Gotcha, thanks Marc, I was thinking he meant it “had to be minimum”… duha.
We always use 10 ga on those but it’s good to know we could save a couple of dollars I suppose.
This one is a little more straight forward
8ga wire, 50 or 60a breaker
Joe
So what your post #20 says, Figure 2, in the text below, That a 40amp protective devise with a minimun wire sizes, awg#10, because the total amps are 27.5
**The Branch Circuit Requirements
**The branch-circuit conductor size requirements for hermetic refrigerant motor-compressors are located in Part D of Article 440. The sizing requirements for the branch-circuit conductors are very similar to those requirements for standard motors. Basically, the branch-circuit conductors are required to be sized at 125 percent of the rated-load current of the single hermetic motor-compressor or 125 percent of the branch-circuit selection current, whichever is less. However, for combination-load equipment having a nameplate as required by Section 440-4(b), the branch-circuit conductors are required to be "not less than the minimum circuit ampacity marked on the" nameplate of the equipment (see Figure 2). See NEC Section 440-35.
The manufacturer has already calculated the conductor size to be based on the total of all of the motor loads in the combination-load equipment times 125 percent. It is not necessary to do these calculations again. For this type of equipment, the installer and the inspector only have to install and verify that the branch-circuit conductors supplying the equipment have an ampacity equal to or greater than the minimum circuit ampacity marked on the nameplate of the equipment.
and …
The “maximum overcurrent protective device” rating is the other very important number on the data plate. The overcurrent protection device marked on combination-load equipment is marked “maximum” such as “maximum fuse size.” This means that specified size cannot be exceeded. The device could be less than that maximum size.
It may seem that the conductors are improperly protected. However it is the combination of the maximum size short-circuit and ground-fault protective device together with the overload protection system of the equipment that is providing the overcurrent protection for all circuit components. If the overload protection is field-installed for a hermetic refrigerant motor-compressor, the overload sizing must be in accordance with Section 440-52 and must not exceed the manufacturer’s values.
In Figure 2, the nameplate indicates the minimum circuit ampacity and the maximum overcurrent device. Based on the nameplate data the conductors are required to be capable of carrying 27.8 amperes. Remember, with combination-load equipment the 125 percent factor is already used by the manufacturer to determine the 27.8-ampere total. A No. 10 THWN copper conductor is an acceptable size for the circuit conductors. The maximum overcurrent protective device marked on the equipment is 40 amperes. It appears as though the No. 10 THWN conductors are improperly protected. This is not true. The 40-ampere fuse or HACR circuit breaker provides the short-circuit and ground-fault protection. The overload protective device limits the normal running current to the proscribed values.
The overcurrent protective device could be a device rated smaller than 40 amperes as long as it can handle the starting and running current of the equipment. These maximum values are often misunderstood to be the only size allowable by the* Code,* when in fact it is the value that must not be exceeded.
Joe
So nothing smaller than 10 awg wire, (12 or 14) correct? Thats because of the amp draw of 27.5, right. And the circuit breaker, nothing larger than a 40?
Please contact the IAEI for further clarification, I posted the reference for you, and I agree and do not question the author Michael Johnston.
Here’s another route you (we) can take directly to the people who write the rules.
An example:
**Question 2. **I am very confused on what inspectors of Riverside County, California, are asking for on A/C condensers (breakers size). For example, if the condenser plate reading has a minimum breaker size of 24 amps, and a maximum breaker size of 35 amps, and I install a 30-amp breaker size, am I in the wrong? Inspectors are telling me that I should go to the max on the breaker. Are they correct? I cannot find this section in the *NEC *1999. — F. A.
**Answer 2. **This is not a violation of the Code unless the nameplate of the unit specifies a minimum size fuse or circuit breaker greater than 30 amperes. Section 440.4(B) in the NEC 2002 applies to air-conditioning equipment that contains a hermetic refrigerant motor compressor and other equipment such as a fan motor. The Code does not require manufacturers to list minimum size overcurrent protective device sizes on the nameplate. The nameplate must only indicate the maximum rating of the fuse or circuit breaker.
If the manufacturer elects to specify a minimum size device on the nameplate, NEC 110.3(B) would require the installer to abide by the nameplate information. — Tom Garvey, CMP-11.
You can find additional information in the NECH and at www.bussmann.com
Joe
Inspector to Inspector, If the nameplate states, 27.5 amp draw, then the conductor needs be be greater than 12 awg? Thats all I am asking.
27.5 a is not that ambiguous, where it gets confusing is when the number is something like 23a that falls between the 240.4(D) and 310.16 rating (for #12). HVAC equipment makes this easier by actually giving you the max breaker size but in the case of a hardwired motor load you might have to do some pencil work to see if the breaker is appropriate. The general rule is the breaker can be 250% of the motor nameplate FLA and the wire size has to be 125% of FLA, using 310.16 rating and that might be at the 75c column if the motor has 75c lugs (and not wired with a cable wiring method like AC, NM or MC which limit you to 60c).
It might be noted that as soon as you put a plug on a motor you lose these concessions because a user can come along and plug anything into that receptacle. That is the reason why we have 240.4(D) (the 15a-14ga, 20a-12ga rule) The installer has no control over what a user might plug in so they build the 80% safety factor into the allowable breaker size. 14, 12 and 10 gauge wire is the most likely to end up on a receptacle.
Conductors sizes are continously printed along the wire. When looking at a short peice, you may not be able to see the size markings but the visible portion of the wires in a panel are usually long enough to be able to see the markings.
Not an inspector but you are correct. For a Air Conditioner a #12 would be maxed out at 25 amps.
The problem is when it is a cable. Individual conductors are usually not marked in cables, you need to see the cable jacket. That will usually be behind the drywall if this is a flush mounted panel.