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

The ground and neutral should only come into contact at 1 place in your home, at the service entrance.

If this is anywhere else then this is bad.  Check the N to G voltages on your circuit with everything disconnected.  Should be zero.

Also, check the usual suspects.  Did you also introduce or mess with a coax cable to a set top box or modem?

No coax in the house. I turned off any fluorescent lights. I checked the buzz with my piano tuner. 60hz. Have tried two different amps, same result.

Here is a pic of the electrical panel. I color coded it. Yellow is the coming wire. Black hot. White is neutral. Green is ground.

 

As Erik expressed, somewhere within your system you are picking up the ground noise. Try a plug cheater adapter to lift the ground just to see if hum goes away.

If that does not help, try disconnecting cabling that comes from other sources outside your new dedicated line.

ozzy

Are you sure that no component connected to your system is plugged into an AC outlet other than on this dedicated circuit? That could create a ground loop through interconnect cables.

Winner Winner Chicken Dinner!  Ground loop…duh!  I had the stereo rack plugged into the new, dedicated circuit, but I had the subwoofer plugged into a separate outlet that was not on the same circuit. Moved the subwoofer over to the dedicated circuit and…viola… no hmmm. Thanks all!  

Should the ground wire go to the block with the green screws instead of the neutral strip?

OP:

The bare wire from the main panel is the ground.  It seems to be connected to the buss on the left.  The white wire from the panel appears to be connected to the bus on the right. 

Keep that separation.

Post removed 

Looking at the picture, the ground and neutral from upstream were wired to the bus on the right.

If an electrician did this, get a new one.

I color coded it. Yellow is the coming wire. Black hot. White is neutral. Green is ground.

 

Forget the color-coding. Competent electrical people can figure it out with a simple text label.

 

This is how it should be done.

 

And just what do have that requires 20A continuous / 200A peak?

OP: I just ran some 12-2 from a new 20 amp breaker and installed a dedicated outlet for my system.

No congratulations. You did a very dangerous installation. For safety, disconnect your new subpanel from power until you reconfigure it the right way.

NB: I didn’t install the sub panel; I just added an additional breaker.  The sub panel has been in for almost a decade.  I have an electrician look it all over and correct as necessary.  Thanks all.

Call a licensed electrician. My brother, the E.R. nurse, makes his living off of amateur electricians and guys whose last words were "Hold my beer and watch this".

Make sure the sparky who comes to your home is the license holder & not an unsupervised apprentice or journeyman, as is often the case here in D.C.

As others have said, after turning off power to sub-panel AT MAIN PANEL, run the bare copper ground to the bus on the left of the panel and attach all grounds to this bus. Also make sure there is no bond strap between neutral and ground bus (the big twisted bare wires?). 

 

This is because if you lose the neutral between the two panels for any reason and the ground is attached or bonded to neutral bus, the ground wires back to the assorted circuits could then become hot. This only applies to sub-panels, not to main panels where the ground and the service connect are a short distance (hopefully) from the panel. 

 

Also, you said the wire is 12-2. Either you meant 12-2 w/ ground, 12-3 or you have no ground with your new circuit. Plus remember the red wire is hot along with the black for your combined incoming 240 VAC. 

At 60Hz it's clearly an earth loop.  These can be frustrating to locate.

1.   Plug a completely different system into the outlet you are using.  Is the hum still there?  Then it's the house supply.

2.   Strip down your system as far as possible and see if the hum is still there.  If so, substitute items in turn with outside items, including power cords, connecting leads.  Eventually the hum will be absent and you will have found the offending item.

If his sub panel was installed years ago, isolating neutral did not apply at the time.

Welp, I thought this requirement was a lot older, but per this discussion, 1999 was when the requirement changed:

 

 

Also, while we are at it, looks like you have mixed brands of breakers in there.  The breakers have to be either of the same manufacturer as your panel or specifically rated to be in that panel. 

Make sure you use cover plates for any holes in the cover.

/Possible ground loop. Do you have a digital processor? Try cheat plugs on different components. 

mjjw: "The sub panel has been in for almost a decade."

The panel is illegal.

Insurance companies love illegal and uninspected installations 🤑

 

 

 

@mjjw,

IMG_3400.JPG Sub Panel

You say its been that way for 10 years. Hard to believe it was installed and wired a qualified licensed electrician. I don’t think it was done by an licensed electrician.

How far is the sub panel from the main electrical service panel? Just a guess next to it or fairly close.

From the photo of the panel you provided the feeder wire from the main panel is only 3 wire. 2 black hot, (ungrounded), conductors that feed the 2 pole 100A main breaker in the panel and a bare stranded conductor for the neutral as well is being used for the equipment grounding conductor.

The sub panel should have been fed with 4 conductors.

Two hot (ungrounded conductors)

One white insulated neutral (grounded) conductor.

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.)

I assume the sub panel was install because the main panel was full. Three 120V circuits were moved from the main panel to the new sub panel. I assume, hopefully, to free up two breaker spaces in the main panel for a 2 pole breaker to feed the sub panel. Also just a guess two breakers spaces were needed for what ever the 2 pole 50 amp breaker in the sub panel is feeding.

(Would need a photo of the inside of the main panel to verify how the new panel was fed. The guy may have tapped the service entrance conductors ahead of the main breaker to feed the new panel. If that is the case then the panel would not be a sub panel.)

You might want to have a licensed electrician look at what you have and straighten it out... Make it right.

.

Separate the grounds and the neutral. Ground to the left side bar and the neutral to the right side bar. I'm an electrician and get called a lot for these corrections. 

EDIT:

Jea48 said:

I assume the sub panel was install because the main panel was full. Three 120V circuits were moved from the main panel to the new sub panel. I assume, hopefully, to free up two breaker spaces in the main panel for a 2 pole breaker to feed the sub panel.

Add.  Evidence would be a two pole breaker in the main panel that feeds the sub panel. Might even be marked on the panel schedule.

 

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.

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 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.)

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:
 

 

 

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.

@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?

@erik_squires

I am not sure how far back the NEC allowed metal conduit to be used as an equipment grounding conductor. The earliest NEC I have is 1971.

1971 NEC 250.91 (B). Types of equipment grounding conductors.

(1) Copper conductor or other corrosion-resistant conductor ... more wording solid, stranded ect... Nothing said specifically about the use of Aluminum conductor.

(2) Rigid Metal Conduit

(3) Electrical Metallic Tubing (EMT)

(4) Flexible metal conduit approved for the purpose, .......

(5) Armor of Type AC metal-clad cable

(6) The sheath of Type MI cable

(7) The sheath of Type ALS cable

(8) other ......

/ / / /

From earlier post:

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:

This was not a complete list of all the types of equipment grounding conductors allowed. I just stopped at #5.....

.

Separate the grounds and the neutral. Ground to the left side bar and the neutral to the right side bar. I’m an electrician and get called a lot for these corrections.

@guamie

What are you going to about the feeder bare aluminum neutral conductor? ...... (The Grounded Conductor).

I can see where it is touching the metal panel enclosure in several places. It is also in contact with the feeder metal conduit from the main service panel. An electrical hazard? No... Still not right though... Not if it is a sub panel anyway. We are assuming it is though...

The OP is not qualified to do anything in the panel. And apparently the OP has left the building because he hasn’t responded to questions...

.

@jea48 I believe you.  I was probably confounding the local code requirements with the NEC.  My mistake.

Edit to my above post. 🔼 🔼 🔼

Looking at the photo again this morning of the feeder conduit entering on the left side of the panel it may very well be PVC conduit. Not metal conduit. If that is the case the OP should not move the EGC ground wires to the ground bar on the left side of the panel.

I based the possibility the feeder conduit may be PVC by looking at what can be seen of the connector’s color of the threads and the poor image of the connector on the outside of the panel enclosure. I also based my possible conclusion on the 50A branch circuit load conduit exiting the top right side of the panel is PVC. 100% sure the feeder conduit is PVC? NO... Without knowing for sure it would be bad advice, imo, to move the EGC ground wires to the ground bar on the left side of the panel.

IF the feeder conduit is PVC the ground fault current path is to the feeder neutral bar/conductor. Moving the EGC ground wires to the ground bar on the left side of the panel, the ground fault current path would be through the panel metal enclosure to parts of the touching places where the bare aluminum feeder neutral conductors is in poor contact with the panel enclosure. A very poor low impedance connection to say the least...

 

Looking at the photo again this morning of the feeder conduit entering on the left side of the panel it may very well be PVC conduit.

 

I concur looking at the color, saturation and reflectivity of the visible threads. It's a very close match to the PVC exit.

 

Just returned from a long trip.  Want to thank everyone for the useful info.  I'm sorry I was not able to post more detailed pictures sooner.

Here are detailed pictures of both panels.  The conduit between the panels is indeed PVC.

Let me know if your thoughts.

 

@mjjw

It’s an easy fix for a licensed electrician.

Replace the bare Aluminum neutral conductor with an insulated #2 AL conductor. (Code required for a sub panel)

Install a new #8 copper green insulated equipment grounding conductor. He will terminate it on the ground bar in the sub panel. (Could be #8 bare solid but stranded is easier to work with. He’ll use a piece of green stranded #8cu insulated wire.

Move the equipment ground wires from the neutral bar to the equipment ground bar. (Extend wires as needed)

I would have the electrician check the System Ground, Grounding Electrode System, (Electrical Service connection to Mother Earth), to make sure it meets the code for your city.

.

Post removed 

Replace the bare Aluminum neutral conductor with an insulated #2 AL conductor. (Code required for a sub panel)

Edit for clarification:

Replace the bare Aluminum neutral conductor with an insulated conductor.

(Code required for a sub panel)

#2 AL size for the 100A feeder that feeds the sub panel. (sized per NEC)

.