Last year sometime, I consulted for a designer on a project with a magnitude of problems. One such problem, the last straw that broke the camels back for the designer, was an accusation that the cabinet installer had drilled a screw into a wire into the wall and shorted out the entire upper floor. The client was without electricity. At the time, I responded verbally that there were one of three things that could possibly have happened, and this is the first time I've been able to take a minute and snap a view examples to illustrate:
1) The wrong screws
The installer used 4-inch screws to mount the wall/tall cabinets into the wall thereby penetrating the stud and the 120V Romex cable in the wall. This is what a typical cable run looks like behind the wall:
What you are seeing here is a vertical stud with a 120V Romex cable running through a hole bored through the stud. There is just over 1-inch from the edge of the stud to the hole. Not only is it imperative for strength that the stud be bored in the middle, but you can see that there are also old drywall nails sticking out, staples, what have you - and this is just the beginning of what happens to the stud.
Remember that a stud is 3 1/2-inches x 1 1/2-inches, then adding drywall adds 1/2-inch each side making the total wall thickness 4 1/2-inches (or finished dimension) and adding a cabinet onto the wall would be an extra 3/4-inch of material to go through. If the electrical cable is in the middle (as is shown in the figure above) making 3-inches from the cabinet back to the middle of the stud, then a 4-inch screw would likely penetrate that electrical cable - and the installer would likely not have a drill that works, or possibility worse, a fire would start. In our example, the client's house still stands and the drill still works, and the installer used 2 1/2-inch screws, so what would be the other possible cause?
2) Blocking plates missing
Whenever that bored hole, where the cable runs through, is less than 1-inch, or is notched into the stud, a small blocking plate shall be installed to prevent any penetration of the electrical cable. This is what a blocking plate looks like when installed correctly:
As you can see, the plates are 1 1/2-inches wide and are simply tacked into place. The drywall goes over-top and no one is the wiser that you house is safe and sound from any long screw (or other blunt object) from penetrating the cable.
3) Inspection did not pass/was not permitted
These little blocking plates are literally pennies each and there is no excuse for their absence. Any municipal inspector would spot their absence during electrical inspection. In our client example, I would venture to gain that the electrical was not properly inspected. It is always vital that you obtain a proper permit for all work on your home because your insurance may not cover you in the event of a loss.
On this particular day that I took these photographs, it was electrical inspection day. It is my duty as the designer to sneak in before inspections to make sure that everything is going to work out according to the plan. We're all human, we all make innocent mistakes, and catching them before that drywall goes up and inspection is passed puts us all that much further ahead of the game.
Thank you to the designer for providing a real-life example. Thank you to the electrician for allowing me to document. Both wanted to remain nameless, but they are both inspiring and excellent at their respective jobs. Do more good work!