Home A/C Wiring Question

I have a two year old A/C compressor. They wired it with 10/2 with ground to my inside 125A box. The outside box is 200A and has space for more breakers. When the a/c comes on my lights dim slightly. I can run the line for the compressor to the outside 200A box. My question is, would this be any better? Would it help at all with the dimming? Should I run it with larger guage wire? (13 seer, 2 ton(I think)) Should it be 3 wire (with ground) or is the 2 (using bare as common) that they wired ok?
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If the 125 has a substantial load on it, including the lights in question dimming would be expected and would very likely be diminished by connecting directly to the main panel, unless the entire 200 amp service is already near capacity. They didn't use bare as common, they used it as ground which is proper. If the run of cable isn't to long and the condenser doesn't draw more than 24 amps, the cable size is fine

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What is the minimium circuit ampacity of your outdoor uint and the max. breaker size as listed on the rating plate label? What kind of amperage is your unit drawing on start up and after it has run for a few minutes? Is your run capacitor good and did you test it for full uf capacity. Do you have a start capacitor? (Did it test ok?) Do you have a start relay? ( Did it test ok?) Are all your electrical connections starting at your compressor terminals and ending at your main panel: Good? Tight? Clean? Properly sized? Now tell me what is wrong. Bubba
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Everything electrical should be grounded. 10/2 is usually 3 wires, one of which is bare or ground. The other two wires carry the 240v load. "Common" is not the correct term for a/c distribution.
Wire should be sized to the load and distance. I can not answer your question http://www.electrician.com/vd_calculator.html
If the lights are dimming I would begin by checking all of the electrical connections. Then measuring the voltage at the service with a decent VOM meter. Do any of your neighbors have the same problem? If so then may be call the power company. There is a slight chance that they have anything to do with the problem.
Hard to say what is wrong with out seeing the installation.
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