Dedicated Line Noise Filter?

I assume neutral and safety ground are not connected together at the sub-panel, which would be a definite code violation and would create numerous potential safety hazards, and possibly noise problems as well. Given that assumption, the main purpose of a safety ground is defeated by the approach you've described. Especially if there is a significant distance between the ground rods of the two panels, and/or the soil in between them is dry.

@almarg , Now I'm confused and will call the electrician tomorrow. As I understand it, the hot for the subpanel is connected to the main circuit panel. The neutral and safety ground are connected to the subpanel.
The main panel has a 8' grounding rod into the earth, the subpanel has a ground rod into earth about 3 feet away.

Here's what I can confirm; using only the amp and preamp plugged into the same dedicated line, I get loud 60Hz hum when I power on the Atma-Sphere UV-1 preamp. When using a cheater-plug, I hear low-level hum. This happens on both receptacles/dedicated lines.
I have also used cheater-plugs on both components. BTW, no sources or power conditioners are being used.

I checked for continuity with a multimeter between chassis and IEC connector safety-ground pin and connection is OK. Performed this on both the amp and preamp.
This SE preamp has always caused hum with every amp I own. This is the noise/hum that I've been hearing.

almarg 7,350 posts07-15-2017 1:27pm

The sub-panel is connected by the hot lead and has it’s own ground including a second grounding rod.

Lowrider, my understanding is that a sub-panel should have hot, neutral, and safety ground all wired back to the main service panel, and safety ground (which may or may not be connected from the sub-panel to earth) should only be connected to neutral at the main panel, and NOT at the sub-panel.

Al, you are correct.
The sub panel feeder Hot/s, neutral, and safety equipment ground conductor are all fed from the same main panel.

An Aux earth ground connection, example ground rod, can be installed and connected to the equipment ground bar in the sub panel in addition to the equipment grounding conductor. Again, in addition to the equipment grounding conductor from the main electrical panel, the sub panel is fed from. (I personally do not recommend the addition of an Aux earth ground. Lightning loves them.)

The sub panel feeder neutral conductor/neutral bar can not be bonded, connected to the sub panel metal enclosure or the equipment ground bar. The feeder neutral bar must be left isolated/insulated from the metal sub panel enclosure. (Green bonding screw or neutral bonding strap that came with the panel discarded.)
If the the feeder neutral conductor/neutral bar is bonded to the enclosure/equipment grounding conductor/equipment ground bar then the equipment grounding conductor will be connected in parallel with the feeder neutral conductor. What happens then is the equipment grounding conductor will carry neutral current back to the main electrical panel, or where the service neutral is bonded, connected to the enclose, equipment ground, and earth. Not good for the equipment grounding conductor to carry neutral current.

@lowrider57
IF you feel confident with yourself looking inside the sub panel I can guide you through things to look for. Something that may be wrong with the way the sub panel is wired.

1) Do you have a multi meter?

2) Is the sub panel wired for straight 120V or 120/240V?
What is the approx distance the sub panel is from the main panel, it is fed from?
Any idea what size the feeder wires are?
What size is the breaker, in the main panel, that feeds the sub panel?

3) Turn off the breaker at the main electrical panel that feeds the sub panel.

4) Verify the sub panel is dead. You can check for voltage at the dedicated circuits outlets first. Use the meter, audio equipment, or a table lamp.

5) Remove the panel cover from the sub panel.

6) Verify 100% the sub panel is dead, de-energized. Use your meter set to auto AC volts or an AC voltage scale above the known voltage feeding the panel.
Locate the feeder wires, conductors, and with the meter verify they are dead.

7) What you should see.

Feeder wires that enter the sub panel.
If 120V only,
1 Hot conductor
1 White color neutral conductor
1 equipment grounding conductor

If 120/240V,
2 Hot conductors
1 white neutral conductor
1 equipment grounding conductor.

*One of the two above must exist. If Not post back. Do not go any further.

Hot feeder wire/s, conductor/s connected to the bus/s of the sub panel, or connected to a main breaker installed in the sub panel. Single pole for 120V, 2 pole for 240V.

You will see a neutral bar, with white color insulated wires that connect to it.
You should see the feeder neutral conductor, white in color, connected to the bar. You should also see the dedicated branch circuit white color neutral wires also connected to the bar. The bar should be mounted to a factory installed insulating material. Usually the insulator is black in color.
Look closely at the neutral bar, (or possibly 2 neutral bars that may be mounted on each side of the 2 Hot bus and circuit breakers), for a green colored screw head that is made to bond, connect, the neutral bar to the metal panel enclosure. If you see one IT MUST BE REMOVED. Remove the bonding screw and discard. Next look for any other wire or metal strap that may be bonding the neutral bar to the metal panel enclosure. If you see one REMOVE IT and discard.

No bare wires or green color equipment ground wires should be connected to the neutral bar. Only neutral wires can be connected to the neutral bar of a sub panel.

Next thing to look for is the equipment ground bar. It should be mounted/secured directly to the metal panel enclosure. You should see the feeder equipment grounding conductor connected to the bar. The wire may be bare, green in color, or have green marking tape wrapped around the insulation of the wire. You also should see the bare equipment grounding conductor, wires, of your Romex dedicated branch circuits connected to the ground bar.
If the electrician installed an Aux earth driven ground rod you will see the ground wire, from the ground rod, connected to the equipment ground bar as well. (Again an Aux ground rod serves no real purpose and may do more harm than good. Especially in the event of a lightning storm.)

Any questions?

@lowrider57,

On second thought, if you see the green bonding screw on the neutral bar or a bonding strap connected to the neutral bar that is connected to the metal enclosure, do not remove it.

Post back what you find. Do not change anything in the panel.

Just post back what you see.

@jea48 , Thank you so much for taking the time to share what I consider expert advise and knowledge.
I'm going to email your information to the electrician and we'll find out what is really going on. (I'm hoping that I'm wrong about how the subpanel is wired).
And @almarg , you're always a key resource for any audio issues I have.
 
What do you fellas think is the issue with the Atma-Sphere preamp (single ended)? It has always caused hum in my system.
It is designed with star-grounding and I confirmed that the safety ground is tied to the chassis. (also confirmed the grounding on the amp). This hum (which sounds like a ground-loop) has been constant even during the time I had the original dedicated line. Before that, I had a Rogue pre with no issues.
Your thoughts?

did you get construction permits for this project? Was the work inspected by your town's electrical inspector?

@cleeds , I just noticed your post. In Philadelphia, a permit is not required for an electrical addition or upgrade in a residence.
The law states that an inspection is required at the time a house is being sold.