Reviewing and understanding the information on equipment nameplates is important in properly evaluating an air-conditioner or heat pump installation. It also simplifies the selection of the correct branch-circuit wire, overcurrent protection and disconnect sizes. Most all the information needed by the installer can be found by reference to the units data name-plate. The following is an example of the type of information found on the nameplate for a residential central air-conditioning unit.
|Model No. RAKA-036JAZ MFD. 03/94Serial No. 5340 F0994 8995 Outdoor Use |
Volts 208/230 Phase 1 Hertz 60
Compressor R.L.A. 18.0/18.0 L.R.A. 96
Outdoor Fan Motor F.L.A. 1.3 HP. 1/5
Min. supply circuit ampacity 24/24 amp
Max. fuse or ckt. brk. size* 40/40 amp
Min. fuse or ckt. brk. size* 30/30 amp
Design pressure high 300 PSIG
Design pressure low 150 PSIG
Outdoor Units Factory Charge 77 OZ. R22
Total System Charge OZ. R22
See instructions inside access panel
*HACR type breaker for U.S.A.
Air-conditioning and heat pump equipment have a hermetic motor-compressor and are not treated the same as a conventional electric motor. The hermetic motor-compressor operates in the refrigerant environment and does not have a horsepower or full-load current rating such as a standard motor. Special terms are used to provide the necessary information to properly install wiring for this equipment.
One of the terms noted on the above nameplate is "Compressor R.L.A.” This is the Rated-Load Amperes or Rated-Load Current for the motor-compressor and is established by the manufacturer of the equipment. The rated-load current is the current resulting when the motor-compressor is operated at the rated load, rated voltage and rated frequency of the equipment it serves. This value is used in calculating the minimum circuit ampacity and overcurrent protective device ratings specified on the nameplate for this equipment. The RLA for our example is 18.0 amperes.
Another term noted on the air-conditioner nameplate is "Compressor L.R.A.” This term represents Locked-Rotor Amperes and is the maximum current flowing to the motor when it is in a locked, or not turning, condition. This value is necessary to ensure that the air-conditioner disconnecting means and controller have proper interrupting capacities. The LRA for our example is 96 amperes.
The term "Min. supply circuit ampacity,” or similar wording, is the minimum circuit ampacity required to select conductor size and switch rating for the unit. This value is determined by the following formula:
Minimum Circuit Ampacity = (RLA x 1.25) + Other Loads
The term "Max fuse or ckt brk size” indicates the maximum fuse or circuit breaker size permitted. The manufacturer has selected a rating that will permit the motor to start as well as provide overcurrent protection. The term "Min fuse or ckt brk fuse” rating indicates the smallest rating that will allow the motor to start.
The Rated Load Amperes (RLA) is used in calculating the maximum overcurrent protection permitted for the unit. Later in this chapter we will include a calculation for the unit covered by the above nameplate.
In some cases, the equipment is also marked with a "Branch-Circuit Selection Current” (BCSC). This is a value in amperes that must be used instead of the rated-load current for determining ratings of motor branch-circuit conductors, disconnecting means, controllers, and branch-circuit short-circuit and ground-fault protective devices whenever the running overload protective device permits a sustained current greater than the rated-load current. The value of branch-circuit selection current will always be equal to or greater than the marked rated-load current. Since the air-conditioning nameplate included in this chapter does not include a branch-circuit selection current, the rated-load current, or in this case RLA, is used for the calculations. SeeNECSections 440-2 and 440-4.
Note that the nameplate also references "HACR type breaker.” The marking "HACR” means Heating, Air Conditioning and Refrigeration. This marking means the circuit breaker has been tested and found suitable for use on this equipment including providing adequate protection for the smaller motor of the group, which is the outdoor fan. Circuit breakers used to supply this unit must be marked "HACR.”
Most circuit breakers manufactured today are HACR rated. This marking is common on most circuit breakers manufactured today but may not be present on older breakers located in existing equipment.
Remember thatNECSection 110-3(b) requires compliance with nameplate markings. If the nameplate specifies fuses only, substitution of even a HACR rated breaker marked only for fuses or if the breakers must be of the HACR type, failure to comply with the marking is a violation of this section. Generally the manufacturer offers a choice of either fuses or HACR rated circuit breakers. Check the nameplate information to make sure.
The required ampacity of branch-circuit conductors and rating of equipment for a hermetic refrigerant motor-compressor are based upon marking found on the unit nameplate giving the rated-load current. This information is necessary to determine the rating or ampacity of the disconnecting means, the branch-circuit conductors, the controller, the branch-circuit short-circuit and ground-fault protection, and the separate motor overload protection. SeeNECSection 440-6(b).
Branch-Circuit Conductor Size
For a typical air-conditioning unit or heat pump outdoor unit which has a motor-compressor and additional load(s), such as a fan motor, the conductors supplying this equipment must have an ampacity not less than 125 percent of either the rated-load or branch-circuit selection current, whichever is larger, plus the full-load current of the fan motor. For the example nameplate, this value is:
(RLA x 1.25) + Fan Motor FLA
18.0 x 1.25 + 1.3 = 23.8 amperes
This value rounded up to 24 is the "MIN SUPPLY CIRCUIT AMPACITY” stated on the nameplate and is the required minimum ampacity of the branch-circuit conductors selected fromNECTable 310-16. Since the equipment nameplate includes this value, it is not necessary for the installer or inspector to perform this calculation.
NEC Table 310-16 shows that a No. 12 Type TW, THW or THWN copper conductor can safely carry 25 amperes continuously where operated in an ambient temperature not exceeding 86°F. Where the temperature in an attic or on the roof reaches temperatures in excess of this figure, ampacity correction factors listed inNECTable 310-16 must be applied, which will make it necessary to increase the size of the conductors to compensate for the rise in temperature.
NEC Section 240-3(d) requires that the "overcurrent protection” must not exceed 20 amperes for a No. 12 conductor unless otherwise specifically permitted in Sections 240-3(e) through (g). Section 240-3(g) permits air conditioning circuit conductors to be protected in accord with Parts C and F of Article 440. Section 440-21 specifically states that the provisions of Part C are "in addition to or amendatory of the provisions of Article 240.” For example, the air conditioner nameplate marking indicates a "Maximum Fuse or Circuit Breaker Size” of 40 amperes. The minimum supply circuit ampacity is 24-amperes. In this case the nameplate on the air conditioner is marked for a Maximum Fuse or Circuit Breaker Size of 40 amperes, which will satisfy the requirements. Consequently, if no derating for ambient temperature is required, No. 12 conductors having an ampacity of 25 amperes are acceptable to supply this unit.
The concept for protection where a No. 12 copper wire with an ampacity of 25 amperes is permitted to have overcurrent protection of 40 amperes is as follows:
1. The 40-ampere fuse or circuit breaker at the origination of the circuit will protect the conductors from short circuit [ungrounded (hot) conductors which fault together, line-to-line] and ground fault [ungrounded (hot) conductor(s) which fault to the equipment grounding conductor or grounded equipment].
2. The conductor is protected from overload by the running overcurrent device usually contained in the motor controller.
The combination of the two protection elements provides the overcurrent protection for safety.
Branch-Circuit Maximum Overcurrent Protection Rating
Paragraph 36.15 of the UL Standard 1995Heating and Cooling Equipment requires the maximum current rating of the branch-circuit overcurrent protection be based on:
(RLA x 2.25) + Other Loads (Fan Motor FLA)
18.0 x 2.25 + 1.3 = 41.8 amperes
If this calculated value is not a standard current rating of an overcurrent protective device, paragraph 36.16 of UL 1995 requires use of the next lower standard rating. In this example, the next lower standard device is 40 amperes as stated on the nameplate. Note here again it is not necessary to actually perform this calculation. It has been done, and the information is included on the units nameplate.
If the nameplate includes a "MINIMUM FUSE OR CIRCUIT BREAKER SIZE,” thenNECSection 110-3(b) would also require compliance with that marking in addition to the marking of the "MAXIMUM FUSE OR CIRCUIT BREAKER SIZE.”
Disconnecting Means Rating
Where the air-conditioning or heat pump compressor unit consists of a hermetic refrigerant motor-compressor(s) in combination with other loads, such as the fan motor, the horsepower rating of the disconnecting means is based on the summation of all currents at rated-load condition and also at locked-rotor condition.
In the example used in this chapter, the 18.0 ampere.0-ampere RLA of the compressor motor is added to the 1.3 ampere FLA of the fan motor. The total of 19.3 amperes is then considered to be the equivalent full-load current for the combined load. According toNECTable 430-148, the full-load current rating of a 230-volt, single-phase, 3 horsepower motor is 17 amperes, while the full-load current rating of a 230-volt, single-phase, 5-horsepower motor is 28 amperes. Consequently, since the equivalent full-load current of the example A/C unit is 19.3 amperes, we must use the next higher rating, and the disconnect switch must have a minimum of a 5-horsepower, 230-volt, single-phase rating.
The ampere rating of the disconnecting means must also be a least 115 percent of the sum of all currents at rated-load condition. This minimum rating would then be 115 percent x
19.3 amperes = 22.3 amperes. If the disconnecting means includes or serves as the branch-circuit overcurrent protection for the unit, the rating required for the overcurrent device, rather than this minimum rating, would generally be the determining factor in sizing the disconnecting means. A fused disconnect switch containing either the maximum or minimum sizes of fuses listed on the nameplate would exceed this 115 percent minimum requirement. If an unfused disconnect switch is used as the disconnecting means, however, then this 115 percent rating and the horsepower rating would establish the minimum switch rating.
There is one other consideration in establishing the correct size of the disconnecting means serving the air- conditioning unit. The disconnecting means rating must also be based on currents at locked-rotor condition. Refer to NEC Table 430151A for the conversion of locked-rotor current to horsepower. In our example, the nameplate indicates that the motor-compressor LRA is 96 amperes. Since the nameplate does not give a LRA for the fan motor, we assume it to be six times the FLA or 6 x 1.3 amperes = 7.8 amperes. Adding this to the motor-compressor LRA of 96 amperes gives us an equivalent LRA for the combined load of 103.8 amperes. Again referring toNECTable 430-151, we find that for a single-phase, 230-volt motor with a 103.8 amperes motor locked-rotor current, the disconnect switch should be based on a 5-horsepower rating. SeeNECSection 440-12.
Disconnecting Means Location
NEC Section 440-14 covers the required location of a disconnecting means for an air-conditioner or heat pump compressor. This rule specifically points out that the disconnecting means is required to be located within sight from and readily accessible from the air-conditioning equipment. The following twoNECArticle 100 definitions must be clearly understood.
"In Sight From (Within Sight From, Within Sight)”: Where thisCodespecifies that one equipment shall be "in sight from,” "within sight from,” or "within sight,” etc., of another equipment, the specified equipment is to be visible and not more than 50 ft. distant from the other.”N
"Accessible, Readily: (Readily accessible.)”: Capable of being reached quickly for operation, renewal, or inspections, without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, chairs, etc.”N
This disconnecting means is permitted to be installed on or within the air-conditioning equipment. An air-conditioner or heat pump compressor is generally located on a concrete pad located at the outside of a one- or two-family dwelling. It may also be located under the house in a crawl space or on the roof. It is important to remember that the definitions ofwithin sight and readily accessible have a significant meaning in this application.
The disconnecting means is usually located next to the air-conditioning unit and is, therefore, considered as being readily accessible since the proper working space should be provided in accordance with NEC Section 110-26.
However, where the disconnecting means is located "behind or above” the air conditioning unit, accessibility to the disconnect will be hindered and will be in violation of the working space requirements of NEC Section 110-26(a). This type of installation is incorrect and still remains as a very common problem in the field.
The purpose of the required disconnecting means is to provide a "ready and visible means” of disconnect for the person who will service or repair the equipment. The requirements of NEC Article 430, where a "locking type” of disconnecting means may be permitted out-of-sight of the motor, are not applicable for this equipment.
Note: A disconnecting means as described above is not required for cord- and plug-connected equipment such as room air conditioners.
Working space about electrical equipment that is likely to "require examination, adjustment, servicing, or maintenance while energized”Nmust be provided in accordance with Table 110-26(a). The working clearance must be in the direction of access to the equipment, or the part of the equipment, that is likely to be worked on while there are live exposed parts. It is very common for service persons to examine or test this equipment while it is energized.
Generally, this working space is 30 inches wide and 36 inches deep. Compliance with this working space rule requires that consideration be given to providing safe access at the time the equipment is being installed. Clear working space is required in front of access panels on this equipment.
The closest a/c unit appears to be in compliance with the workable space requirements of Section 110-26 while the further a/c unit disconnects are clearly in violation of that section
Indoor Heat Pump Equipment
An indoor air-handling unit is installed for typical heat pump split systems. Refrigerant lines are run from the outdoor unit to the indoor unit that may be located in the crawl space, attic or indoors, such as in a utility closet or room. The indoor unit includes a fan for circulating air through the dwelling and controls, as well as the refrigeration coil. Where desired, resistance heating elements are added to the indoor unit to serve as backup heat in case of compressor failure and to provide extra heating capacity to provide faster heating recovery.
Many of the same rules apply to indoor units as apply to electric furnaces. A disconnecting means rated for the load to be served is required within sight of the indoor unit. In some cases, this disconnecting means consists of one or more circuit breakers that are located in the unit and are operational from outside the unit.
The minimum size of the branch circuit to the indoor unit is required to be not less that 125 percent of the resistance heat and motor load. SeeNECSection 424-3(b).
Room Air Conditioners
A room air conditioner is considered to be an alternating-current appliance of the air-cooled window, console or in-wall type that is installed in the conditioned room and incorporates a hermetic motor-compressor. The following requirements cover equipment rated not over 250 volts, single phase, and such equipment may be cord- and plug-connected.
In determining branch-circuit requirements for a room air conditioner, a cord- and attachment plug-connected unit is considered as a single motor unit if its rating is not more than 40 amperes, 250 volts, single phase; total rated-load current is shown on the air-conditioner nameplate; and the rating of the branch-circuit protective device does not exceed the ampacity of the branch-circuit conductors or rating of the receptacle, whichever is less.
The total marked rating of a cord- and attachment plug-connected room air conditioner shall not exceed 80 percent of the branch-circuit rating where no other loads are supplied. If the branch circuit supplies lighting units or other appliances, the rating of the unit cannot exceed 50 percent of the rating of the branch circuit. SeeNECSection 440-62.
An attachment plug and properly rated receptacle is permitted to serve as the required disconnecting means for a single-phase room air conditioner rated 250 volts or less if the following conditions are met:
1. The manual controls on the room air conditioner are readily accessible and located within 6 feet from the floor, or
2. An approved manually operable switch is installed in a readily accessible location that is within sight from the room air conditioner. SeeNECSection 440-63.
Where a flexible cord is used to supply a room air conditioner, the length of such cord cannot exceed:
1. 10 feet for a nominal, 120-volt rating, or 2. 6 feet for a nominal 208- or 240-volt rating. SeeNECSection 440-64.
A room air conditioner that is fastened in place or connected by permanent wiring methods (fixed) requires that any exposed noncurrent-carrying metal parts likely to become energized are to be properly grounded under any of the following conditions:
1. Where an air conditioner is located within 8 feet vertically or 5 feet horizontally of ground or grounded metal objects and subject to contact by persons.
2. Where located in a wet or damp location and not isolated.
3. Where in electrical contact with metal.
4. Where supplied by a metal-clad, metal-sheathed, metal-raceway, or other wiring method that provides an equipment ground. See NEC Sections 250-110, 250-112, and 250-114.
See also NEC Article 440, Part G.
Safety Standard Information for Overcurrent Protection Requirements for Air-Conditioning Equipment
Section 110-3(b) of theNational Electrical Codestates: "Installation and Use. Listed or labeled equipment shall be installed, used, or both, in accordance with any instructions included in the listing or labeling.”N
Qualified laboratories typically list air-conditioning and heating equipment in accord with the following standards: This listing or labeling is performed by qualified electrical testing laboratories in accordance with the following UL Standards.
UL1995 —Heating and Cooling Equipment (This standard covers central heating, central air-conditioning, and heat pumps.) (UL1995 applies to central air-conditioning units and heat pumps.)
UL484 –Room Air Conditioners
These product safety standards detail the necessary safety tests and determine the required nameplate markings and instructions that are included by the manufacturer of the equipment. For example, paragraph 36.3(i) of UL 1995 specifies the equipment shall be marked with a "maximum overcurrent protective device size.” A typical nameplate will show the "MAXIMUM FUSE” and/or "MAXIMUM CIRCUIT BREAKER” size. If the nameplate specifies only fuses, then the unit is intended to be protected by fuses only. If the nameplate requires HACR (Heating, Air Conditioning and Refrigeration) circuit breakers, then the circuit breaker protecting the unit must be marked "HACR.”
If the nameplate includes both fuses and HACR circuit breakers, as is the case of our nameplate example in this chapter, then either is acceptable.
As noted above,NECSection 110-3(b) would require that the branch-circuit overcurrent protective device comply with the type and size specified on the air- conditioner nameplate.
For room air conditioners, the nameplate will also be marked to show the type and maximum size overcurrent protection permitted for the unit. The comments previously discussed relative to use of fuses or HACR circuit breakers are applicable to room or window units as well as to central air conditioners and heat pumps. Where a room air conditioner is added to an existing dwelling and supplied from an existing panelboard or load center, it is important to verify the branch-circuit overcurrent device for the circuit supplying the air conditioner complies with the type and size overcurrent protection stated on the units nameplate.
Product Safety Standard Requirements
It is recommended that the following electrical product safety guide card information and product safety standards be consulted for additional guidance on the proper installation, operation and use of electrical equipment covered in this chapter. The four letter code in parenthesis refers to the product category in the Underwriters Laboratories Directories.
- Equipment for Use in Ordinary Locations (AALZ)
- Air Conditioners, Central Cooling (ACAV)
- Air Conditioners, Packaged Terminal (ACKZ)
- Air Conditioners, Room (ACOT)
- Heat Pumps (AGUX)
NNational Electrical CodeandNECare registered trademarks of the National Fire Protection Association, Inc., Quincy, MA 02269. This reprinted material is not the official position of the National Fire Protection Association, which is represented only by the standard in its entirety.
Read more by J. Philip Simmons