HVAC - MCA/MOCPD - 334.80 Redtag

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James@AmericanGrit

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Oklahoma City, Oklahoma
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Residential Electrician
I am in OKC, Oklahoma, and I am having an issue here with my AHJ regarding MCA and MOCPD in regards to AC units.

Mike has several videos throughout the years pertaining to this issue and I have learned a lot from them.

When there is a nameplate, the job is pretty easy...IMO

In This situation, I have a 8-2 NMB installed on a 50A breaker at the panel.
Nameplate rating MCA 22.3 MOCPD 50A. I got this information late and played what i thought was a safe call.

I have referred my AHJ to article 240.4(G), which refers to 440, parts lll and Vl.

They have no desire to hear our point of view. They simply refer to 334.80, my understanding is that 440 relieves us from the ampacity constraint here on the conductors.

Has anyone won this debate in writing, anyone have a clearer code path than I?

I am being told that it explicitly that I have no chance here by the chief electrical inspector. I have made they changes they asked for due to not wanting to hold up the project. This isn't me trying to cheap out, its me trying to now prove the chief wrong. Thanks in advance
 
I'm afraid you are incorrect on this. Nothing changes the fact that NM has to use the 60 deg column. 240.4(G) or 440, doesn't give an exemption to use NM at 75 deg.
 
but..... he is using the NM at (actually below) it's ampacity) MCA 22.8
I fail to see the violation...
 
James@AmericanGrit said:
In This situation, I have a 8-2 NMB installed on a 50A breaker at the panel.
Nameplate rating MCA 22.3 MOCPD 50A. I got this information late and played what i thought was a safe call.
Click to expand...
You could have #10 NM cable with the 50 amp OCPD for this application. Even #12 MC cable would be code compliant with a 50 amp OCPD.
 
LarryFine said:
Isn't a disco required at the unit? If it's fused, is the home run a feeder?

I know we've discussed it a lot, but I don't recall reaching a consensus.
Click to expand...
Yes a disconnect is required at the unit unless the branch circuit device is within sight. I don't think there ever was a consensus to the feeder v. branch circuit argument but as of yet I see no mention of a fused disconnect in this thread.
 
LarryFine said:
Isn't a disco required at the unit? If it's fused, is the home run a feeder?

I know we've discussed it a lot, but I don't recall reaching a consensus.
Click to expand...
It doesn't matter...440 sends you to 430 for feeders, and when you do the feeder calcs for a single motor it comes out identical to a branch circuit for that same motor.
 
It should be a fairy basic concept for an inspector or AHJ. There are a number of on-line articles that explain it and there is this Forum, of course, if you can get them to do a but of research but seemingly you have an uphill battle.
 
OKC should have a electrical board.
Get on the agenda lay it out for them and ask for a decision.
This will help educate them.

Give the construction industry board a call. They will help.
 

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Also note that the MOCP is the MAXIMUM OC, you can go smaller, just not larger. At a 22.3 MCA, a 40A CB would probably be fine. Pass the inspection, then if the 40 nuisance trips, put the 50 back in.
 
Ask him to read 440.35 which sends him to 440.4(B)

If that don't do it go to the board.
Do every one there a favor.
Jraef said:
Also note that the MOCP is the MAXIMUM OC, you can go smaller, just not larger. At a 22.3 MCA, a 40A CB would probably be fine. Pass the inspection, then if the 40 nuisance trips, put the 50 back in.
Click to expand...
If the 40 trips ( doubtful) give the owner the inspectors number.
Agree 40 most likely be fine.

Have to wonder what size of conductor is in the whip. #10🤔
 
don_resqcapt19 said:
It doesn't matter...440 sends you to 430 for feeders, and when you do the feeder calcs for a single motor it comes out identical to a branch circuit for that same motor.
Click to expand...
So what you're saying is that the feeder OCPD can be larger than the ampere rating of the conductors?
 
Mike Burleson is on that board in OKC. Contact him. I used to have problems every time with John O. when he inspected my work. This sounds like some of his work. Good luck. If David Adcock is still the chief electrical inspector there, he could straighten this out for you also.
 
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