Article 440 Air-Conditioning and Refrigeration Equipment

Transcription

1 Mike Holt s Illustrated Guide to Understanding the NEC Requirements for Article 440 Air-Conditioning and Refrigeration Equipment Extracted from Mike Holt s Illustrated Guide to Understanding the National Electrical Code, Volume Edition Mike Holt Enterprises, Inc. 888.NEC.CODE ( ) Info@MikeHolt.com

2 ARTICLE 440 Air-Conditioning and Refrigeration Equipment IntroDUctIon to article 440 air-conditioning and refrigeration equipment This article applies to electrically driven air-conditioning and refrigeration equipment. The rules in this article add to, or amend, the rules in Article 430 and other articles. Each equipment manufacturer has the motors for a given air-conditioning unit built to its own specifi cations. Cooling and other characteristics are different from those of nonhermetic motors. For each motor, the manufacturer has worked out all of the details and supplied the correct protection, conductor sizing, and other information on the nameplate. The application itself with the compressor motor often on the other side of an exterior building wall from the normal power sources so it can exchange heat with free air poses additional problems, which the NEC addresses in Article 440. Part I. general scope. Article 440 applies to electrically driven airconditioning and refrigeration equipment Definitions. Hermetic Refrigerant Motor-Compressor. A compressor and motor enclosed in the same housing, operating in the refrigerant. rated-load current. The current resulting when the motor-compressor operates at rated load and rated voltage other articles. (B) Equipment with No Hermetic Motor-Compressors. Airconditioning and refrigeration equipment that do not have hermetic refrigerant motor-compressors, such as furnaces with evaporator coils, must comply with Article 422 for appliances, Article 424 for electric space-heating, and Article 430 for motors. (C) Household Refrigerant Motor-Compressor Appliances. Household refrigerators and freezers, drinking water coolers, and beverage dispensing machines are listed as appliances, and their installation must also comply with Article 422 for appliances. Figure Figure ampacity and rating. (A) Hermetic Refrigerant Motor-Compressor. For a her metic refrigerant motor-compressor, the rated-load current marked on the nameplate of the equipment is to be used in determining the rating of the disconnecting means, the branch-circuit conductors, the controller, and the branch-circuit short-circuit and ground-fault protection. Mike Holt Enterprises, Inc NEC.CODE ( ) 1

3 440.6 Air-Conditioning and Refrigeration Equipment Exception No. 1: The branch-circuit selection current must be used instead of the rated-load current if provided on the equipment nameplate. Part II. Disconnecting Means Author s Comment: Within Sight is visible and not more than 50 ft from each other [Article 100]. The disconnecting means can be mounted on or within the air-conditioning equipment, but it must not be located on panels designed to allow access to the equipment, or where it will obscure the equipment name plate. Figure Location. The disconnecting means for air-conditioning or refrigeration equipment must be located within sight from and readily accessible from the equipment. Figures and Figure Figure Exception No. 1: A disconnecting means isn t required to be within sight from the equipment, if the disconnecting means is capable of being individually locked in the open position, and if the equipment is essential to an industrial process in a facility that has written safety procedures, and where the conditions of maintenance and supervision ensure only qualified persons service the equipment. The provision for locking or adding a lock to the disconnecting means must be on the switch or circuit breaker, and it must remain in place with or without the lock installed. Exception No. 2: An accessible attachment plug and receptacle can serve as the disconnecting means. Author s Comment: The receptacle for the attachment plug isn t required to be readily accessible. Figure Mike Holt s Illustrated Guide to Understanding the National Electrical Code, Volume 1

4 Part III. overcurrent ProtectIon general. The branch-circuit conductors, control apparatus, and circuits supplying hermetic refrigerant motorcompressors must be protected against short circuits and ground faults in accordance with Author s Comment: If the equipment nameplate specifies Maximum Fuse Size, then a one-time or dual-element fuse must be used. Air-Conditioning and Refrigeration Equipment short-circuit and ground-fault overcurrent Device size. (A) Single Motor-Compressors. The short-circuit and groundfault protective device must not be more than 175 percent of the motor-compressor current rating. If the protective device sized at 175 percent isn t capable of carrying the starting current of the motor-compressor, the next size larger protective 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 are required for a 24A motor-compressor connected to a 240V circuit? Figure (a) 10 AWG, 40A (c) a or b Answer: (a) 10 AWG, 40A (b) 10 AWG, 60A (d) 10 AWG, 90A Step 1: Determine the branch-circuit conductor [Table and ]: 24A x 1.25 = 30A, 10 AWG, rated 30A at 75 C [Table ] Step 2: Determine the branch-circuit protection [240.6(A) and (A)]: 24A x 1.75 = 42A, next size down = 40A If the 40A short-circuit and ground-fault protective device isn t capable of carrying the starting current, then the protective device can be sized up to 225 percent of the equipment load current rating. 24A x 2.25 = 54A, next size down 50A (B) Several Motor-Compressors. Where the equipment incorporates more than one hermetic refrigerant motor-compressor, or a hermetic refrigerant motor-compressor and other motors or other loads, the equipment short-circuit and ground-fault protection must be sized as follows: Figure (1) Motor-Compressor Largest Load. The rating of the branch-circuit short-circuit and ground-fault protective device must not be more than the largest motor-compressor short-circuit ground-fault overcurrent 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]. Part IV. conductor sizing conductor size for single Motor-compressors. 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 Comment: Branch-circuit conductors for a single motor-compressor must have short-circuit and ground-fault protection sized between 175 percent and 225 percent of the rated-load current [440.22(A)]. Mike Holt Enterprises, Inc NEC.CODE ( ) 3

5 Air-Conditioning and Refrigeration Equipment Question: What size conductor and overcurrent device are required for an 18A motor compressor? Figure (a) 12 AWG, 30A (c) a or b Answer: (a) 12 AWG, 30A (b) 10 AWG, 50A (d) 10 AWG, 60A Step 1: Determine the branch-circuit conductor [Table and ]: 18A x 1.25 = 22.50A, 12 AWG, rated 25A at 75 C [Table ] Step 2: Determine the branch-circuit protection [240.6(A) and (A)]: 18A x 1.75 = 31.50A, next size down = 30A If the 30A short-circuit and ground-fault protection device isn t capable of carrying the starting current, then the protective device can be sized up to 225 percent of the equipment load current rating. 18A x 2.25 = 40.50A, next size down 40A conductor size for several Motor-compressors. Conductors that supply several motor-compressors must have an ampacity not less than 125 percent of the highest motor-compressor current of the group, plus the sum of the rated load or branch-circuit selection current ratings of the other compressors. Author s Comment: These conductors must be protected against short circuits and ground faults in accordance with (B)(1). Part VII. room air conditioners The requirements in this Part apply to a cord-and-plug-connected room air conditioner of the window or in-wall type that incorporates a hermetic refrigerant motor-compressor rated not over 40A, 250V, single-phase [440.60] Branch-circuit requirements. (A) Sizing Conductors and Protection. Branch-circuit conductors for a cord-and-plug-connected room air conditioner must have an ampacity not less than 125 percent of the ratedload currents [440.32]. (B) Separate Circuit. Where the room air conditioner is the only load on a circuit, the marked rating of the air conditioner must not exceed 80 percent of the rating of the circuit overcurrent device [210.3]. (C) Other Loads on Circuit. The total rating of a cord-andplug-connected room air conditioner must not exceed 50 percent of the rating of a branch circuit where lighting outlets, other appliances, or general-use receptacles are also supplied. Figure Disconnecting Means. An attachment plug and receptacle can serve as the disconnecting means for a room air conditioner, provided: Figure Figure Author s Comment: A 30A or 40A overcurrent device is permitted to protect a 12 AWG conductor for an air-conditioning circuit. See 240.4(G) for details. (1) The manual controls on the room air conditioner are readily accessible and within 6 ft of the floor, or (2) A readily accessible disconnecting means is within sight from the room air conditioner. Author s Comment: Within Sight is visible and not more than 50 ft from each other [Article 100]. 4 Mike Holt s Illustrated Guide to Understanding the National Electrical Code, Volume 1

6 Air-Conditioning and Refrigeration Equipment Supply Cords. Where a flexible cord is used to supply a room air conditioner, the cord must not exceed 10 ft for 120V units, or 6 ft for 208V or 240V units Leakage Current Detector-Interrupter and Arc-Fault Circuit Interrupter. Single-phase cord-andplug-connected room air conditioners must be provided with a factory-installed leakage current detector, or with an arcfault circuit-interrupter (AFCI). Figure Figure Mike Holt Enterprises, Inc NEC.CODE ( ) 5

7 Article 440 Practice Questions ARTICLE 440 Practice Questions article 440. air-conditioning and refrigerating equipment PractIce QUestIons 1. Article 440 applies to electric motor-driven air-conditioning and refrigerating equipment that has a hermetic refrigerant motor-compressor. (a) True (b) False 2. Equipment such as shall be considered appliances, and the provisions of Article 422 apply in addition to Article 440. (a) room air conditioners (b) household refrigerators and freezers (c) drinking water coolers and beverage dispensers (d) all of these 3. Where the air conditioner disconnecting means is not within sight from the equipment, the provision for locking or adding a lock to the disconnecting means shall be on the switch or circuit breaker and remain in place the lock installed. (a) with (b) without (c) with or without (d) none of these 4. Branch-circuit conductors supplying a single a/c motorcompressor shall have an ampacity not less than percent of either the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater. (a) 100 (b) 125 (c) 150 (d) An attachment plug and receptacle can serve as the disconnecting means for a single-phase room air conditioner rated 250 volts or less if. (a) the manual controls on the room air conditioner are readily accessible and located within 6 ft of the floor (b) an approved manually operable disconnecting means is installed in a readily accessible lo cation within sight from the room air conditioner (c) a or b (d) a and b Answers: 1. (a) (d) 440.3(C) 3. (c) Ex 1 4. (b) (c) Mike Holt s Illustrated Guide to Understanding the National Electrical Code, Volume 1