Run two AC systems on 30A circuit (adding mini-split)
]IGo through the load calculation (use applicable code such as National Electric Code or any city supplement) to see if the two AC units can coexist on the 30 amp 8 gauge aluminum circuit.
There is (or should be) a nameplate or sticker inside or on the back of each AC unit that specifies the power requirements and power draw.
If the calculation comes out okay then you may put a sub-subpanel in place of the first AC unit's disconnect.
This sub-subpanel needs only the ground wire accompanying the 8 gauge feed since it is in the same building as the main panel. (A subpanel in a separate building from its feeding panel needs ground rods or other appropriate grounding electrodes as well as a ground wire accompanying the feed.)
YOu may be able to use a slow-trip 30 amp breaker at the 125 amp subpanel so if both AC units start at the same time you don't get a trip. A slow trip breaker might not be disallowed by code but it is not an outright substitute for failing the load calculation.
(A "sub-subpanel" is wired in the same fashion as a subpanel including with grounds and neutrals separated, and with grounding electrode(s) if it is the first panel in a separate building. "Sub-subpanel" is not official electrical terminology.)
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Last edited by AllanJ; 05-24-2012 at 07:39 AM.