Grounding Problem

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  #1  
Old 12-02-12, 08:58 AM
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Grounding Problem

We have a normal duplex outlet above the counter top near our sink. It is downstream from a GFCI outlet which protects this outlet. 12 Gauge Romex feeds this outlet, through a METAL box.

I wanted to replace the duplex outlet with another one that has a single outlet and USB power, so I pulled the old duplex outlet out and disconnected the black, white and ground wires. The electrical box is METAL, and I found it interesting that electrical tape was wrapped around the perimeter of the outlet, covering the heads of all the wire connection screws - including the ground screw.

When I connected the new outlet/USB, it works fine UNTIL I touch the outlet mounting screws to the metal box (?). I put the old outlet back in, and have the same problem. When the ground, black and white wires are attached, my receptacle tester shows an "OK" connection. But as soon as I attempt to screw the outlet to the metal box - and the screw touches the metal box, the GFCI trips.

I am at a loss as to what the problem is. It appears to be some sort of double grounding issue, but it occurs even when I attach the original outlet in the same manner as it was connected when it was working.

If I DON'T connect the outlet ground wire, and only use the mounting screws to ground the outlet to the metal box..... everything is fine and my receptacle tester shows an "OK" connection.

Any thoughts as to why the GFCI is tripping when both the Romex ground wire is connected to the outlet, AND the outlet is connected to the metal box (via metal screws?

Thanks in advance!
 
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Old 12-02-12, 09:19 AM
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Welcome to the forums!

Is the ground wire bonded to the metal box? How are the wires connected at the GFCI?
 
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Old 12-02-12, 09:22 AM
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The tape is usually put on to keep the screws in the side of the device from hitting the METAL box. No problems with that.

If you put your old outlet back in and now your GFI trips......it can only mean you put the wrong wires on the wrongs screws. White must be on silver screw or the large sized slot in the receptacle and black must be on the darker colored screw or the smaller sized slot. Ground on outlet frame.
 
  #4  
Old 12-02-12, 10:32 AM
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Is the ground wire bonded to the box as well? I suspect that it is not and it should be. When you connect the ground wire to the receptacle and then screw it into the box, the frame of the recp bonds the ground to the metal box. If one of those hot screws or wires makes a connection with the box, it shorts to ground and causes the GFCI to trip. Without the ground wire connected to the recp, the hot screw touching the box isn't able to short to ground. The remedy to this is to find out what is shorting to the box and prevent it form happening. You then need to bond the box to ground with its own ground screw.
 
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Old 12-02-12, 10:44 AM
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The ground wire is not bonded to the metal box. It comes in the back of the box (along with the black and white wires), and all three are connected to their respective screws on the duplex outlet.

What is strange is that my receptacle tester shows the wiring as "OK". It is only when I screw the duplex outlet to the metal box (as soon as the screw makes contact) that the GFCI trips??????
 
  #6  
Old 12-02-12, 10:54 AM
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The hot wire is shorting to the box somewhere. Inspect it to see if there are breaks in the insulation and make sure there isn't any exposed wire sticking out of the wire nuts.

If you keep mounting the the receptacle with the circuit live, you are going to get shocked.

The ground wire needs to be tied to the box.
 
  #7  
Old 12-02-12, 11:48 AM
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Have you checked too see if you voltage between the white conductor and the box,it almost seems that the box could be hot, a nicked hot wire hitting the ungrounded box, no ground no short ,breaker or fuse would not trip either.
 
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Old 12-02-12, 01:44 PM
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The ground wire is not bonded to the metal box. It comes in the back of the box (along with the black and white wires), and all three are connected to their respective screws on the duplex outlet.
Turn the power off at the breaker, remove the duplex receptacle, straighten all the wires and inspect the insulation carefully on the hot and the neutral. Repair any insulation problems. Install an approved ground screw - a green hex-head 10-32 machine screw - to permanently attach the ground wire to the box.Use a 3/8" nut driver to start the screw in one of the holes made for that in the back of the box, crimp the appropriate ground wire around the shank of the screw, clockwise, tighten the screw down, and splice any other ground wires and pigtails to the bonded wire. Put a cap on the hot wire and turn the power back on. Check to see if the GFCI will reset. If it will, uncap the hot wire and test for voltage from hot to neutral, ground and the box. Expect to see 120V each time.

If all of that tests OK, turn the power off and install the duplex receptacle. terminate the wires to the screws on the sides, not to any stab-in holes in the back. Crimp the wires around the appropriate screws, clockwise, and tighten all four brass and silver screws, plus the ground screw. Fold the wires into the box, mount the receptacle, and turn the power on again.

Then you can move on the the GFCI itself.
 
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Old 12-03-12, 05:50 AM
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Thanks for all the replies. I have straightened and checked the wires - and did not see any sign of exposed wire - but I'll try Nashkat's recommendations after work tonight!
 
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