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I have an old, small house where electrical was updated about 20 years ago.

Description of electrical hook up: I have the main power coming into the meter, with a panel box adjacent to the meter. It splits: one supply via a dual-pole (correct terminology?) 60 amp breaker to the garage sub panel and another supply via a dual-pole 60 amp breaker to the house sub panel. This house sub panel is fed by a thick wire (writing on the wire states "aa 8030 type se xhhw-2 style R... 2 AWG" and also says 4 AWG. The house sub-panel is rated for 125 Amps. There is currently a 50A dual pole, and various other breakers feeding circuits throughout the house. See below picture. The dryer, washer, and water heater are in the garage.

enter image description here

I am updating the labeling to match the circuits. There is possibly an unused circuit breaker as well (the ?). There are also two empty slots in the box.

Also, I know there is some rust on the box. This is not from rain, but rather heavy humidity.

Question: Can I hook up a split AC unit to this box? The unit states a 20 amp 220V breaker (so 20 amp dual pole?)

Updated photo of the data sheet for the panel below: enter image description here

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  • Can you tell us what kind of panel this is? Maybe a photo of the panel label? – Harper - Reinstate Monica Apr 21 '20 at 23:16
  • Yes, can you shoot us photos of the labels on all panels involved? (They'll be on the inside of the panel doors.) Also, what does the 50A breaker in the house panel control, and are the dryer and water heater gas or electric? – ThreePhaseEel Apr 21 '20 at 23:22
  • @ThreePhaseEel The 50A breaker feeds the range/oven. The dryer and water heater are electrical, but not part of this panel. They are in the garage. The panel shown is a Eaton Cutler-Hammer, 125 Amp Max. It is fed from a Cutler-Hammer as well (that contains the 60 amp breaker) – Pdhawaii Apr 22 '20 at 16:25
  • @Pdhawaii -- how many square feet of house does the house panel feed? Also, what's the minimum circuit ampacity on the air conditioner you're looking at, and what does that 20A breaker right below the range breaker feed? – ThreePhaseEel Apr 22 '20 at 22:47
  • @ThreePhaseEel The house feeds 1000 sq ft. That 20 amp breaker doesn't feed anything either, at least from what I can tell crawling in the attic, crawlspace, and trying every outlet/light in house. The AC unit states it requires a 20 amp dedicated breaker. Thanks for quick replies! – Pdhawaii Apr 23 '20 at 2:17
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You'll need to swap that BR260 in your garage panel for a BR290 to do this

Right now, given that the house panel serves 1000 ft2 at 3VA/ft2, as well as three small appliance branch circuits for the kitchen at 1500VA apiece, and an 8kVA allowance for your range, we plug those numbers into the standard Article 220 load calculation procedure and get about 52-53A of load on this panel out of it. Since your AC pulls 15A of nameplate current, we tack that on and get about 66-67A of load in the new configuration, too much for the existing 60A breaker.

However, the fact that your SER cable is 2AWG is the saving grace here. A 2AWG aluminum SER cable running between two pieces of distribution equipment with 75°C rated lugs is good for 90A; I suspect it was breakered at 60A simply because the electrician didn't have any breakers between 60A and 100A (or even simply above 60A) on their truck when they did the electrical update. So, we can free up some wiggle room here by swapping the BR260 in your garage panel for a BR290.

From there, you can fit a BR220 in the house panel (or a GFTCB220 if you want to be ready for the 2020 NEC's expanded GFCI requirements), and run 14/2 or 12/2 (your choice since the minimum circuit ampacity on your AC is 15A, and air conditioners use the Article 440 wire and breaker sizing rules, which say "follow the nameplate" for everything we're concerned with here) to the air conditioner disconnect box. You'll need to transition to individual THHNs of the same gauge in liquidtight or a prefabricated flex whip for the disconnect box to air conditioner connection, by the way.

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  • Ok great advice!! Any worry about unbalanced load with the BR290 next to a BR260 in the panel? – Pdhawaii Apr 26 '20 at 1:08
  • @Pdhawaii -- as in above/below, or across from each other? – ThreePhaseEel Apr 26 '20 at 2:00
  • Right next to each other. So itll be a 60 amp breaker feeding the garage, and now a 90 amp feeding the house. That's ok to have different sizes like that? – Pdhawaii Apr 26 '20 at 5:16
  • @Pdhawaii -- my main concern would be if they were across from each other, as then you could run into the stab ampacity limits on the main panel – ThreePhaseEel Apr 26 '20 at 12:47

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