GFCI Problem

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  #1  
Old 12-06-04, 12:24 AM
FredlyFX
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Unhappy GFCI Problem

I am in the process of wiring a shed I built in the back yard. I have installed a sub panel in the shed to distribute power. There is a GFCI in the main panel I am getting my power from. My problem is that when I was hooking up one of my circuts in the sub panel it tripped the GFCI when I touched the ground wire to the neutral bus. The hot and neutral hadn't even been connected yet, but as soon as I touched that ground wire on the bus the GFCI tripped. How could there be a ground fault if there is no power going to the circuit yet? Any suggestions on trouble shooting this would be greatly appreciated.

FredlyFX
 
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  #2  
Old 12-06-04, 05:40 AM
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Why was the GFCI providing power to the shed if you are still wiring the shed? Common sense says to kill the power to the shed until you have everything wired up.
 
  #3  
Old 12-06-04, 07:54 AM
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Your neutral bus should not be bonded to the ground in a sub panel. It sounds like it might be bonded still in this panel.
 
  #4  
Old 12-06-04, 08:23 AM
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My problem is that when I was hooking up one of my circuts in the sub panel it tripped the GFCI when I touched the ground wire to the neutral bus.
The solution is simple. Don't do that. This sounds like a variation of the "doctor, it hurts when I raise my arm" joke, but this is no joke. Grounds and neutrals are not meant to be interconnected except in the main panel.
 
  #5  
Old 12-06-04, 04:02 PM
FredlyFX
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I'm confused now. I have always put the ground and neutral on the same bus unless there was a seperate one provided in the panel. Should I take the grounds out of the neutral bus and just connect them all together & to the one coming from the house?

What's really confusing me in this problem is why there was any fault with ground? I had wired several plugs downstream, but there was no power to them at all. Why would it trip the GFCI to touch the ground wire to the bus?
 
  #6  
Old 12-06-04, 05:26 PM
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In a sub panel the neutral and the ground must be isolated. You must also make certain that the neutral does not connect with the metal box. The neutral must connect with nothing but the neutral wires from the circuits.

In order to figure out why the GFCI tripped, you are going to have to do a better job explaining just what you had hooked up at the time and how you had it hooked up.
 
  #7  
Old 12-06-04, 05:38 PM
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The GFCI works by detecting a difference in current between the hot and neutral wires. By connecting the ground and the neutral together some of the current went though the ground and not the neutral wire. The GFCI did its job of detecting a fault to ground and tripping.
 
  #8  
Old 12-06-04, 05:58 PM
FredlyFX
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I think I am figuring out now what my problem is, and there are a couple.

I am running the power from the house with a 10Ga extension cord for now. (I know it's wrong, but it will work for lights and a couple of plugs till I can get the trench and conduit done.) I installed a lone GFCI receptical at the main panel on the house on a 20 amp breaker. It then runs through the cord to a disconnect on the outside of the shed. (what I'm calling the disconect is a small box with 2 fuse type breakers and a large lever or switch on the side like is used on machinery. I only used one side of it) I ran a pig tail out of the disconnect and put a male plug on it to plug into my extension cord.

Inside the disconnect I have the ground connected to the can and the neutral just passing through to the sub panel inside. Inside the shed I have 3 circuits. One for lights, and 2 for plugs. At the time this issue arose I had the lights and one plug circut connected and running fine. It was when I started to connect the final plug circuit that I ran into trouble with the GFCI.

That final circuit has 3 double gang boxes connected to it with 2 standard 15A duplex recepticals in each. I had everthing connected and run back to the sub panel. It's all run with new 12ga romex. It was when I touched the ground to the bus that the GFCI tripped and I was in darkness. I figured that since there was no power to that circuit anywhere that it should not have tripped the GFCI.

I think that at this point I will remove all the grounds from the bus and connect them to the ground from the main panel. Hopefully that will solve it. Can you guys suggest any other possible solutions?

Thanks for all your help so far. I really appreciate it.
 

Last edited by FredlyFX; 12-06-04 at 11:44 PM.
  #9  
Old 12-06-04, 06:04 PM
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I am having trouble understabnding exactly what you did do, but I do know that it is not safe.

As was stated, your GFCI tripped because the current was not the same on the neutral as on the hot wire.
 
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