Ground fault between disconnect and panel?

Reply

  #1  
Old 05-15-19, 11:02 AM
Member
Thread Starter
Join Date: May 2006
Location: Dallas, TX USA
Posts: 35
Ground fault between disconnect and panel?

I think I have this figured out, but curious if anyone can either validate my thinking or tell me where my assumptions are wrong.

- 200 amp disconnect next to the meter
- aluminum feeder from disconnect to the main panel about 25 feet away inside the garage
- neutral and and ground are bonded in the disconnect, but separate in the main panel inside the garage

I am attempting to install a few AFCI breakers, but they trip immediately. Normally I would think it was an issue in the circuits I was attaching the breakers to, but I am having the same result regardless of which circuit. As a result, I wired a temporary circuit directly from the panel, with nothing except a single receptacle on it. Same result. I have also tried multiple AFCI breakers, from multiple different sources, and all the exact same result.

With all power turned off at the disconnect and nothing connected in the main panel (literally no hot, neutral or ground wires connected), except the feeder from the disconnect, I measured the impedance between Ground and Neutral. It showed 0 (no resistance at all). Shouldnít I at least see some impedance from the 50í of aluminum between the panel and the disconnect and back?

So, my thinking is that there is some sort of ground fault between my main panel and the disconnect. Before I replace the aluminum feeder from the disconnect, I just want to make sure I havenít missed anything.

Any thoughts would be much appreciated
 
Sponsored Links
  #2  
Old 05-15-19, 11:08 AM
Member
Join Date: Jun 2012
Location: USA
Posts: 1,320
Do the breakers trip if nothing wired to them?

Sounds like you may not be connecting the circuit neutrals to the breakers.
 
  #3  
Old 05-15-19, 11:17 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,779
Likes Received: 8
You should get a very low resistance reading between neutral and ground at the main panel due to the bond in the service disconnect panel. It's not surprising this would read zero ohms over 50 feet as the expected resistance for #4/0 aluminum is 0.25 ohms per kilometer; this would be out of the expected accuracy range of most meters.

Whatever this problem is, it is not related to the upstream feeder as a ground-neutral bond on the supply side of an AFCI or GFCI breaker has no effect on its operation. Install an AFCI breaker in the panel with only the neutral pigtail installed -- no hot or neutral wires connected to the load terminals. If you can turn the breaker on, it is functioning normally. If after your hot and neutral are connected the AFCI breaker trips, then you have a problem with the branch circuit wiring.
 
  #4  
Old 05-15-19, 11:27 AM
Member
Thread Starter
Join Date: May 2006
Location: Dallas, TX USA
Posts: 35
Got it. So not worth worrying about the feeder then.

I will try to attach the breaker with nothing attached to see what happens. These are Square D QO breakers for plug on neutral, so there is no pigtail.

Can the quality of the ground affect this? I donít have good knowledge of what the grounding source is for this house (built in TX in early 80s)
 
  #5  
Old 05-15-19, 11:35 AM
Member
Thread Starter
Join Date: May 2006
Location: Dallas, TX USA
Posts: 35
Ok, so I can confirm that if I attach the breaker (plug on neutral type) to the panel, it does not trip. If I push the test button, it trips the way it should. So, it seems then that this is an issue with the branch circuits for sure. Agree?

Is it normal that a house from the 80s would literally not have a single circuit that would work with AFCI? It seems there would have to be some pretty serious shared neutral craziness to make that happen. The wiring itself seems in good shape, so I would assume itís an issue at the different end-points.
 
  #6  
Old 05-15-19, 11:41 AM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 6,110
Likes Received: 2
Agree. Just to verify, are you attaching the branch circuit neutral to the breaker?
 
  #7  
Old 05-15-19, 11:44 AM
Member
Thread Starter
Join Date: May 2006
Location: Dallas, TX USA
Posts: 35
Well, itís a plug on neutral panel and iím using the plug on neutral breakers, so as soon as I attach the breaker it is connected to neutral for the purpose of the AFCI. The only thing not connected at that point, is the load right?
 
  #8  
Old 05-15-19, 12:52 PM
Member
Join Date: Apr 2019
Location: USA
Posts: 100
Likes Received: 11
As Astuff and Joed mentioned, are you connecting the neutral wire from each branch circuit to the load neutral output terminal at the bottom on the side of the AFCI breaker (i.e., below the breaker's hot output terminal)?
The plug-on neutral eliminates the need for the line side neutral pigtail, but you still need to land the branch circuit neutral on the breaker.
 

Last edited by engr3000; 05-15-19 at 01:14 PM.
  #9  
Old 05-15-19, 12:52 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,779
Likes Received: 8
Right, the breaker is connect to both hot and neutral bus bars via the plug-on. The branch circuit hot and neutral wires should then get connected to the screw terminals on the side of the breaker.

If there are shared neutrals between circuits or neutrals bonded to ground (bootleg grounds) out in the branch circuit wiring the AFCI breaker will either not reset or will trip immediately.
 
  #10  
Old 05-16-19, 06:32 PM
Member
Thread Starter
Join Date: May 2006
Location: Dallas, TX USA
Posts: 35
Well, that is just embarrassing. I completely misread the printed instructions with the QO breakers. In my defense, I think the instructions are super awkwardly written. The instructions on the Square D website are much clearer: https://www.schneider-electric.us/en/faqs/FA274612/

With the branch circuit neutral wired directly to the breaker as opposed to the neutral bar (which obviously makes complete sense anyway), this works exactly as it should.

Thank you for the help. Iím glad I asked before I wasted more time on this! 👍
 
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