Customer: "When I unplugged my clothes dryer to move it the plug sparked and all my lights went out"
Finding: The "service" was some surface mount porcelain fuse holders on the porch (yes, outdoors but with a roof over it). The neutral was fused and that fuse was blown.
The dryer had (like they all used to) its neutral bonded directly to the frame of the machine. Some well-intentioned person had attached a ground wire from the frame of the dryer to the cold water pipe feeding the adjacent washer.
This gave the electrical system a path to ground as long as the dryer was plugged in.
Of course, when we first got there my boss (I was a helper at the time) was sure they had to be wrong and was he ever surprised when he pulled the 30 Amp plug out and it drew an arc and the lights went out!
They had a new 100 Amp service within a week.
