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In my main panel I have a circuit where the hot wire is split within the panel.

Circuit in question

I was investigating this circuit because I am getting a hum from any speaker plugged into an outlet on the circuit. I saw this and I thought it looked odd. I'm wondering two things:

  1. Is the circuit, as shown, safe/recommended
  2. Could this be causing interference for devices on the circuit

The circuit is 9 receptacles and one single switched light, and the breaker is a twin (two 15amp in a horizontal configuration).

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  • It's not dangerous, but it's definitely non-standard, and it might not be to code (I'm not sure). From what little I know about audio electronics, I believe this could be causing your line interference. – BlueRaja - Danny Pflughoeft Feb 21 '14 at 23:51
  • 1
    A lot of things can cause the hum you are hearing. A non-constant voltage is a big one. That could be caused by audio equipment on a fully loaded circuit, dirty power coming in, and others. Might be worth plugging into a good quality surge protector that also does line filtering (not all do). Also, nine receptacles is a lot. I am not sure what the code says, but I hear six is a good upper bound. – user4302 Feb 22 '14 at 1:06
  • If that isn't where the neutral and grounding system connect, then yes this could cause hum. – Brad Gilbert Feb 22 '14 at 6:17
up vote 2 down vote accepted

Check that the receptacles are wired correctly and that the hot and neutrals aren't crossed. As far as diagram the only this I see odd about this is that right circuit the neutral and ground are connected to the same bus. They should be connected like that the circuit on the left. Since the two busses are eventually connected its not dangerous but it may cause a small ground loop and maybe causing the audio hum.

Also I assume you're plugging in a powered speaker. If the audio source is plugged into a different circuit especially if the circuit is the other phase improper grounding can cause a hum.

Let us know what resolved the problem for you.

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  • If this is the main service panel then neutral/ground are bonded and the buses are identical. if it's a sub panel then yes they should be on separate busses that are not connected – Steven Feb 22 '14 at 17:57
  • For the record, the hum was caused by having neutrals wired to the ground bus and/or grounds wired to the neutral bus. When I rewired so each type of wire went to the proper bus, the hum went away. I also rewired the phase wires so they were not joined in the panel, and, although it made me feel better, it had no effect on the hum. – Steve Mallory Mar 3 '14 at 15:41

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