BlueRidgeMark
Addicted to ArboristSite
I'm guessing that you folks have been taught that "insulation" means something that will prevent electrocution.
That's not what the term means. Insulation is simply something that impedes the flow of electrical current. It's not an absolute. Some insulators are better than others. Vacuum is insulation. (Check what's inside an electronic tube. Er, "valve" for the Brits.) A plastic sandwich bag is insulation. Even pure water is insulation. Add some salts to it and it becomes a very good conductor. NOT an insulator!
Even air is insulation, if you have enough of it. That's why the ceramic insulators on power lines are corrugated. The corrugations make for a longer path for electricity to travel, thus improving the insulating properties.
Air is what USED to insulate house wiring, back in the old days. That and a little cotton. Yes, cotton. House wiring was originally wound with cotton thread, and the wires were run on the walls, exposed, with the two phases separated by about two inches. The cotton and air were enough INSULATION to prevent the current from flowing between the wires.
Wasn't very safe, though. That's why it was moved inside the walls. The cotton and air weren't good enough insulators for safety.
No insulator is perfect. Most lose some insulating ability when heated. All will break down when presented with enough voltage. Many inulators break down gradually, some break down catastrophically, that is, suddenly. All can be physically breached (as with the often mentioned pinholes).
If there were no insulator between the wires on a house drop, the current would flow directly from one wire to another, much faster than the transformer could handle, and it would overheat and explode.
Oh, Boston, take a look at the second row, on the right end.
http://www.fujikura.com/prod/power/p10_3.html
Or take a look at this:
http://tinyurl.com/28lf3r (Fair warning - it's a PDF file.)
Here, I'll quote it for you:
Here's a similar listing ('nugher PDF):
http://tinyurl.com/2gejg9
Hmmm. The insulation on this brand can be ordered in 45 or 60 mill thickness. Cool.
Uh, yes, that IS aerial drop.
Guys, I know what happens in these industrial classes. The material is not intended for engineers, the purpose is SAFETY. So the material is often written by professional writers, who are NOT technically competent in the material they are creating. They are given the raw information, and they convert it into a curriculum. Important distinctions are often lost in the translation. Then some guy gets sent to a class, where he's expected to learn the material and then become a trainer himself. More gets lost in the translation.
So you guys who take the classes often get wrong information. That's how it works.
So, Boston, what's for lunch?
Did you take that crack as an insult? If so, I most sincerely apologize. I did NOT intend to insult you. I was just making a joke. A bad one, perhaps, but I certainly was NOT trying to insult you.
