What caused this situation?

submitted by Joe Tedesco:

Here's another picture of a situation that is constantly questioned by many everywhere!

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

(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

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?

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.

Two wires of different gauge in 1 hole. Only one tight.

Top Pic Why double lug??? Looks like there a plenty of avaiable unused terminals.

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'.

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.

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.