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I might have the need to get an another air conditioner. Problem is I no longer have any additional space for another breaker in my main panel. I would like to know if it's safe to add another breaker on the same line for the other air conditioner? Something like the diagram below.

enter image description here

UPDATE:

My apologies for the lack of information. Currently my setup is similar to the diagram below but remove the first air conditioner.

The first 30 amp in the diagram is the 30 amp breaker in the main panel. Then there's another 30 amp breaker at the end before it goes to the air conditioning unit. This is how the electrician/installer did it. Although I think the 2nd breaker is not necessary.

We use 220V here and 30amps for outlets. I believe the wires are gauge 10. The current air conditioner is a 1HP non-inverter. Planning on adding a 2.5HP air conditioner.

UPDATE: 06/04/2020

Uploading image of the first A/C unit.

enter image description here

I don't have any info on the 2nd A/C yet as I don't have it yet. Haven't decided what to get yet but initially I wanted to get something with 2.5HP as I need to cool a 30 sqm room.

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  • I think you need to describe your current situation a little bit more. Also what's the difference between the "30amp" thing on the left, and the "30amp" thing in the middle? Jun 2 '20 at 2:28
  • What gauge is the existing wiring to the existing air conditioner disconnect, and is it run using a cable or as individual wires in conduit? Can you post a photo of the inside of the air conditioner disconnect box, even, please? Jun 2 '20 at 2:42
  • Also, can you please post photos of the nameplates on the air conditioners, or provide us with specsheets or make/model# information for them for that matter? Jun 2 '20 at 16:57
  • Definitely need the name and model, the FLA or RLA Listed on the unit. Is this a window unit or mini split? I am guessing dedicated plugin window unit and in that case if a 30 amp breaker was required for start up wired with #12 wire no you could not add, possible sub panel if 120v 10 gauge wire , but plug in device doubtful , need more info.
    – Ed Beal
    Jun 2 '20 at 17:28
  • Where are you on this planet? Can you get us specification sheets for the air conditioners in question? Jun 3 '20 at 11:49
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Ummm, no, you cannot do this and there is no purpose it in anyway. I'm going to guess that you have a dedicated 30A circuit for your 120V A/C unit. That means that there is no more than 30A available on this circuit and the installed A/C needs that amount.

If you try to add another A/C on the same circuit (all code concerns aside) you will still only have the 30A available and there will not be enough available to power the 2nd unit. So anytime both are operating the breaker will open.

What you need is a NEW 30A line from another 30A breaker in your box. You mentioned that your box is full and that's a problem.

I suggest here that you need the services of a qualified electrician to see if the current box can be reorganized to free up some space for another circuit. Otherwise the solution is likely to include upgrading your box to a new one that has more room.

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  • You're ignoring that the AC disconnect can be replaced with a subpanel, especially if the existing 30A AC circuit is run in conduit (which'd likely allow the wiring to be upsized). Jun 2 '20 at 16:40
  • This will be a problem as the wires are inside concrete walls. Adding a new line would mean I would have to chip off concrete from the main panel up to the location of the a/c for the new line to go to. Although I agree that this would be the best way, just hoping there's another easier route.
    – ads
    Jul 2 '20 at 6:43
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Well, I'm relying on what you are claiming, even though it seems like it would not be legal. (the dubious thing is allowing a 1-horsepower air conditioner on a 30A plug).

However, if these appliances are allowed on 30A circuits, then the numbers check out just fine. 3.5 horsepower is well within the capacity of a 220V/30A circuit.

The two breakers in a string do not make any sense. The only thing I can think is that one of them has some supplemental ability such as AFCI or GFCI (RCD). If so, this should be wired so the added air conditioner is also under that protection.

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  • The electrician/installer informed me that adding a second breaker would give additional protection to the A/C unit. That's all he said. I was hesitant at first but the engineer (in charge of the house construction ) agreed with the him so I went ahead with it.
    – ads
    Jun 4 '20 at 8:53
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    @ank Okay. It could well be something "lost in translation", e.g. they know exactly what they are doing but you or I are having trouble communicating/understanding it... if 2 pros are all for it, leave it lol... Jun 4 '20 at 13:42
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jwh20 is right, especially about the electrician.

However, if your breaker is DESIGNED to allow connecting two feeds, you may be able to run a second line off the existing 30-Amp breaker to power the second AC unit (local codes may override NEC minimum requirements).

Another however ... you can check the ratings of your AC units; they may both be OK on one breaker if their combined load is less than 30 amps. They may cause lights on the same circuit to dim, especially when they start, and if they both kick on at the same time, they might overload the breaker.

Have your electrician consider both those options.

UPDATE: I’m too new to comment on answers, so I’m limited to editing this one, but my response is still relevant to this answer, too. Breakers do not provide capacity; they limit flow (“current”, “amps”) before overheating occurs (all electric flow generates heat; too much flow means too much heat and possible damage or fire).

GFI’s add a sensor that detects when there’s a “leak”, say when there’s an unintended connection via water in a device that’s not waterproof or maybe a frayed wire makes contact with something or maybe a nail is driven through a wire, but there’s not enough additional flow to trip the overload trigger. AFI’s monitor the waveforms for telltale patterns that indicate arcing. Both trip well before too much heat is generated, the condition that traditional breakers already protect against.

Your nameplate shows max current (flow) of roughly 5 amps; that should occur for short time as it kicks on. It then settles to about 3 amps. You could in theory run 5 identical units off your 30-amp breaker. (Heat does not disappear immediately, so running 6 would likely cause nuisance tripping).

Another breaker between would add almost nothing for protection, since the original breaker will always see as much or more current and likely trip first. With a dead short, the two would “race” to trip first. The exception would be if the short were at the end of the line and the mid-line breaker tripped first, your first unit would still have power.

If the mid-line breaker were smaller, it might be more likely to trip first for a fault. It would likely trip first on smaller overloads or if the load happened to be less than 30 but more than the smaller breaker, the 30 would likely not trip (all breakers can mis-operate)

Regardless, a second breaker serves too little purpose if you’re not wanting to make it a “sub panel” and run thinner wire by using a smaller breaker.

The other comments about cooling capacity and latent vs sensible heat are spot-on; you want the units to run “long enough” before cycling. So there’s a good chance you’ll be ok adding the second unit.

But let a knowledgeable, qualified person look at your entire situation! Use this and other answers and comments to make sure your pro isn’t less than you need.

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  • Local codes probably would not override NEC they are normally stricter or eliminate a segment of code. As far as motor loads there are all kinds of rules we don’t know what the ac unit requires what size wiring lots of possible things here but more info is needed.
    – Ed Beal
    Jun 2 '20 at 17:19
  • You are correct, of course; I had in my mind (but not in my post) that local codes would likely only exceed NEC. They cannot relax any NEC requirements. Poor choice of words; thanks for clarifying!
    – pdtcaskey
    Jun 2 '20 at 17:24
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    They do relax by eliminating sections , even GFCI and AFCI requirements are exempted in my state for issues like motor loads or loads known to cause problems, so they exempt that section but when it comes to the ampacity tables I have not seen exemptions there those have massive amounts of data backing them.
    – Ed Beal
    Jun 2 '20 at 17:41

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