Wow....Needed to Replace GFCI for Charger

I blame the original wire and inadequate torque on the screw that was supposed to hold it. If a little loose and/or the wire not throughly cleaned, the resistance with a 12A load would easily overheat the wire and screw. Also, the loop didn't cross which again means less area, higher resistance and letting the smoke out.

If my home:

1. Use sandpaper to reduce the wire to bright metal.
2. Get the replacement GFI.
3. Make a loop and slip over the screw with the cross outside of the seat.
4. Torque down the screw with enthusiasm.

The goal is to maximize the area of the wire pressing against the screw and base.

GOOD LUCK!
Bob Wilson

 

I suspect that terminal on the old GFCI was undertightened. I wouldn't worry so much about overtightening: that can cause (generally immediately obvious) mechanical problems like the threads stripping or a chunk of the plastic flying off, but it won't cause I²R heating like that the way undertightening will.

If you're especially fastidious and have an inch-pound torque driver, most receptacle makers will list a torque, if not right on the box, then in a data sheet from their web site. Heavier stuff like the junctions inside your breaker panel will always have a specified torque.

But generally for a common receptacle, you're ok if you find the "as secure as I can get without bending or stripping the terminal or cracking the housing" sweet spot.

By the way, from the front, that looks like a 15-amp rated GFCI (a 20-rated will have a slight T shape to one of the slots). Did you have the charger and fridge plugged into the same receptacle, or just two different ones on the same circuit?

There are two sorts of backwire arrangements you can find on receptacles. On the very cheapest kind, you just find a hole on the back, and you poke the wire in, and a sharp-edged spring grabs it, and that's all the connection you've got. Those are evil. I don't use them; if I find them I replace them. Better ones are less than a buck more.

But that's not what you're seeing on that GFCI. If you look closely, the holes on the back are just wire guides into position under the metal full-contact plate clamped down by the screw. That's a very good arrangement. It is fast to wire, electrically secure, and you're even less likely to mess it up than trying to fuss with the proper clockwise wrap around a terminal screw. So I don't blame the connection design. I suspect it was just undertightened.

As a homeowner, I'm usually only ever doing one at a time, taking my time and checking everything twice. I think when contractors are doing a house's initial wiring and installing fifty of the things against the clock, it's more likely one won't be quite right somewhere. Not that uncommon to find.

Thermal imagers are crazy cheap now, relatively speaking ... things like the FLIR One, attaching to your phone. Great for looking at something like your cord and receptacles while current is being drawn, to spot any extra-warm areas. The corner of your receptacle there would have stood out like neon.

-Chap

 

This is alternating current. Positive and negative change polarity 120 times every second. You might be thinking of the hot leg (120 volts to ground) and the neutral leg (zero volts to ground) which is bonded to ground in the panel. If they'd touched the breaker would have immediately tripped.

The damage was certainly caused by overheating, but the cause wasn't exactly the load you put on it. The cause was the internal construction of the receptacle where some skinny brass blades are all that contact the bare wire in the push-in connectors. Those blades had to take the current you were drawing into one blade and then the other blade put it into the other wire to continue down the rest of the circuit. The failure was exactly at this point as i'mJp describes. The GFCI receptacle I've seen are rated at 15 amps for what's plugged into them, but they are rated to pass 20 amps through the circuit to other devices. Maybe there are cheapo GFCI units that only can pass 15 amps, and even that should not have failed. (By the way, if you every have several receptacles dead on a circuit, look for the receptacle at the head of that circuit with a loose wire caused by these shoddy push-in connections. That happens with these 59 cent gizmos. You can screw the wires instead of pushing them in, or replace the receptacle.)

You will be in good shape with your new circuits.

How is the Level 2 charge station worth the cost?

 

Those aren't push-in connectors, they're wire guides under the screw clamp. Two very different types, as similar as they may look. Push-in with the spring is lousy. Guided screw clamp is top notch ...

... except when the screw's not tightened enough. But that can happen when you wrap around the screw, too.

-Chap