Sizing wire and OCPD for HVAC/mini split systems

Crash117 said:
A word of caution here. If you run your 12 gauge conductors to a fused disconnect and use a 25 amp breaker in the panel you will be in violation. If you use a non fused disconnect you are covered just right.
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Explain why it’s a violation to used a fusible disconnect if he uses a 25 amp breaker and what code rule prohibits that


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Eddie702 said:
You can use a fused disconnect at the unit or an unfused disconnect if you have the correct breaker in the panel. The fuses could be 25 amp or larger unless the equipment is marked "fuses only"
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I’ve haven’t seen a condenser unit marked “fuse only “ when they only allow a fuse . It would be nice if they did include “only” it would provide clarity on the subject. When the manufacturer specifically calls for a fuse to provide the ground fault/short circuit protection. It’s just marked “max Fuse “ on the nameplate , instead of max ocpd, or Max Breaker/fuse or MOP etc


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clemver said:
I was always under the impression that both are sized per the nameplate specs. If I have a name plate that reads:

"Maximum overcurrent protective device - 25A"
"Minimum circuit ampacity - 18.1A"

That lets me put a 25A breaker in and I can run #12cu to the unit.

https://imgur.com/a/QJLSspP

I'm struggling to decode the code article that allows that to be done. (referencing 2023 code)

I see 440.22(c)
"...........the protective device rating shall not exceed the manufacturers values marked on the equipment"

But for conductor size all I see is 440.32
"Branch circuit conductors supplying a single motor-compressor shall have an ampacity not less than the greater of the following:
-125% of the motor-compressor rated-load current
-125% of the branch-circuit selection current

So can they be sized separately from the OCDP and off the MCA or do the conductors need to be sized at 125% of the RLA?
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I would run a #10.
 
infinity said:
It's a long winded argument that we've seen before. It starts with the Article 100 definition of a feeder.
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But the argument is falsified by 430.62(A), which says that the feeder OCPD for a feeder supplying one motor/HVAC branch circuit and no other loads may be sized the same as the branch circuit OCPD, when the feeder conductors are sized per 430.24, just like the branch circuit conductors are.

Cheers, Wayne
 
Eddie702 said:
You can use a fused disconnect at the unit or an unfused disconnect if you have the correct breaker in the panel. The fuses could be 25 amp or larger unless the equipment is marked "fuses only"
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I agree with you. Though I had an inspector one time that didn't see things that way. That was long enough ago I just did what he asked. Today I'd probably be getting out the code book and having a discussion with him. May or may not win the battle but am going to at least make him think about it.
 
wwhitney said:
Not true. Article 430 has the same allowances for a feeder supplying just one branch circuit as for the branch circuit itself.

Cheers, Wayne
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I was going to ask, but instead, I looked:

"430.22 Single Motor. Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating"

similar wording in 430.32 several motors. It doesn't say anything about feeders, or branch circuits, it says conductors.
 
Strathead said:
I was going to ask, but instead, I looked:

"430.22 Single Motor. Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating"

similar wording in 430.32 several motors. It doesn't say anything about feeders, or branch circuits, it says conductors.
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I would also ask what's the continuous duty application and is that applicable to an AC unit.
 
Strathead said:
I was going to ask, but instead, I looked:

"430.22 Single Motor. Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating"

similar wording in 430.32 several motors. It doesn't say anything about feeders, or branch circuits, it says conductors.
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Now skip further ahead to part V which is for feeders you are in the branch circuit section.
 
infinity said:
I would also ask what's the continuous duty application and is that applicable to an AC unit.
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I have always thought that all HVAC is a continuous load. But isn't it a fact that if you size motor conductors (or multi load equipment) compressors, fans, electric heat at 125% or by MCA that you don't have to add anything additional for continuous load?
 
Eddie702 said:
I have always thought that all HVAC is a continuous load. But isn't it a fact that if you size motor conductors (or multi load equipment) compressors, fans, electric heat at 125% or by MCA that you don't have to add anything additional for continuous load?
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No you do not consider whether or not this is a continuous load. The manufacturer has done all of the work with the information provided on the nameplate. Just use the number provided and you're good to go
 
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