"Extra" Ground Wire - Incorrect GFCI Circuit Wiring?

Reply

  #1  
Old 11-09-11, 01:33 PM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 6
"Extra" Ground Wire - Incorrect GFCI Circuit Wiring?

I'm in the process of troubleshooting a GFCI-tripping problem, and I have encountered an unexpected wiring condition that, although I don't think it's the source of my recent problem, seems questionable to me. I purchased the home "new" in 1995 and the circuit in question remains in an "as-built" condition. Until recently this circuit has been problem-free.

Best I can figure is that perhaps an electrician had a change of mind when wiring up the now-problemmatic GFCI circuit. I found that the last outlet box downstream of my "problem" GFCI had an "extra" piece of Romex cable pulled into the box. The hot wire was terminated with a wire nut (no voltage). The neutral wire had no wire nut and was left unterminated (also tested no voltage -- I capped it with a wire nut just to be safe). The ground wire, however, was connected to the ground wire from load side of the GFCI. I disconnected the "extra" ground wire from the load side ground, then tested the "extra" ground wire for continuity to ground on another circuit -- it's grounded.

Because the "extra" ground wire seems to be grounded elsewhere, I feel like I can only improve the stability of the GFCI circuit by permanently disconnecting the "extra" ground from the GFCI circuit (although it hasn't been an issue for the last sixteen years.) Similarly, I don't think I'm hurting anything by permanently disconnecting the extra ground wire, as it already seems to be grounded elsewhere and the GFCI circuit tests as grounded without it. Does this seem reasonable, or am I missing any circumstance that might suggest it would be safer to leave the "extra" ground wire connected to the GFCI circuit?
 
Sponsored Links
  #2  
Old 11-09-11, 02:05 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
Originally Posted by rmtdiy View Post
I feel like I can only improve the stability of the GFCI circuit by permanently disconnecting the "extra" ground
All grounds must always be connected; it was correct as it was. The ground being connected or not will have no bearing on the stability or function of the GFCI device, which at 16 years old is plausible that it just needs to be replaced.
 
  #3  
Old 11-09-11, 02:50 PM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 6
Thanks for your reply to my "situation", Ben. I expected the "extra" ground would potentially allow voltage fluctuations outside of the smaller and "closed" GFCI circuit to influence the GFCI protection in this circuit or provide an alternate path for "leakage." Anyway, that was my reasoning. It's easily put back into the "correct" state.

Relative to my GFCI tripping problem, though, I wish it was as easy as a new unit. I had already replaced the GFCI with a new unit -- no improvement. Removed all plugged-in downstream loads -- still tripping. Replaced outlets -- still tripping. Disconnected the "extra" ground, and so far so good even with loads replaced. Still doesn't make sense to me that this was the cause, as it's been that way for 16 years.
 
  #4  
Old 11-09-11, 02:56 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
Is the tripping coincident with any particular activity, using an appliance, watching TV, etc?
 
  #5  
Old 11-09-11, 03:12 PM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 6
Originally Posted by ibpooks View Post
Is the tripping coincident with any particular activity, using an appliance, watching TV, etc?
I haven't been able to isolate any activity or loads unique to the GFCI tripping. I had initially been using an induction-type charger for a tablet on the old GFCI, which seemed to trip occasionally if I also plugged in a cell phone charger into the GFCI at the same time. When this began to happen more frequently, I concluded a new GFCI was in order. Since that time, stability has been even worse with the new GFCI (tripping without any loads) until I disconnected the "extra" ground.

Assuming continued stability, I'll reattach the "extra" ground at some point and see what happens then ...
 
  #6  
Old 11-09-11, 03:47 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
This is strange behavior indeed. The ground is not connect to the GFCI mechanism at all, so it really shouldn't have an effect. In fact, GFCI works perfectly well on circuits which do not have a ground at all.

The only thing that comes to mind is perhaps the ground (maybe a ground loop) of the two sections of the circuit is picking up RF interference like an antenna and causing a false trip in the GFCI. Modern GFCIs are quite well shielded from RF so replacement should have fixed it if this was the problem.

Is there any chance the cable is damaged or kinked and moving the wires around during the act of swapping out the ground wires accidentally fixed an intermittent short? Any chance the wiring is damaged inside the walls by recent picture hanging, siding, rodents?
 
  #7  
Old 11-09-11, 04:49 PM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 6
Aside from the fields from the induction charger, I can't think of any recent changes that would have created RFI. Everything continues to function fine now as previously configured, except that the "extra" ground has yet to be reconnected.

Relative to wire condition, it's kind of difficult to get a good handle on this, as the interior of the boxes and wires have overspray from when the walls were finished. I'm referring to the spray that is applied and knocked-down to create an orange-peel-like texture (not sure of the proper term) and minimize taping efforts. No recent changes in this area to create damage or, for that matter, rodents. The location of the outlets is just above counter level in the kitchen, with the first downstream outlet only four feet away (above the sink) and the second (last) outlet only another foot-and-a-half further away. The cabling and terminations were unchanged until I began the process of chasing down the cause of the GFCI tripping.

Probably unrelated, but I just remembered that I did have some warranty service work done on our duel-fuel range a couple of weeks back. The manufacturer had introduced an "enhancement" to reduce audible noise from the fan that cools the range top electronics when the oven is on. I think this enhancement was essentially a ceramic-enclosed resistor to reduce fan rpms. The range is on the opposite side of the kitchen and has its own dedicated high-voltage circuit. Tripping of the GFCI has been happening with the oven not in use.

I did notice that the last downstream outlet plate had a light smoke-like film behind an adaptor plug for phone base unit / answering machine. If the wall plate wasn't white, I wouldn't have noticed it all. It took a bit of work to wipe it off. I have a vague recollection of seeing this before. Not sure exactly what to attribute this to. The temperature of this outlet seems to be in keeping with all others in the kitchen. Measured them with an infrared thermometer and they all measure in the low 70F range. Nothing feels warm to the touch. Never any smell of hot electronics. I'll reconnect the ground now and try to focus on any abnormalities in this outlet box.


Originally Posted by ibpooks View Post
This is strange behavior indeed. The ground is not connect to the GFCI mechanism at all, so it really shouldn't have an effect. In fact, GFCI works perfectly well on circuits which do not have a ground at all.

The only thing that comes to mind is perhaps the ground (maybe a ground loop) of the two sections of the circuit is picking up RF interference like an antenna and causing a false trip in the GFCI. Modern GFCIs are quite well shielded from RF so replacement should have fixed it if this was the problem.

Is there any chance the cable is damaged or kinked and moving the wires around during the act of swapping out the ground wires accidentally fixed an intermittent short? Any chance the wiring is damaged inside the walls by recent picture hanging, siding, rodents?
 
  #8  
Old 11-09-11, 05:23 PM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 6
Originally Posted by rmtdiy View Post
... I did notice that the last downstream outlet plate had a light smoke-like film behind an adaptor plug for phone base unit / answering machine. If the wall plate wasn't white, I wouldn't have noticed it all. It took a bit of work to wipe it off. I have a vague recollection of seeing this before. Not sure exactly what to attribute this to. The temperature of this outlet seems to be in keeping with all others in the kitchen. Measured them with an infrared thermometer and they all measure in the low 70F range. Nothing feels warm to the touch. Never any smell of hot electronics. I'll reconnect the ground now and try to focus on any abnormalities in this outlet box.
I should also have noted that the smoke-like film was limited to the outer surface of the wall plate in the area covered by (under) the adapter plug for the phone base. So this film was not on the inside of the outlet box or the back side of the outlet plate.
 
  #9  
Old 11-09-11, 07:39 PM
Member
Join Date: Oct 2008
Posts: 1,312
GFCI's are like "bank tellers". Only the hot and neutral wires are monitored. The "bank teller" counts the amount of electricity going out the hot. Then checks to be sure the *same* amount of electricity returns on the neutral.

If "one cent" of electricity is missing, then the teller "sounds the alarm" as there has been a theft of electricity! The guards instantly turn off the power.

Of course not the exact way things work, but that is the general idea. "Missing electricity" would be going to a ground connection or some other way to ground like through a person's body.

So things which would trip a GFCI, would be "leaking" electricity, to ground.

Note that surge protection devices, such as are common with computer equipment, out and out "short" the hot and neutral connections to ground in the event of a voltage surge. A voltage surge can be very brief in time and you would not even notice it. Surge protectors will trip a GFCI when there is a voltage surge.

Some devices with a "polarized 2 prong plug" may use the neutral as an internal ground. They should not do that, but from China anything is possible.

And dirty greasy electric motors can "leak" to ground.

You can test for leaks to ground with an ohm meter on its highest setting. And if you were being "shocked" by say a handheld hair blow dryer, you would not notice it. All you would notice is the GFCI tripping. Then think the GFCI is the problem when in fact the hair dryer is the problem.

A GFCI...

 
  #10  
Old 11-10-11, 09:32 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
Originally Posted by rmtdiy View Post
I'll reconnect the ground now and try to focus on any abnormalities in this outlet box.
It would at least be worth opening the box to check for loose connections. The "film" is probably just the usual crud in kitchen air but I suppose it could be from an shorting wire in that box although that problem is usually more obvious in sight and smell.

Another test on a whim would be to check the voltage with a multimeter set on the AC scale between blades hot and neutral, neutral and ground, and ground and hot. Values should be appx:

hot-neutral: 120V +/- 5%
neutral-ground: 0-2V
ground-hot: 120V +/- 5%

Test both with no loads on the circuit and with a significant load on the circuit like a hairdrier or toaster.
 
  #11  
Old 11-10-11, 05:31 PM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 6
Thanks for your input, ibpooks and bill190. The problem seems to have been resolved (at least so far). I purchased another new replacement GFCI this morning and swapped it out for the previous new replacement unit. Five hours later there hasn't been a single ground fault detected. The new unit is the same model, so I've concluded that the first unit is defective.

Sometimes the easiest solutions are the easiest to overlook. So much for my faith in quality manufacturing.
 
  #12  
Old 11-11-11, 12:10 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
Originally Posted by rmtdiy View Post
so I've concluded that the first unit is defective.
That certainly could be the case. I think another reasonable possibility is that the act of changing the receptacle might have rearranged the wires to stop an intermittent short or kink. Sometimes a bare ground wire contacts a device screw or something like that when you repack the box.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes