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Old 11-24-2011, 09:00 AM   #1
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Strange grounding issue


I am not a professional electrician, but do have some basic concepts. My training is more with electronics.

So anyways on one branch of the house, I have replaced some receptacles. A few of them were in bad shape or not even grounded. This house is very old and some electrical components outdated.

For the branch in question, when I test for voltages, I get these -

H to N - 120
H to G - 75
N to G - 45

Here is the strange part - When the "Dish TV" box is plugged in, then I get these readings -

H to N - 120
H to G - 120
N to G - 0

These readings appear on all outlets of the branch. I have only to plug the dish TV box in to somehow "correct" the voltages.

All but one of the outlets on the branch have been replaced and wiring inspected. I don't know if the one I DIDN'T mess with yet is bad but if not, what would cause the weird readings until I plug in the dish TV box?

Lastly, one of the power strips plugged in to my room has a light for "ungrounded" that illuminates when I unplug the dish TV box (which is in another room, on another receptacle)

Also, to take readings, I am using a DMM. Is that a bad idea?

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Old 11-24-2011, 09:12 AM   #2
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Strange grounding issue


This is a classic case of knowing how to do the physical work, but not knowing the codes or details on what you are doing.

You say this is an old house? This means it is likely that much of the wiring does NOT contain a valid equipment ground. Yet, you went around and installed 3-prong grounding receptacles? BAD idea.

You are getting these readings because the dish system is likely properly connected to the houses grounding electrode system, which is directly connected to the house's electrical panel. So in by plugging in the dish system you are backfeeding the grounding of the receptacles. This can be a very bad thing if there is a fault to ground since the grounding path is so sketchy and with such low resistance. Having fault current on a grounding system like this could cause some VERY hot connections.

The ONLY legal and safe alternative to rewiring the branch circuits is to GFI protect these circuits and mark the receptacle "No equipment ground present".

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Old 11-24-2011, 09:59 AM   #3
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Strange grounding issue


It sounds like the grounds are 'bootlegged", ground connected to the neutral. Not a good thing. If you are using a digital meter the voltages you are seeing can be phantom readings. Plugging in the cable box adds a load to the circuit and the phantoms disappear.
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Old 11-24-2011, 09:59 AM   #4
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Strange grounding issue


Ok, some more details of this -
On this particular branch, two of the outlets had a ground connection, one of them did not have any (it was some old two-prong outlet) and one of the outlets appeared to have a broken ground connection (the one where the dish is plugged in)
So basically what i did ground-wise was add it to one of the outlets in the room, and re-connect the ground to the receptacle where it was broke.

In this house, some of the electrical was upgraded at some point but some was not. I can tell by the wiring in the basement. I did not do the previous upgrades. The two-prong outlet was basically falling apart and was not really safe to even use.

So is there a site where I could learn more about the proper way to ground the branches or at least know what has and hasn't been done in the past?

Also in the main electrical panel, yes, the grounds are connected to the neutral (not my doing, I didn't mess with anything in the breaker box.) none of the receptacles have neutral connected directly to the ground

Last edited by AnErin; 11-24-2011 at 11:12 AM.
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Old 11-24-2011, 11:45 AM   #5
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Strange grounding issue


That is the way to properly ground outlets. Use new wiring with a ground wire. And this needs to go back to the panel shared neutral/ground bar if a "main" panel or separate ground bar if a "subpanel".

Then a modern good ground system for the main panel would have a big copper wire going to two ground rods placed 6 ft. apart. Then a separate big copper wire to the metal water water pipe system (if you have metal).

Note that grounding used to be done only with a cold water pipe ground, but then plastic water pipe came along and that no longer was a good idea. Some people replace portions of their metal water pipe system with plastic, then their electric system is no longer properly grounded!!!!!

So also check your main grounding.
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Old 11-24-2011, 12:22 PM   #6
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Strange grounding issue


YOu can temporarily run a separate ground wire from the panel up to the receptacles in question, daisy chaining through the latter. It can follow the route of the circuit wires or cable precisely, somewhat, or vaguely.

Grounds and neutrals must not be interconnected up in the house within the branch circuits.

The 45 volt reading between neutral and ground up in the branch circuit means that somehow that portion of ground wiring is not connected solidly to anything. Your meter is reading phantom voltage or voltage via a bad (high resistance) connection betwen the portion of ground wiring in question and perhaps another ground wire where that portion should be connected.
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Old 11-24-2011, 12:30 PM   #7
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Strange grounding issue


from the wiring I CAN see, there doesn't appear to be any neutrals connected to grounds except back at the main panel.

OK next silly question about this - this branch has four receptacles, would each one need to have a separate ground back to the main panel or can the grounds be connected at some point before the panel?
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Old 11-24-2011, 12:31 PM   #8
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Strange grounding issue


The voltage you are presenting in your original post are indicating an open ground connection. The dish system is completing that gound to appear to correct the issue.
I think you are saying this is an old two wire circuit that someone has changed the two prong receptacles to three prong without adding the proper grounding. You should either replace the cable on this circuit with new three wire cables or run a gound wire to each recepacle. As I see if you can fish a gorund wire to each receptacle why not fish a new cable.
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Old 11-24-2011, 01:24 PM   #9
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Strange grounding issue


Quote:
Originally Posted by AnErin View Post
- this branch has four receptacles, would each one need to have a separate ground back to the main panel or can the grounds be connected at some point before the panel?
This is how I would do it. A single temporary ground wire would pass through or near each of the outlet boxes on the same circuit in turn (with pigtail to each intermediate receptacle) and then go down to the panel.

A receptacle or group of receptacles on a different circuit would have its own ground wire down to the panel.

If you know for a fact that some of the receptacles' yokes are bonded to each other (using the green screws) for example you yourself ran new Romex cable with ground among them but the old cable back to the panel was left as-is for now, then a temporary ground wire need go to just one of the receptacles in that group.

If these added ground wires first reach the big copper wire going to ground rods, they can be clamped on there there instead of going all the way to the panel.
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Last edited by AllanJ; 11-24-2011 at 06:31 PM.
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Old 11-24-2011, 03:21 PM   #10
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Strange grounding issue


For one circuit, you run one "romex cable" from the breaker panel to the first outlet, then a wire from there to the next outlet, and from there to another outlet, etc.

Then inside these boxes, you connect the grounds like any of the following...





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Old 11-24-2011, 08:45 PM   #11
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Strange grounding issue


Well I dug a bit more into it, and while the four receptacles have decent wiring and are easy to trace in the basement, it looks like the branch from the breaker box runs up into the attic. I know none of THAT wiring has been changed in God knows how long or what kind of grounding (if any) is up there so it looks like this is going to be a bigger project than I thought. The breaker that controls the branch is evidence of the wiring in question. I traced the wires, plus that circuit breaker controls a ceiling fan as well.

Last time I had to mess with any wiring in the attic (one of the closet sockets was bad) I remember bending the wire and the insulation wanting to crack. OLD wiring.

So I get to investigate the attic wiring as well

Good times....

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