In the 80's--early 90's I worked in HVAC, mostly service. But I helped with some installs and retrofit, and did the AC end and startup/ checkout. Showed up at a farm house the guys were rattling back and forth through an old closet entrance into an attic area, and one of them came out and bumped right up against some BARE (some of it was installed that way) knob and tube. I did a quick check with a meter an yup!!! LIVE. So I stopped the crew right there and gave them a "little education."
The look on their faces? PRICELESS. guy wonders what they had been doing earlier!!
