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?
EDIT: Jea48 said:
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. |
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. . |
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:
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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:
This was not a complete list of all the types of equipment grounding conductors allowed. I just stopped at #5..... . |
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... . |
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...
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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. . |
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) . |
