Funny how things work out sometimes. Today I had an emergency job at a dentist office that I had wired on two years ago. We had done the addition which had a couple of patient rooms, the dentist's office, lab, sterilization room and lots of x-ray equipment ( if you've never done one, try it, it's gobs of fun). But the old existing building had been wired in greenfield. So I get a frantic call from their office yesterday that the lights are out and the breaker shoots fire when you try to reset it. To make a long story short the insulation on one of the lighting circuits had deteriorated and was arcing out. We told them to shut down and we would gut the old greefield and solve the problem. So today thats exactly what we did.
Now I had one of my helpers open up a switch box to see if it was fed from old or new wiring. He said well there's only one new BX in the box and it's tagged red on the white wire. He didn't get it being a newbie, but when I explained the rule it hit him. "OK, so when you change a white to a hot you've got to mark it so you don't get bit"... I said "that's right"!
