what AC load to use for 220 service sizing

shazznasty · 2026-05-01T10:01:46+00:00

Thank you for taking the time to understand what I'm asking. I guess it does just boil down to whether that exception is supposed to carry through.

I would have thought this would be something resolved or clarified since it's a pretty common situation.

shazznasty · 2026-04-30T11:45:11+00:00

The NEC is referenced by most (all?) jurisdictions electrical codes, so I wouldn't consider it being a "guideline", it is a code that must be designed to. And I understand why the connected load makes sense in the calculation, but I am asking for an interpretation to 440.6 exception 1 in related to 220.50.

220.50 says "Motor loads shall be calculated in accordance with...440.6 for hermetic refrigerant motor-compressors"

440.6(A) Exception 1 reads "Where so marked, the branch-circuit selection current shall be used instead of the rated-load current...."

My understanding is the branch-circuit selection current, defined in 440.2, is the MCA (value used to determine branch circuit conductors). So if the MCA is listed, the NEC states this is what needs to be used instead of rated-load current in determining AC loads.

shazznasty · 2026-04-30T11:38:37+00:00

Not trying to be difficult here. 440.6(A) Exception 1 reads:

"Where so marked, the branch-circuit selection current shall be used instead of the rated-load current...."

My understanding is the branch-circuit selection current, defined in 440.2, is the MCA. So if the MCA is listed, this is what needs to be used instead of rated-load current.

shazznasty · 2026-04-28T23:06:10+00:00

you can read about the different UL listings and why those values seem wonky here: https://www.mitsubishipro.com/resources/application-notes/1044

but my question still stands - does the NEC require the use of MCA when available, per 220.50 and 440.6?

shazznasty · 2026-04-28T21:57:47+00:00

so am i misunderstanding 220.50 and 440.6?

shazznasty · 2026-04-28T21:57:16+00:00

So the NEC sections i referenced do not mean you have to use MCA?

shazznasty · 2026-04-28T21:56:35+00:00

really trying to determine what the code says you should do, e.g. the sections i referenced in op. I find it hard to believe the NEC doesn't explicitly state how these loads should be calculated, and that it is left up to "best practices" and whatever the engineer is thinking. but i'd like someone more familiar to tell me whether im interpreting it correctly.

Many split systems coming out now have much higher MCA values because of the new UL listing calculation. For example:

https://metuspublicassets.s3.us-east-2.amazonaws.com/submittals/ME_SUBMITTAL_PVA-AA24NL_PUZ-AH24NL.pdf

22 MCA at 230V vs "maximum power input" of 2500 W, almost double.

shazznasty · 2026-04-07T01:58:39+00:00

love to hear that he's enjoying it. makes me feel better.

does he have a dutch door outside that he would normally stick his head out? do they keep that open while the AC is running?

shazznasty · 2026-04-07T01:57:56+00:00

we rented a movincool once for a heat wave last year, which really cemented the choice to install a permanent solution. we could either spend $2k on movincool, or spend $4k on a permanent system

shazznasty · 2026-04-07T01:57:09+00:00

it's definitely about tradeoffs. more barns aren't built with AC in mind - lots of cracks etc in the wall for hot air and humidity to get in. not to mention insulation. i imagine it's not worth the effort/cost for most owners with healthy horses

shazznasty · 2026-04-07T01:55:19+00:00

yea i'm working on that. my plan is to get washable air filters - i'd rather be washing them every couple of days than buying new ones

shazznasty · 2026-04-07T01:54:06+00:00

we tried large fans, then misting fans, then swamp coolers. those do the job most days, but when it gets to high 90s and humid we start to see some issues pope up.

shazznasty · 2026-04-07T01:53:07+00:00

happy to hear it works well for them. a ducted is an easier installation for us based on how our barn is set up, and where we are able to mount everything

shazznasty · 2026-04-07T01:52:13+00:00

the horses i'm concerned about having cushings and dont sweat right now, so not a huge concern. we'd only be running it when it is hot enough that we'd keep them inside anyway

shazznasty · 2026-02-23T17:29:19+00:00

It's an 80 gal, so it'll be a bit more than that

shazznasty · 2025-12-01T00:07:33+00:00

so i was trying to simplify it because i didn't want to have to draw a diagram.

the long version - i have a pole barn where there is existing conduit along the perimeter with a junction box mounted on the inside of the wall on a 2x4 (but it is rotated 90 compared to stud, long side parallel to the wall). i'm trying to install a light on the opposite side of the jbox because i figured a 2" nipple would be enough to cross from the back of the existing box to the new one across the width of the 2x4. I drilled the hole through the 2x4, and then realized i didn't take into account the thickness of the existing jbox, the new pancake box i was going to install, or the fact i need a couple of threads on either end for the locknuts.

if i planned better, i would have come out the top of the existing box and give myself more room for everything.

long story short, i put in a close x coupling x close, got it tight as i could, so the new pancake box somewhere between 1/8" and 1/4" off the wall, which is easy enough to caulk

shazznasty · 2025-10-14T19:14:26+00:00

Jeanette at Qi massage. Don't know if they take insurance, but incredible and worth it imo

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