Receptacle meltdown. No overload, no short - bad contact? Bad receptacle?

Status
Not open for further replies.
S

SparkyNH

Member
Location
NH
Occupation
GC
Owner of a home my company built calls my office saying his EV charger isn't working properly and the company told him it was house wiring related. I stop by to take a look, sure enough the thing is hot to the touch. I shut off the breaker and open up the box, and find... this. First thing I do is call my electrical sub.

NEMA 6-50 receptacle, #8 THHN, load is a 32A EV charger (bc of continuous use everything derated to 80%). Inspected and passed.

Close look at the box and receptacle shows insulation was intact, no short (4th picture with extra insulation stripped was afterwards; I cut back the burned insulation).

My sub insists he did everything right... What could have caused this? Faulty receptacle? Poor contact? (The screw *was* tight.)

Sub replaced the receptacle so homeowner is happy, but I need to know what caused this in the first place.

https://imgur.com/a/imGWavy
 
Or threads on lug were damaged, cross threaded, etc. and even though enough torque may have been applied it didn't tighten down enough on the conductor. Regardless sure looks like not good enough connection between conductor and lug.
 
Thank you, gentlemen.
The only thing I could think was bad contact... either between the wire and the lug, or between the lug and the blade contact, or between the blade contact and the blade.

(I can say though that the lug screw was quite tight... I unscrewed it myself and it was quite tight, and didn't seem like it was crossthreaded, etc.)

I guess I'll chalk this up to random chance (maybe a faulty receptacle or something), and not give the sub too much of a hard time. :)
 
kwired said:
Or threads on lug were damaged, cross threaded, etc. and even though enough torque may have been applied it didn't tighten down enough on the conductor. Regardless sure looks like not good enough connection between conductor and lug.
Click to expand...
I would guess that too. I’ve seen lots of poor quality devices, in spite of UL labels.
 
The resistance R of a bad connection causes very localized heating under load, at the point where the R is. Bad connection would have been either at the plug blades connection or the wire termination. If it started at the plug connection, the male plug blades would look worse than the wire termination. If the male plug blades look good, the localized heating started at the wire termination and travelled out from there.

Seen some stuff that was never tightened. More common on state and town jobs.
 
Screw was tight is meaningless after the meltdown. Thread will tighten (or seize) after heating up like that, and appear tight. I've had to pull a main out at a service call once that if all you did was put a driver on it the tried to turn it would seem tight but the wire actually just about fell out of the connector (pulled out with no effort). Don't know the installer but could have been crossed threaded never could find out for sure as the lug end inside you could see was actually welded together.
 
Status
Not open for further replies.
Top