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I am putting a couple mini split compressors. One needs 240v/15Amp, and two need 240v/60Amp.

The main line comes into the middle of the house. I have 125A breaker feeding a panel in the basement. The basement panel runs a 240v/20A outlet an older mini split runs on, as well as my office, and there is a dual 40A, I'm not sure if that's the dryer or not. Then I have 100A breaker feeding that primary runs my garage. I have a 20A going to two outlets for power tools, another 20A going to an outlet my freezer is on, and another 20A going to the outlet for my chopsaw and grinder. Then a 15A for lights, and another 15A that powers two outlets in the room on the other side of the garage wall.

The garage was wired up for a vet we had living with us, and he used it as a woodworking shop. He is no longer with us and the garage outlets don't get much use any longer.

The idea is that I'd put all 3 circuits in the garage box. The 15A and one of the 60A are pretty easy runs, 10ft along the garage wall, then punch them outside. The 15A will go right there with an AC Disconnect. The 60A will run another 30ft down the side of the house. I had an electrician say that he'd just tuck the wire up under the bottom edge of the aluminum siding.

First off, what wiring do I need for the 60A, 10/2? I figure 12/2 should be fine for the 15A.

Our house is almost 100yrs old, so we try not to have wires running all over the outside of the house, so I while I like the idea of "tucking it up under the bottom edge of the siding", is that kosher? It's going to go to an AC Disconnect, and figured it would need to be in conduit. I run a lot of networking cable and I know there are cables that are direct bury and can run outside w/o conduit, so maybe there is electrical cable like that too?

I really hope so, because the last outlet is WAY on the other side of the house, and it's an ugly run over two doorways, around several windows around several corners. Trying to do that in conduit will be a serious PITA.

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    Can you post photos of the panels involved please? Commented Nov 7, 2022 at 12:44
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    Question updated to reflect the 240V service OP has in Colorado, USA.
    – isherwood
    Commented Nov 7, 2022 at 15:22

2 Answers 2

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60A is a lot for a minisplit. Two of those? That's a huge amount. My AC compressor runs on a 25A breaker (originally a 30A fuse). I don't have a huge house, but for comparison that would mean your house needs on the order of 5 - 6 times the capacity. The only way that really makes sense to me is if there is significant resistive backup heating included in those values. If that's the case then the numbers make a little more sense. In any case, the nameplate ratings and/or manufacturer instructions are what matters.

The usual sizes are: 15A, 20A, 25A, 30A, 40A, 50A, 60A. So a 60A breaker would normally be required if a 50A breaker is not enough. Assuming continuous use derate requirement, that means something more than 40A each, plus we'll assume 12A for the 15A circuits. So no that's something over 92A continuous, which means you need a feed breaker/wire for 115A. Unfortunately, 115A > your current 100A feeder to the garage panel that you want to use. In addition, this will all likely push your entire house over the limit. Not clear whether 125A is your actual service or just one existing panel. If it is your actual service then forget about it, you need a heavy-up to do this safely. If is just the feed to one panel but your service is 200A then there is some possibility of making this work.

As far as wiring, assuming the service and panels can handle the load, there are some variables involved depending on the type of wire/cable and other factors, but I believe you need a minimum of either 6 AWG copper or 4 AWG aluminum. Aluminum is fine for this, but you need to check local codes to make sure it is permissible.

Heat pumps vary widely in efficiency. It may be that you have a huge house and this is the way to make it work (in which case, I really wonder what you used before). It may also be that you can find a much more efficient system that will both save energy and avoid the need for significant upgrades, which could easily pay for the increased cost of the system itself.

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Re:

I had an electrician say that he'd just tuck the wire up under the bottom edge of the aluminum siding.

Our house is almost 100yrs old, so we try not to have wires running all over the outside of the house, so I while I like the idea of "tucking it up under the bottom edge of the siding", is that kosher? It's going to go to an AC Disconnect, and figured it would need to be in conduit. I run a lot of networking cable and I know there are cables that are direct bury and can run outside w/o conduit, so maybe there is electrical cable like that too?

I believe the issue here is mechanical protection against damage as well as weather-tightness, so some sort of conduit seems a must. There are a number of types of conduit, including "liquidtite" plastic that might fit better esthetically, but of course you'll have to do the calculations on allowable fill to figure out minimum diameter.

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  • I love the liquidtite stuff, I've used it several other times. Pretty sure I'd need at least 3/4"
    – Dizzy49
    Commented Nov 8, 2022 at 16:37

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