RAY: This puzzler is from Gary from Santa Clara, who writes:
As a shade tree mechanic, I've read many times that when removing a car's battery or doing electrical work, one is supposed to disconnect the negative terminal first, and only then the positive terminal. Installation, as so many instructions say, is the reverse of that procedure.
As an electrical engineer, I scoffed at these instructions. I knew that opening a circuit at any point was equivalent to opening it anywhere else. I just disconnected whatever terminal was handy.
One day, I was helping a friend change the battery in his garden tractor. He happened to be an electrician, and he knew as well as I did that it didn't matter which terminal was removed first.
But, as we learned the hard way that day, this isn't true. It does matter which is removed and replaced first.
Why is that?
__________________
The Principle of Least Interest: He who cares least about a relationship, controls it.
RAY: This came from a fellow named Josh Kokendolfer, who says it's a true story.
It was a brisk December morning. A co-worker and I had a simple job to do that day: clean out a job site and take the trash to the local landfill. And we had an F-350 pickup that was outfitted with a dump-truck bed. We filled it up and headed out. When we arrived at the landfill we pulled the truck onto the scale that weighed our vehicle and the woman in the office waved us through.
We unloaded and headed back out to the scale. Once again our truck was weighed. Before getting into the truck I noticed that one of the back tires was low. I decided to stop at one of the local gas stations to check it out and fill all the tires just in case.
After lunch we loaded the truck a second time at the site and headed back to the landfill. Everything went just like the first time. After we were weighed on exiting, I went to pay the bill. My co-worker looked at the paperwork and noticed something strange.
The first time we left we weighed 6,480 lbs. And the second time we exited we weighed 6,440 lbs - a difference of 40 lbs. We were being charged for an extra 40 pounds of trash that we didn't have. I immediately complained to the office manager. She said, "There's nothing wrong with our scales." Well, if that's the case, what happened?
The 40-Pound Difference
RAY: The reason the truck weighed 40 pounds less is that it had burned 40 pounds of gas, or about six gallons.
__________________
The Principle of Least Interest: He who cares least about a relationship, controls it.
I figure if I'm careless and allow the socket wrench (or any tool) to touch both the cable clamp and any body part at the same time, while the clamp is still attached to the battery terminal,
it doesn't matter. The cable is already grounded to the battery.
BUT if I'm working on the positive (red) terminal clamp first, and accidentally touch both the cable clamp and any metal body part ...
ZZAPPP !!!!!
__________________
The Principle of Least Interest: He who cares least about a relationship, controls it.
