A/C Electrical Install

Hiya Folks, I'm planning on pulling a permit to install a branch circuit to drive a new refrigerated A/C compressor. Before I go to the inspector's office I'd like your opinions on my plan.
I currently have a 125A (rated) panel feeding the house with a 100A Main breaker. I plan to check the feeders on this to see if I can bump the Main up to a 125A breaker. I can change a few breaker's around and get room for a 220 double breaker. I should be ok from a total amperage standpoint as I don't use the dryer circuit and am on a gas range but by bumping up to the 125A, I'd be able to leave those intact, I believe. The electrical specs on the compressor say the RLA (Rated Load Amps) is 20.2, the LRA (Locked Rotor Amps) is 137 A, the Fuse or HACR Breaker Min is 35 A and Max is 45 A. I figure I'll put in a 40 A/220V breaker and run a 6/3 THHN feeder via conduit to the location of the compressor approx. 40 ft. away. I understand I could probably use 8/3 but just in case I ever want to upsize, I figure the extra cost of the 6/3 is minimal for the length of run. The feeder would terminate in a fused disconnect mounted on a unistrut frame with Double Element fuses sized at 175% of RLA (Time Delay fuses) so they would be 35 A. From there, I'd continue with the feeder to the equipment via flex. Does this sound like I'm on the right track? I still have to figure what size conduit (1/2" would prolly work as there will minimal 90's but 3/4 might just be easier to deal with) and I'm still a little shaky on the fuse size. I didn't count the Fan Motor Full Load Amps (1.2A) so that would move the fuse up to 37.45A so I'd probably have to stick with the 35A fuses. Am I figuring this correctly?
I've given myself a headache searching all the articles in the codebook but hope I'm on the right track here. Ultimately, the inspector will be the judge but I appreciate any advice you may have. Cheers, cc
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James "Cubby" Culbertson writes:

If you're not using the amperage for dryer or range, I wouldn't bother upgrading the main. Mothball the circuits, and do the upgrade later if you revert those appliances to electric.
I would not depend on the inspector to check all the analysis.
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put thin breakers in if you have too, to keep the unused dryer and stove lines intact for a future home sale 100 amp should be OK.....
IUf you upgrade your service go to 200 amps
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I agree. I really don't want wires hanging around so to speak. I'm not so sure on the 100A service though. My biggest concern is in addition to the 40A A/C unit, the other "large" appliance is a 3hp. cabinet saw and my well pump. I haven't gotten out there to measure up or even pull the panel cover yet so who knows what I'll come up with!

That would be ideal, and expensive. I'm not sure the feeders from the transformer at the street are sized for 200A which would mean a pretty expensive run of wire not to mention the whole new load center. At this moment, I'm trying to stretch this one as far as I can safely until I build my shop. At that point, the house will in essence become a subpanel and the main power will be feeding from the shop. I of course probably won't be building a shop for a few years but that's the plan at the moment now. Cheers, cc
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for permit, electrician, parts, inspection. Electric company was no charge for up to 400 feet and I'm only 150 feet from transformer. So, check with your electric company. Might not be as expensive as you think. Electric company has incentive to provide a way for you to use more of their product.
Bob
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All situations are different, but in NY your garden variety overhead 200 amp service goes for $2000-$2500

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charged that much here, we'd still be using candles.
Bob
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Wow! I can't imagine getting that for under a grand. My feed into the house is underground and I'm not sure how much they'd charge to upgrade that if necessary. I may pop off the panel cover today and see if I can read the feeder size into the panel. Upgrading would sure make a lot of sense but I just can't see spending a fortune on it right now. Cheers, cc
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You may want to contact the utility company regarding an upgrade. If the utility company "owns" the wires feeding your meter, they may elect to leave them at whatever size they are and just allow you to increase the size from the meter into your panel and upgrade the main breaker

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it's cheaper to upgrade to a 200A service than it would be to buy a main breaker and the 220V/40A breaker. I've never changed out a full panel before and I take it kind of slow when doing electrical so not sure I can pull off the upgrade myself without being in the dark for a night :) Cheers, cc
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Put a junction box on the dryer circuit, and run it from there to the AC. Take off the dryer socket. Sounds like he's gonna need 10 wire, and 30 amp breaker for the outdoor unit.
What did you read in the book that came with the unit? What wire size, and breaker does the book reccomend?
--

Christopher A. Young
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I haven't got the unit yet just what I found on the web from the Mfg. A 30 A is too small according to the Mfg. (mentioned the Min size as 35A in my OP). Cheers, cc
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I wouldn't bother with the 125 amp main unless you found you needed it, and the wire size probably wouldn't take it. Use larger conduit than you think you need. You'll need a mortgage right now for the wire, and I wouldn't bother with a fused disconnect, unless a local code requires it, just use a 60 amp pullout. The 40 amp main will protect it as per the specs

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a nightmare. As well, my code doesn't require a fused disconnect so the pullout style might just be the way to go. Cheers, cc
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