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Hum in Speakers with New Dedicated 20 amp Circuit

I just ran some 12-2 from a new 20 amp breaker and installed a dedicated outlet for my system. Now I get a very audible hum in both channels. If I switch back to the shared 15 amp outlet, no hum. I checked the new outlet with a tester and it checks out as wired correctly. At the electrical box, the black wire is connected to the breaker and the white and ground are attached to the same ground strip. I’m using a 20 amp receptacle.

Anyone with thoughts on how to resolve?

mjjw
erik_squires
15,663 posts
 

 

One equipment grounding conductor. (Note: If a steel conduit is used between the main panel and sub panel that meets NEC for use as an equipment grounding conductor.)

That's a surprise! We can't do this for junction boxes or outlets.

ieales's avatar
ieales
1,201 posts
 

I haven’t checked the code in a while, but I think it’s because a panel is more or less permanent.

With an outlet, if it’s out of the box, no earth. Gotta protect the unskilled from themselves.

jea48
4,268 posts
 

 

jea48 said:

One equipment grounding conductor. (Note: If a steel conduit is used between the main panel and sub panel that meets NEC for use as an equipment grounding conductor.)

erik_squires said:

That's a surprise! We can't do this for junction boxes or outlets.

 

Yes you can. NEC 250.118 (2) (3) (4)

 

250.118 Types of Equipment Grounding Conductors
 

The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

  1. A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
  2. Rigid metal conduit.
  3. Intermediate metal conduit.
  4. Electrical metallic tubing.
  5. Listed flexible metal conduit meeting all the following conditions:
 

 

 

kingsleuy
173 posts
 

Just checking the situation.

Pictured is your new breaker is on the bottom right.  Outputs to a separate box with a new outlet in your room.  You did your switching inside the house between the old and new outlets without touching inside the breaker box?

I would try moving your new breaker to the slot just above it.  Get on the other phase.

Being nosey.  The 50 amp breakers goes to your Tesla charger?

I would like to see inside the main panel.  Where we are getting the feeds from. Looks like they come in from the lower right.  Hots goes to the 100 amp breaker top left two.  The stranded aluminum cable going to the neutral buss, top right. 

What I don't see is a neutral cable terminating On the neutral buss.   No, zero  wires on the ground buss. And more copper ground wires on the Neutral buss. Leads me to believe the that ground cable is carrying both ground and neutral.  I would not sign off on this box.

erik_squires
15,663 posts
 

@jea48 from decades ago, I thought I had learned that metal conduit alone wasn’t good enough due to likelihood of the conduit being imperfectly connected or becoming disconnected vs. ground wires.

Now I am wondering if this was something local to Massachusetts?

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