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Old 01-22-2011, 12:14 AM   #1
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sub panel grounding

I've got a question, and I hope that I explain this right...

My house has a 3 breaker box directly under the electrical meter on the side of the house. One breaker is a 30amp breaker that feeds only the electric clothes dryer. Another is a 40amp breaker that feeds only the air conditioner compressor on the outside of the house. The other is a 60amp breaker that feeds the breaker box in the house.

Originally, the breaker box in the house was only being fed one 110v feed from the main box outside. I have since run a 6-3 (w/ground) from the main outside the house to the breaker box in the house. I have separated the neutral and ground inside the breaker box in the house since technically this would be considered a sub-panel (correct?). I only have around a 35 amp draw on the breaker box in the house with all the lights and appliances on since the dryer is on another circuit, the A/C compressor is on another circuit, and the stove and water heater are both gas.

During my rewire of the breaker box in the house, I started to discover with my volt meter that some of my neutral wires showed a connection with ground wire even with all the wires disconnected inside the breaker box. (ie, the wire feeding the receptacle where the satellite receiver is plugged into, even with the neutral of that wire disconnected, still shows a connection to the ground feed wire from the main box outside, even without the ground wire being connected to the ground bus inside the breaker box inside the hosue).

One in particular is the circuit that feeds the receptacle that the air handler plugs into inside the closet where the air handler is located. I had the air handler completely unplugged from the receptacle, along with the ground wire that connected to the main box outside (again, the neutral and ground are not connected inside the breaker box in the house).

I am nearly positive that the ground of the air handler is also picking up the ground via the copper lines from the compressor outside, which is on a circuit independent of the breaker box in the house which is where the air handler derives it's power from.

Is this normal? Is this just an accepted way of dealing with a ground loop, or do I need to re-wire things to where the air handler is on the same feed as the compressor back to the main box outside the house to eliminate a double ground?

I hope this made a bit of sense...


Last edited by bcarl; 01-22-2011 at 12:26 AM.
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Old 01-22-2011, 12:23 AM   #2
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Part 2...

The other circuit in the house breaker box that I found was also making a connection to the ground wire with the wires not connected in the breaker box was the circuit that has my satellite receiver.

The dish outside is grounded to the metal conduit that is connected to the breaker box outside just under the electric meter. The ground (from what I can gather) can also flow through the outside sheath on the coax back into my house, to the sat receiver, through the receptacle, to the ground bar in the house break box, and back to the main box outside where the ground and neutral are bonded.

Should I disconnect the ground from the dish outside, and let the ground come through the coax sheath to the receiver, and ultimately ground through the circuit connected to the inside breaker box? Or is this another double ground I will need to live with?


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Old 01-22-2011, 08:24 AM   #3
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Grounding may appear to be redundant. The ground wires are not current-carrying. It's normal to find a unit appears to be "grounded" even with its ground wire disconnected, such as the furnace, etc. I would not worry about that.

The Neutral wire is a current-carrying conductor, however. Unless you have disconnected everything at the source, you may have false readings indicating ground-fault conditions on your neutral conductor, since they are connected together at the service panel.

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Old 01-22-2011, 09:03 AM   #4
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Except for certain electronic connections, double grounding is not a problem Just be sure that neutral is not connected to ground except at the main disconnect (in your case the box under the meter) that is, with the first breaker or disconnect downstream of the meter for each feed or circuit.)

You can leave the satellite dish grounded as it is unless reception improves with one or more "redundant" grounds removed.

I am led to believe that, when electronics engineers say a "ground loop" or redundant ground is causing a problem, improving the bonding or adding yet another interconnecting (or daisy chained) ground line that is bonded better will cure the problem just as well as removing all except one ground interconnection.

Once in awhile a complaint is made that the cable box fried my TV or my electrical system fried the cable company's equipment. I believe tthat connecting a bare wire from the stud on the TV or your own cable box where the cable screws on and with the other end connected to a known ground will nearly eliminate that problem.

With a properly connected system (ground and neutral connected (bonded) at the main disconnect) you will always measure continuity (nearly zero ohms) between ground and neutral anywhere in your system. To tell if ground and neutral are connected elsewhere (which is incorrect), do it one branch circuit at a time by unhooking the neutral for the branch circuit from the panel terminal strip and then measuring continuity between ground and that neutral end. While you are at it, be sure that all the neutrals and grounds are screwed down onto the terminal strip firmly although not with tremendous arm twisting.

Proper non-bonding of neutral and ground in a subpanel is then determined by unhooking the white wire going up to the main panel or main disconnect location and checking continuity between neutral and ground. This is usually difficult for a large subpanel because the white wire is quite fat. Instead visual inspection is more customary and considered good enough..

With no continuity (or fault or unwanted bonding) between ground and neutral up in a branch circuit, there will not be current incorrectly using ground as an alternate route back to the panel.
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Last edited by AllanJ; 01-22-2011 at 09:23 AM.
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Old 01-23-2011, 10:37 PM   #5
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Thanks guys for the help! I've got some more wiring to fix, and I'll put all the advice given into play.
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