Insecure Ground Connection or Neutral or ???

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  #1  
Old 05-15-11, 10:45 AM
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Insecure Ground Connection or Neutral or ???

An unusual problem has developed on a 15A 120v circuit servicing my Family room (7 receps and a ceiling fan). Two receps on the opposite side of the room from each other have surge suppresors plugged into them and then a stereo receiver in one and a LCD TV in the other. The surge suppressors have two green LED's. One indicates the "Protection" circuitry is working, the other green LED indicates "Grounded". Yesterday afternoon, I noticed that the "Grounded" LED on both was dimly lit and flickering. I took one of the suppressors and plugged into another circuit in another room. Both LED's were brightly lit. Then returned it to the Family room and again it was dimly lit. Approx. 1 hour later both LED's were brightly lit so I forgot about them. I spent all evening in that room watching TV----never noticed any dimming or brightning of the lamps or TV picture. Also failed to note how the suppresors were lit.

This morning, I again observed the Ground LED dimly lit, then bright, etc. I also observed that if someone turned on the microwave (on a different circuit and also on the other line or phase from the POCO) the Ground LED would immediately dim and even extinguish when the microwave was in use. I plugged in one of those 3 LED circuit testors in the Family room circuit and it indicated all normal with no changes when the suppresor LED's were dimmed. I took the surge suppressor and plugged it into the same circuit as the microwave and both LED's remained brightly lit even when the microwave was in use.

I have five identical surge suppressors plugged into various cirucuit all over the house. The LED's remain brightly lit on them. It appears only the one 15a circuit is affected.
The house is 21 years old and wired with copper wire in thinwall conduit. (32 circuits). 1 - 220 v circuit feeding air conditoner. Breaker not "on" yet this season.

Tomorrow I will pull the receps and check for loose connections and change any backstabbed connections to more secure methods.

Is this a less than secure conduit ground somewhere on the one circuit?? Or possibly an insecure neutral on the circuit? Or what??

Thanks in advance for any suggestions.

BOb
 
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  #2  
Old 05-15-11, 11:30 AM
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Unless you live in Chicago, or some other location which requires EMT to be run, I find it odd that a 21 year old house is run in thin wall. Most cases it would be run in Romex.

If this is wired in EMT you can check voltage with a meter between hot to ground, and neutral to ground, to see if there is anything not right.
 
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Old 05-15-11, 04:52 PM
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I'd suspect a loose setscrew, locknut, or self-grounding clip. He's in Illonois, so there is probably a conduit code.
 
  #4  
Old 05-15-11, 05:05 PM
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Yes I live about 50 miles southwest of Chicago. There were two builders in my subdivision. My builder used thinwall in all his homes. The other builder used Romex. I will take voltage measurements tomorrow and post the results and also tighten conduit set screws that I can get to on that circuit.

Bob
 
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Old 05-16-11, 04:49 PM
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Just curious, was your home wired with all conduit grounds or are there ground wires pulled in the conduits?
 
  #6  
Old 05-16-11, 06:24 PM
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The conduit provides the ground. No ground wire pulled through the conduit.

Bob
 
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Old 05-16-11, 06:39 PM
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I was able to take voltage readings today. Hot to Neutral 124.0 Vac. Hot to Ground 123.1 Vac. These readings did not fluctuate even though the "ground LED" was dim, then bright, etc.
I also took readings on several other circuits in the house with similar results. The Hot to Ground reading was always approx. 1 volt less than the Hot to Neutral reading. Measurement were taken with a Fluke Digital Multimeter.
I followed the conduit from the breaker panel to the first device (the recep that the TV and suppresor are plugged into). I tightened all set screws etc. that I can get to but the ground LED's are still dimming and going bright only on this circuit. Next, I plan on jumpering between another conduit and the conduit in question to see if that will affect the LED's.
I could also try running a ground wire through the conduit from the breaker panel to the first device. Any reason why I should not do this??

If that doesn't help, I am stumped.

Bob
 
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Old 05-16-11, 08:17 PM
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I could also try running a ground wire through the conduit from the breaker panel to the first device. Any reason why I should not do this??
No that is OK. In fact some electricians routinely include a ground wire.
 
  #9  
Old 05-16-11, 08:33 PM
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I'm not an electrician (I often do play one on weekends) and I never use conduit as the sole equipment grounding method. In your case I would look seriously at the neutral-equipment ground bond in the service panel and especially the condition of the bond between the conduit in question and the service panel.
 
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Old 05-17-11, 12:57 PM
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It could also be a bad connection in the receptacle, either with the ground pin or the bonding strap connecting the receptacle to the box.
 
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Old 05-17-11, 05:41 PM
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I would look seriously at the neutral-equipment ground bond in the service panel and especially the condition of the bond between the conduit in question and the service panel.
I have to agree with Furd on this one. Is the panel box painted gray? Is the conduit in question entering the panel box through a concentric knockout? It could be that your problem could be solved simply by adding a bonding bushing on the conduit fitting in question where it enters the panel and running a grounding conductor from the bonding bushing to the ground or neutral bar.

Like #5 from T&B

http://tnb-canada.com/en/catalogues/...gs_01u_eng.pdf
 
  #12  
Old 05-24-11, 05:56 AM
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Update. Yesterday I ran a 14 gauge green conductor through the conduit from the panel to the first recep. (This recep has one of the surge suppressors). I bonded the ground to the recep box and pigtailed to the recep. I tightened the hot and neutral connections to the recep and at the panel for this circuit.
The "grounded" LED's still dim and go normally bright on this circuit only. I discovered while doing this that is circuit uses a shared neutral and the other circuit is on the other phase of the incoming line from the POCO. I could change this to a dedicated neutral but since I am noticing no degradation in the service to this room I am inclined to chalk it off as a peculiarity. Any comments or suggestions ???

Bob
 
  #13  
Old 05-24-11, 06:50 AM
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Put a 100wat incandescent test lamp between hot and neutral, then hot and ground. If there is a brightness change, you have a problem. 10 second test.
 
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