Re: Ground Rod causes Fire
A couple of years ago, a fire insurance investigator asked for advice about a house fire he was working on.
It was discovered that the service grounding electrode conductor had become disconnected (or burned off) at the first ground rod, just below and a bit to one side of the meter location. It wasn?t fastened and was dangling in the wind.
At every point where it had touched the concrete foundation a spall of concrete was blown off, and at every point where it had touched the wood steps there was a burnt area, and at one point had set the steps afire.
The earth was dried out (baked, he called it) surrounding the ground rod. A fire started at the oil-fired water heater, which was connected to the outdoor (grounded) oil tank by a 3/8 inch copper tubing oil line.
This is what I think happened.
I believe that a winding-to-winding fault developed in the Power Co. transformer. Because the secondary neutral is normally tied to the grounded primary neutral, that should blow the high-voltage fuse in the primary cutout.
If the ground tie between the primary and secondary neutrals on the pole was open/broken/missing, the fault current would try to return to the primary neutral through the service grounding conductors, through the earth to another pole, and up the "butt-plate" ground wire to the primary neutral.
The service ground wire at the house burned off (or was previously disconnected) at the first ground rod. The fault current then tried to get to ground through the oil line to the grounded outdoor oil tank, burned off the 3/8 inch copper oil line and ignited the oil.
Any thoughts on this one?
Ed
