I have had this happen twice if about three years, here’s the story…..

I had a room with several outlets on the circuit. The wiring is 12-2 with a ground. The outlets are rated at 15 amps; the circuit breaker is 20 amps. (It is my understanding that multiple 15 amps outlets on a 20 amp circuit are okay??)

The first time it happened the computers and other devices would kick off and then go back on, I was checking the outlets that had stuff plugged into them but couldn’t find anything. Then after awhile I happened to notice smoke coming from an outlet that didn’t have anything plugged into it. The outlet was melted. I assumed it was a bad outlet and replaced it. No more problems in that room.

The other morning I was on the computer (moved to a different room) and heard a sound like plastic rustling. I looked around and couldn’t find anything. Then I saw smoke coming out of an outlet. There were a couple of computers and lights on the circuit, but the only thing plugged into this outlet was a TV that was not turned on. Also on this circuit was a space heater. But it was not plugged into the outlet that was smoking. A heater may have been plugged into the circuit in the first instance of this happening; but I’m not sure. But in neither case did a breaker ever trip.

So then I’m paranoid and ready to replace all the outlets with 20 amp outlets and install all AFCI breakers.

My brother-in-law talked to an electrician friend of his and he said that multiple 15 amp outlets on a 20 amp circuit is okay. He didn’t recommend replacing all my breakers with AFCI breakers; he said they would be tripping all the time. He seems to think that I almost had to have a bad or loose connection in the outlet box and the amp surging of the space heater caused it to start arcing and melt the outlet. He said the amp draw jumps pretty high on space heaters but doesn’t hold long enough to trip the breaker.

So what do you guys think? Do I need to physically check the connections in every box in my house? Is there any kind of device other than the plug in circuit testers that can check them? (The first time this happened the plug in tester that checks wiring status showed the outlet as good just before it started smoking.) Do you agree that AFCI breakers on everything are a bad idea?

 

Just curious, how did the wires attach on the devices? Were the wires connected via backwiring? (sticking the wires in the holes in the back versus the screw terminals) If so, these connections are prone to failure and I would go around and check every outlet and switch, and make sure the screw terminals were used.
Correct by NEC rules.
I agree. But a loose connection doesn't need to be arcing in order to get hot and cause damage. All it takes is to be loose.

Just some ideas...

 

No, they were screwed to the sides. The wiring passed through the box, line in on one set of screws and line out on the other set of screws. They were attached properly as far as I could tell and were properly grounded. But the outlet was damage so severely I couldn’t tell if anything had been loose.

 

Backstabs are normally the cause of this but not in this case. It was a loose connection. The question is why did it come loose.
What type of wire do you have? Aluminum wire is a possible cause. Or it could be the original electrician just didn't tighten the screws enough.

 

12 gage wire will generally NOT fit into back stab connectors.

You need to check for loose connections. That means opening each and every junction box (regardless if it for a receptacle or switch or just a box) and remake the connections.

You also have to lose the space heater. They are more problems than they are worth.

 

I have seen space heaters burn wires in J-boxes other then where they were plugged in. My guess would be the melted receptacle feeds the receptacle that the heater is plugged into. A poor connection at the melted outlet caused heat, heat deteriorated the receptacle, as the receptacle got worse the heat increased till finally the receptacle melted. When I worked apartment maintenance saw several receptacles killed by space heaters.