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If your hum is really getting into the guitar pickup, and it sounds like that's the case, the noise is going "though the air" and no sort of ground wire type solution is going to make any difference. Your problem is magnetic fields, not grounding.
Short of modifying the guitar with more shielding, or using a different guitar, or trying to put more space between the guitar and the offending wires, about the only solution I can offer is to have an electrician rewire the problem electrical circuits, tightly twisting the hot and neutral conductors. This will tend to make the hum field cancel out, which should reduce the noise level by quite a lot. I don't know if this is really a practical option for you, but it would probably work.
The hum field is generated by current through the power wires. Perhaps you can also get the noise level down by plugging your gear and appliances into different outlets or circuits. Turn off everything in your place except for bare minimum stuff you need on in order to monitor the noise. If it is lower, then start turning things back on one by one, to see which devices are the offenders. Of course, the real problem might be caused by something in a neighboring apartment, but at least you can got some answers by doing that test. Kaplan Electric in North Hollywood is very studio savvy. Good luck!
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