I moved into an older home (built in early to mid 70's) about a year ago. I had a space heater plugged into one of the outlets in the living room, recently we noticed a burning smell and finally found it was coming from the heater, the cable plugging the heater into the wall was warm and when I unplugged it from the wall outlet one side of the outlet was blackened. I tested the outlet and discovered it and several other outlets through out the house are testing as "open ground". The effected area in my living room seems to also be tied into a couple of outlets in my kitchen (includes the disposal and over sink light).
Best I can tell when I flip the breaker off to kill the power to that line, it kills the power to the over sink light, the disposal, two outlets to either side of the kitchen sink and the two outlets in the living room.
With the power on, the two outlets in the living room test as open ground, the two outlets in the kitchen and the outlet under the sink where the disposal plugs into, all test correctly.
One outlet in the living room (which only had one pair of wires running to it) was a 2 prong outlet, I pulled the outlet out to find a ground wire that wasn't connected to anything. I replaced the outlet with a 3 prong outlet and connected the ground wire to the green screw on the outlet.
The other outlet in the living room was a 3 prong outlet, it has two pairs of wires coming into the box (with the ground wires twisted together. The hot and neutral wires were pushed into the back of the outlet and the ground wires were connected to the outlet. This was the outlet that the heater was plugged into. I replaced this outlet and connected all the wires using the screws on the side of the outlet rather than pushing them into the back of the outlet and connected the ground wire to the green screw on the outlet.
Once these two were replaced, I turn the breaker back on and tested the outlets again. They are still testing as an open ground.
Is there something else that I can test or replace, I don't understand why 3 outlets on the line test fine while two test open ground. There is a bookcase covering a section of the living room wall (along the same wall between the two open ground outlets) that I don't know if a plug is behind it or not, I'll be moving that tonight to see.
Could the switch to the over sink light be causing the problem? There is a switch that controls an outside deck light near one of the open ground outlets (I suspect it is tied into the same circuit), could that be part of the problem?