A/C wire size.

[Jaybone812]

I would set a lower bar, especially for HVAC techs who are allowed to install wiring and may not do any voltage drop calculations. If they said "I'm leaving expansion in case they go to a 5 ton with a 41A MCA and this cable is sufficient for that", it should be fine for a much smaller unit. It also happens when you remove a system that had a larger wire than you need now with a unit that is more efficient and has a lower MCA. No need to rip out a cable when the old system with a 30A cable that was sized fine now has a 15A unit on that same wiring.

And I’d never question or look twice if an existing feed ended up being oversized because for a newer more efficient unit . My thought process would apply to new installs in situations like guys thinking when sizing the ocpd for hvac equipment they have to size it in accordance with 240.4(d)(1-8)- match wire to breaker . That’s the type lack of knowledge and I’m not letting them use the exception
Common sense and real world scenario would always factor in because if you have it on your truck and it’s bought and paid for you’ll use the larger feed to save the money .


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[nibowenr5]

Just to confirm, because I'm in a similar scenario as OP and continue to get conflicting answers. Installing HVAC with 38.8A MCA and 60A Max Overcurrent Protection. That should allow 6 AWG wire on a 60 amp breaker correct?

 

[Dennis Alwon]

Just to confirm, because I'm in a similar scenario as OP and continue to get conflicting answers. Installing HVAC with 38.8A MCA and 60A Max Overcurrent Protection. That should allow 6 AWG wire on a 60 amp breaker correct?

It would allow a #8 on a 60 amp breaker. Assuming we are talking copper. The HVAC unit has overload protection that will protect the wires. The breaker is for ground fault and short circuit only

 

[Strathead]

The exception references 250.4 which discusses an effective ground fault current path.
The effectiveness of that path is a long discussed topic (See Soares Book on Grounding as an example).
IMO, the reference to a "qualified person" in the exception would be someone like a P.E. with expertise in grounding,

I don't agree with that. Elsewhere in the code, at least in the past it has stated things like, "under engineering supervision". Code definition

Qualified Person. One who has skills and knowledge related to
the construction and operation of the electrical equipment and
installations and has received safety training to recognize and
avoid the hazards involved. (CMP—l)

 

[TX+ MASTER#4544]

Just to confirm, because I'm in a similar scenario as OP and continue to get conflicting answers. Installing HVAC with 38.8A MCA and 60A Max Overcurrent Protection. That should allow 6 AWG wire on a 60 amp breaker correct?

2023 NEC TX
440.21General
You can use the nameplate to size the conductors and the OCPD or the branch circuit selection current.

Remember, if the name plate calls for a fuse for OCPD, then you can't use a circuit breaker, unless it conforms to the following listed below.
You could have three correct alternate wiring methods for conforming to the Code.
You can use fused disconnect, a non fused disconnect or a circuit breaker.

440.32 Single Motor Compressor (1) (2) Use the greater of the two.
A hermetic refrigerant motor compressor is considered to be a continuous load.
Check out Section 440.14 Location for something new about the disconnect.
440.22(A) Exception No.1 and No.2 a minimum or a maximum OCPD rating.
440.11 General Notice the shaded text (a change from the previous NEC edition).

Thanks for reading
Comments accepted
TX+MASTER#4544

 

[mtnelect]

This might help to explain.

 

[tortuga]

If your selected ungrounded conductor could be protected by a larger fuse or inverse time breaker than your using and the folowing conditions apply;

• The circuit is 200A or less
• 208V - 600V nominal
• 50/60 HZ,
• A grounded system,
• Less than or equal to 250' in length

I'd say qualified persons would agree its safe to select the largest breaker size that would apply to the ungrounded conductor and select the corresponding minimum equipment ground size for that breaker in 250.122.