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#176922 - 04/16/08 08:56 AM What caused this situation?  
Admin  Offline

Administrator
Member
Joined: Oct 2000
Posts: 3,459
NY, USA
What caused this situation?

submitted by Joe Tedesco:

[Linked Image]


Tools for Electricians:

#176923 - 04/16/08 09:42 AM Re: What caused this situation? [Re: Admin]  
Joe Tedesco  Offline
Member
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
Here's another picture of a situation that is constantly questioned by many everywhere!

The termination's of the EGC and Grounded (Neutral) conductor.

[Linked Image]


Joe Tedesco, NEC Consultant

#176928 - 04/16/08 11:07 AM Re: What caused this situation? [Re: Joe Tedesco]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,135
Estero,Fl,usa
(ref top pic)
A loose connection and an uncleared ground fault?
It looks like the bottom conductor wasn't inserted all the way through and missed being clamped by the screw


Greg Fretwell

#176933 - 04/16/08 11:27 AM Re: What caused this situation? [Re: gfretwell]  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,213
Chesapeake, VA
The panel EGC and neutral look awfully small... And the terminal bus is rusty.

Looks also like the insulation wasn't stripped properly on that burnt wire, either- not only was it offset and the screw not properly clamping it, but might have been insulated from the screw preventing proper contact, too. Poor contact = not enough fault current to trip the breaker + excessive heating = fire.

This isn't an FPE panel, is it?


#176947 - 04/16/08 06:35 PM Re: What caused this situation? [Re: SteveFehr]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,874
Brick, NJ USA
Top pic...bad connections, two conductors under 1 screw. Result of low quality workmanship. This design of neutral/ground buss was in GE panels, and the installer had to get the conductor directly under the screw to get a decent termination. Two conductors result in deflection to the sides of the screw, resulting in a poor termination. the poor termination results in a high resistance connection, creating heat on the neutral conductor, and you have a pic of the ultimate end result. This is based on my opinion, and experience.

The second pic, IMHO is an OLD panel that has a corrosion situation. Also, it appears that the two conductors under 1 screw situation is here also.


John

#176956 - 04/16/08 10:15 PM Re: What caused this situation? [Re: HotLine1]  
WESTUPLACE  Offline
Member
Joined: Mar 2004
Posts: 251
Kingwood, TX USA
Two wires of different gauge in 1 hole. Only one tight.


#176958 - 04/16/08 11:02 PM Re: What caused this situation? [Re: WESTUPLACE]  
rhagfo  Offline
Member
Joined: Apr 2001
Posts: 43
Portland, OR. USA
Top Pic Why double lug??? Looks like there a plenty of avaiable unused terminals.


#176963 - 04/17/08 05:11 PM Re: What caused this situation? [Re: rhagfo]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,874
Brick, NJ USA
Rhagfo:
Terminating the neutral and ground conductors in one lug, or under 1 screw was a 'trade practice' in some areas. The reasoning was to keep the neutral & grd 'together' for tracing purposes. BTW, not a 'practice' that I have done, nor taught to anyone, but something the 'old-timers' passed on to the 'young guys'.



John

#176986 - 04/18/08 05:07 AM Re: What caused this situation? [Re: HotLine1]  
Elviscat  Offline
Member
Joined: Aug 2005
Posts: 214
Seattle Washington USA
I'd venture that a loose connection+neutral current on the EGC leads to a burnt/corroded connection. In times gone by it used to be common practice to put 2 neutrals under one screw, this created a definite hazard when one of the circuits is a multiwire, and the other circuit was being removed or serviced.


#176993 - 04/18/08 11:55 AM Re: What caused this situation? [Re: Elviscat]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
Current code would of course demand 1 neutral per terminal.
Manufacturers instruction state 1 conductor per terminal for Grounded circuit conductors. The bonding terminal however are allowed 2 #14 or 2 #12 copper or 2#12 or 2#10 aluminum under 1 screw. 1 wire per terminal for larger bonding conductors up to the largest wire permitted for the particular bonding terminal which is often #6. Larger bonding conductors can be accommodated by adding factory approved lugs to the bonding strips or to the enclosure.
I have always followed the 1 neutral 1 screw but until about 10 years ago it was as many bonding wires as would fit as long as we twisted them all together.



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