 100 percent, multiply the current draw of the water heater by 125 percent. The conductor must have an allowable ampacity of at least 23A (18.75 × 125% = 23.4 = 23). In accordance with the 75°C column of Table 310.15(B)(16), a 12 AWG conductor is good for 25A. But a 12 AWG conductor is one of the conductors with a double asterisk, which references a footnote at the bottom of Table 310.15(B)(16), and the footnote refers to 240.4(D) for conductor overcurrent protection limitations. Unless 240.4(E) or (G) specifically permits, the overcurrent protection shall not exceed 20A for 12 AWG copper [240.4(D)(5)].


In accordance with 210.20 and 210.20(A), an overcurrent protective device that has a rating of at least 125 percent of the continuous load shall protect branch-circuit conductors and equipment. Because the branch circuit supplying this water heater is considered a continuous load, the rating of the overcurrent protective device shall not be less than 125 percent of the load. The load of this water heater multiplied by 125 percent is 23A (18.75 × 125% = 
23.4 = 23).


A list of standard ampere ratings for fuses and inverse-time circuit breakers is in 240.6(A), and 23 is not a standard rating. In accordance with 240.4(B), the next higher standard size is permitted. The minimum rating for the overcurrent device protecting this water heater is 25A. Since the rating of the overcurrent device must be at least 25A, a 12 AWG conductor would not be permitted because the maximum rating for a 12 AWG conductor supplying this load is 20A. Therefore, the minimum size conductor required to supply this water heater is 10 AWG (see Figure 1).


Some provisions in the NEC specify minimum sizes, such as minimum size conductor and minimum size overcurrent device. Other provisions specify maximum sizes, such as maximum number of conductors in a raceway and maximum size overcurrent device. Notice that overcurrent devices are examples of both minimum sizes and maximum sizes. Sometimes the minimum size overcurrent device is specified in the Code, sometimes the maximum size overcurrent device is specified, and sometimes both minimum and maximum sizes are specified. As previously mentioned, the minimum overcurrent device rating for the water heater in Figure 1 is 25A, but is there a maximum size overcurrent device and, if so, what is it?


For this appliance, there is a provision that specifies the maximum overcurrent device rating. If the branch circuit supplies a single non-motor-operated appliance, the rating of overcurrent protection shall comply with 422.11(E)(1) through (3). In accordance with 422.11(E)(3), the rating of overcurrent protection shall not exceed 150 percent of the appliance-rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3A. This section continues on by stating, where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted. The current draw, or load, of this water heater was previously calculated to be 18.75A. The load multiplied by 150 percent is 28A (18.75 × 150% = 28.125 = 28). Since 28 is not a standard overcurrent device ampere rating and the next higher standard rating is permitted, the maximum size fuse or breaker permitted for this branch circuit is 30A (see Figure 2).


Section 422.11 provides a provision if the single non-motor-operated appliance is rated over 13.3A, but it also provides a provision if the single non-motor-­operated appliance is rated 13.3A or less. In accordance with 422.11(E)(2), the rating of overcurrent protection shall not exceed 20A if the overcurrent protection rating is not marked and the appliance is rated 13.3A or less. For example, a 28-­gallon electric-storage-type water heater will be installed in a small commercial occupancy. The nameplate shows 3,000 total watts at 240V. The overcurrent protection rating is not marked on this water heater. The branch-circuit conductors supplying power to this water heater will be THHN copper, and the conductors will be installed in electrical metallic tubing (EMT) and flexible metal conduit (FMC). What is the minimum size conductor required to supply this water heater, and what is the maximum size or rating for the overcurrent protective device?


This water heater has a current draw of 12.5A (3,000 ÷ 240 = 12.5). The conductor must have an allowable ampacity of at least 16A (12.5 × 125% = 15.625 = 16). In accordance with the 75°C column of Table 310.15(B)(16), a 14 AWG conductor is good for 20A. But, as stated in 240.4(D)(3), the overcurrent shall not exceed 15A for a 14 AWG copper conductor. Since the rating for the overcurrent device protecting this branch circuit shall be at least 16 amperes and the overcurrent shall not exceed 15 amps for a 14 AWG conductor, the minimum size conductor required to supply this water heater is 12 AWG.


As stated in 422.11(E)(2), the rating of overcurrent protection shall not exceed 20A if the overcurrent protection rating is not marked and the appliance is rated 13.3A or less. Since the overcurrent protection rating is not marked and the water heater draws only 12.5A, the maximum rating for the overcurrent protective device is 20A (see Figure 3).


Next month’s column continues the discussion of sizing conductors.