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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
asvjerry's avatar
asvjerry
4,263 posts
 

@ieales ...*L*  What to run?

Whatever boats his floats.... ;)

clearthinker's avatar
clearthinker
1,582 posts
 

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.

invalid
1,073 posts
 

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

erik_squires
15,640 posts
 

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

 

 

erik_squires
15,640 posts
 

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.

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