Reversed polarity in outlet prevents GFCI from working?

Reply

  #1  
Old 12-11-07, 09:07 AM
Member
Thread Starter
Join Date: May 2003
Location: Suburb of Detroit
Posts: 283
Received 0 Votes on 0 Posts
Reversed polarity in outlet prevents GFCI from working?

Quick question because I'm curious.

I recently moved into an 8-year-old house and have been trying to identify electrical problems and fixing them. One I found the other day: the previous guy ran a new circuit to power three outdoor receptacles in the front of the house (for christmas lights). The first receptacle is a GFCI that protects everything downstream. Next come receptacles A and B in a double-gang box, followed by receptacle C in a single-gang.

C worked fine and tripped the GFCI when I used my little tester on it (three-prong push in tester with little button to trip GFCI on the top).

A and B were wired with the hot and neutrals reversed. I could not trip the GFCI on either receptacle. Yesterday, I fixed the wiring problem and now the GFCI trips properly when using my tester on both A and B.

So, my question--is this normal? I see three possibilities:
1. An improperly wired downstream receptacle is unprotected in this instance.
2. My tester can't trip the GFCI if the receptacles are miswired.
3. Something is wrong with the GFCI and it should be replaced.

My guess is "1" but I wanted to know for sure. Thanks!
 
Sponsored Links
  #2  
Old 12-11-07, 09:19 AM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
Even with reversed polarity, you should still be able to trip it with the internal tester (the "test" button on the face of the receptacle). But not with the external tester.

In any case, fix the polarity.

The internal tester is reliable in all cases. The external tester is not always reliable.
 
  #3  
Old 12-11-07, 09:23 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
In the setup you provided the GFCI will trip just fine with a true current imbalance between the hot and neutral. After all, the GFCI has no way of knowing that the hot and neutral wrere reversed at a downstream receptacle.

What you ran into is that your tester (and any inexpensive tester) cannot provide a current imbalance when the hot and neutral are reversed.

The tester works by passing a small amount of current from the hot wire to the ground. The amount is not large enough to trip the circuit breaker, but is more than enough to trip a properly functioning GFCI.

However, in your case the tester actually connected the neutral wire to the ground wire. Since no current is available on the neutral, nothing flowed to the ground wire, so the GFCI did not trip.

If you want to prove this to yourself, try this experiment. Plug your tester into a three prong to two prong adapter. The plug this adapter backwards into the receptacle. In other words, make sure that the neutral prong of the adapter plugs into the hot prong of the receptacle and vice-versa.

Next connect the ground tab or wire of the adapter to the ground of the receptacle. You should
be able to do this through the screw on the center of the duplex receptacle.

Finally, press the GFCI test button on your tester. This should trip the GFCI. It will be connecting the neutral wire of the receptacle (which is hot) through the tester to the ground on the circuit.
 
  #4  
Old 12-11-07, 09:48 AM
Member
Thread Starter
Join Date: May 2003
Location: Suburb of Detroit
Posts: 283
Received 0 Votes on 0 Posts
Thanks a lot, that all makes sense.
 
  #5  
Old 12-11-07, 05:25 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 13,057
Received 73 Votes on 65 Posts
Thanks Racraft! I learned something new on that one.
 
  #6  
Old 12-11-07, 06:14 PM
Unclediezel's Avatar
Member
Join Date: Dec 2006
Location: Northeastern PA.
Posts: 2,230
Received 0 Votes on 0 Posts
Sorry wrong place.. please delete.
 
  #7  
Old 12-14-07, 07:44 PM
ampz's Avatar
Member
Join Date: Feb 2004
Location: Philadelphia
Posts: 536
Received 0 Votes on 0 Posts
It has always been my understanding that a GFCI will not interupt a fault if it is miswired. A few years ago Leviton came out with their "SMARTLOCK" line of GFCI devices that prevent a GFCI circuit from becoming operational if the GFCI {or any receptacle downstream} is miswired. The only other manufacturer that I can think of that uses this technology is Pass & Seymour
 
  #8  
Old 12-14-07, 08:02 PM
Member
Thread Starter
Join Date: May 2003
Location: Suburb of Detroit
Posts: 283
Received 0 Votes on 0 Posts
Originally Posted by ampz View Post
It has always been my understanding that a GFCI will not interupt a fault if it is miswired. A few years ago Leviton came out with their "SMARTLOCK" line of GFCI devices that prevent a GFCI circuit from becoming operational if the GFCI {or any receptacle downstream} is miswired. The only other manufacturer that I can think of that uses this technology is Pass & Seymour
It wasn't the GFCI that was miswired. It was two of the downstream protected receptacles that had their hot and neutral reversed.
 
  #9  
Old 12-14-07, 08:18 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
A GFCI has no way of knowing if something downstream is wired backwards. New ones can and do detect the LINE terminals, but they just cannot detect anything downstream wired backwards.
 
  #10  
Old 12-17-07, 02:24 PM
Banned. Rule And/Or Policy Violation
Join Date: Dec 2007
Location: Chicago
Posts: 1,011
Received 0 Votes on 0 Posts
Originally Posted by ampz View Post
It has always been my understanding that a GFCI will not interrupt a fault if it is miswired. A few years ago Leviton came out with their "SMARTLOCK" line of GFCI devices that prevent a GFCI circuit from becoming operational if the GFCI {or any receptacle downstream} is miswired. The only other manufacturer that I can think of that uses this technology is Pass & Seymour
All GFCI's manufactured since July 2006 trip and will not reset power "to the receptacle face" if there is a line-load miswire, see for example.

http://www.iaei.org/subscriber/magazine/06_c/esfi.html

I do not know if any type of GFCI they can detect line-load reversal in downstream devices, perhaps someone else here does.
 
  #11  
Old 12-17-07, 03:33 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
[quote=Michael I do not know if any type of GFCI they can detect line-load reversal in downstream devices, perhaps someone else here does.[/quote]


did you not read my previous post?

A GFCI has no way of knowing if something downstream is wired backwards. New ones can and do detect the LINE terminals, but they just cannot detect anything downstream wired backwards.
 
  #12  
Old 12-17-07, 03:36 PM
Member
Join Date: Nov 2007
Posts: 160
Received 0 Votes on 0 Posts
the new gfci will not let you connect the line voltage side to the load side of the device meaning "backfeed" the GFCI (work unprotected)

As far as the GFCI knowing if the downstream recepticles are wired correctly (reverse polarity) the answer is no
 
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
 
Ask a Question
Question Title:
Description:
Your question will be posted in: