Electrical question, non-RV

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Boonieman

Boonieman

Well-known member
Joined
Feb 19, 2017
Posts
382
Location
Meade County, Ky
  Since this is a general question forum, I have an electrical question for the real electricians on here. Today, I installed 5 120v/15 amp receptacles in the pole barn. I?m not licensed, but I?ve done a lot of electrical work here and am comfortable with it and have a pretty good understanding of it.
  I installed the receptacles and the last thing I did was install a 20 amp GFCI to protect the downstream receptacles. Turned on the breaker and the GFCI would not reset. Disconnected the load side of the GFCI and left line side hooked up, GFCI reset and held. Tested continuity between positive and the grounds and neutrals and got zero. Continuity between grounds and neutrals tested good. Tried hooking the GFCI back up, would not reset. Unhooked load side again, GFCI reset and held. With the GFCI reset, I used pliers and touched the white neutral wire to the load side neutral screw on the GFCI, the GFCI immediately tripped.
  I inspected each receptacle and saw that on one of them, the bare copper ground wire on one of them was touching a neutral screw of one of the receptacles. ( I was using #12 wire so it was tight pushing all those wires into the boxes.) I corrected it so the grounds werent touching anything and now the GFCI is working normally.
  If I hadn?t been using a ground fault I?m sure this circuit would have worked fine. I just can?t wrap my head around why the GFCI would trip when the ground wire touched the neutral. It was the third receptacle in series after the ground fault.
 
Boonieman said:
  If I hadn?t been using a ground fault I?m sure this circuit would have worked fine. I just can?t wrap my head around why the GFCI would trip when the ground wire touched the neutral. It was the third receptacle in series after the ground fault.
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I am a retired union electrician so I will attempt an answer for you. The neutral wire is bonded to the ground back in the main panel.
 
  I understand that, but I don?t understand the difference in the path for the neutral and the ground since they go to the same place, and why the GFCI would have recognized it, especially since nothing was plugged into any of the new receptacles, so it just doesn?t seem to me it had a complete electrical path. Forgive my ignorance.


 
Boonieman said:
  I understand that, but I don?t understand the difference in the path for the neutral and the ground since they go to the same place, and why the GFCI would have recognized it, especially since nothing was plugged into any of the new receptacles, so it just doesn?t seem to me it had a complete electrical path. Forgive my ignorance.
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You are not ignorant and neither is your question. Asking questions is the only reason for online forums to exist. The GFI has a coil around the hot wire and a coil around the neutral wire. The current flowing in each wire is measured. Basically the amount of amperage travelling to the receptacles must equal the amount of amperage returning to the receptacle. If there is a difference of more than .05 millamps (?) then that means there is a leak somewhere and the GFI trips. What is going on upstream of the GFI has no effect on the operation of the GFI.
 
You said the bare ground wire was touching one of the white neutral screws in one of the boxes. The GFCI was doing it's job. It "saw" a "ground-fault" which is what GFCI stands for, ground fault circuit interrupter. It was interrupting the circuit by tripping.
 
The problem is we all understand DC very well. and in a DC world the Safety Ground and Neutral would indeed be identical and no current will flow unless somethig is plugged in and turned on

BUT in the world of AC.. Current flows (micro current) in the wire all the time and with the short you had TWO ground paths. or two neutral paths, and the GFCI sensed that.    This is one of the things that can be very confusing.. But in an AC circuit where wires lie side by side or are twisted together.. CURRENT ALWAYS FLOWS so long as the circuit is live.. Too small for even your watt meter to notice unless you left it plugged in for like a week and then you might see it (the old style teh disc woudl have turned slightly) but it's always there ALWAYS. The longer the wire, or wieres, the greater the current. 5 outlets around a garage I'd have to do some serious math but that's enough to trip a GFCI.

Oh two wires twisted together (or laying side by side) the term we use in elecctroni9cs is a "Gimick" Capacitor, and we do actually use them in Radio Receivers. and such to provide feedback.
 
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