I saw a short piece on the news about a homeowner that was electrocuted just days after moving into his new house. It happened near me in Clermont, Florida. They didn't give much information on the news, but they did show part of a video taken by the HO's wife's lawyer. Apparently the guy was killed when he was connecting the clothes dryer vent hose onto the metal duct. The duct had voltage on it. The video showed an electrician reading 120vac on the metal part of the bathroom medicine cabinet. He checked the cabinet and used the ground on the nearby receptacle. The investigation found a drywall screw through a metal wall stud and into an unsupported piece of nm inside the wall. They said it was only into the ungrounded conductor in the romex. Supposedly the metal studs were energized, and I'm guessing that the dryer duct was secured to the studs. You would think the breaker would have tripped, unless they had poorly installed grounding, also.
Edited for spelling
[This message has been edited by XtheEdgeX (edited 02-22-2006).]
Edge, this is not unusual. There is no metal in the wiring method, box or even the plumbing. I am not sure where the path would be to trip the O/C device until the dryer does get hooked up. These houses are built on a slab with an isolation membrane under the steel framing. The panel will be on a block wall in the garage. Everything is in Romex with plastic boxes. If they don't get caught with a luminaire having to go directly over a stud, requiring a pancake box I am not sure there is any way the steel gets bonded. In commercial with EMT and steel boxes this is not a problem. It gets bonded all over the place. I bet we start seeing metal framing coming under 250.104(C) The contractors probably could have made this issue go away if they just used steel boxes for the dryer and the range. That would give them some fat EGCs bonded to the steel with a few pennies added to their cost. If we get required bonding under 250.104(C) they will be stringing #4 or larger all over.
We had similar problem in the housing industry a few years back. One of the home builders was using a sheeting on the outside of the house that had a thin layer of material that looked like aluminum foil. Some type of thermo barrier. Then the vinyl siding was nailed on top. The siding guys were using 1 1/2" and sometimes 2" nails and the nail would penetrate the romex and electrify the skin of the sheeting, the down spouts and I had 88 volts to ground on one of the brick fronts of a house. The guy doing the pressure washing kept complaining that he was getting shocked and was smart enough or lucky enough to get away from the house. As a result I haven't seen any of this type of sheeting being used since.
The siding guys were using 1 1/2" and sometimes 2" nails....
Has anyone else noticied the tendency of people to use the biggest nail they can find, regardless of the job? If they're attaching to 3/4 plywood, what do they really think that extra 1.25" of nail is actually doing? I recently had a nail-through-the-Romex repair because the H/O was using 10d finish nails to attach quarter-round molding to his baseboard. That must've been load-bearing baseboard-trim...
I had one where the cabinets were hung with 4" drywall screws and they got the romex right in the middle. Never told the homeowner about the sparks. I found it by opening the cabinets and seeing the burn marks. Rod
A little bit off topic, but I never leave a kitchen rough in without using nail plates over every cable filled hole in the walls that will be behind either the upper or lower cabinets, regardless of how well centered my holes were in the studs. I have seen those 4" long screws in the finish carpenter's parachute bags one too many times.