Originally Posted by gregzoll
Incorrect. Does not matter if both breakers are on the same leg if you are using 12/2. What matters is if you are using 12/3 for the two circuits, since both breakers have to be on opposite legs on the panel. Even if you have them on the same leg, using 12/2 you are not going to get hum on the system.
Hum is again caused by poor or incorrect grounding, or poorly maintained electrical systems, not whether breakers are on the same or opposite legs on a panel.
This is a lot of fun , with the OP not trusting a contractor he has hired , asking for help then taking shots at people who are trying to help , OP using wrong terminology to confuse things , and other posters confusing things further by not taking into account they are obviously communicating with someone who knows nothing about electrical systems .
As to the above quote , how do you feed the load from 2 breakers , same leg or different legs , with a 12/2 Romex ? are you suggesting using the bare ground for the neutral? There are 2 insulated wires ( black, white) and a bare ground in Romex , can't feed from 2 breakers in any configuration with 12/2. Now I am pretty sure you meant a 12/2 from each breaker
as opposed to using 12/3 Romex , but your above quote is confusing , and I'm sure more so for the uninitiated.
Any configuration of breakers , or Romex the OP has his contractor use that follows code will not inherently introduce hum . As you stated , the interference is introduced by poor connections , corroded connections or a short to ground . Occasionally a motor load will introduce interference or "hum" because of EMF , easiest way to avoid this in a home is to not have your electronics on the same circuit as any kitchen or laundry receptacles.
The exception to this is if the OP is running very sensitive testing equipment , and has multiple frequencies ( 50, 60 Htz.) running parallel , similar to signal wires run parallel to high voltage wires , then EMF can introduce hum into the systems , but I doubt that is the case , otherwise he would most likely be an electrical engineer and wouldn't be here asking the original question.
OP , tell him what your goals for power are , and either trust him or hire someone else. Explain you will want to test your AV setup for " hum" before signing off on the job. He should have no problem letting you test your gear to make sure there's no interference. Unless you hired him from the parking lot of Home Depot , you should be fine . Take a breath , relax and let the man work.