In the past week, I have encountered two examples of people having a misconception of Ohm's Law and how it works. The theme is the same in both instances, but I wanted to discuss the issue I saw today at work. About a month ago, a piece of lab equipment we call a "hotplate" had a switch failure. It is a "rocker" type of switch rated for 20 amps. The hotplate, which is basically a coil type heater inside a ceramic top plate designed to warm a fliud in a beaker or other container, is rated for 220 Volts at 15 Amps. When this failure occured a month ago, we replaced the switch, and lo and behold, the failure occured again. What essentially is occuring is the contact points of the switch are not making at rest position. One has to apply pressure to the switch to get the circuit to close and maintain it. Once you let up, the contacts again relax and break the circuit. I suspect that the contacts are getting dirty due to arching or too hot and warping. In the past month, we replaced the switch 4 times. Today, my coworker, a man with 30 years experience, and the apprentice we are training, a completely inexperienced young fellow, went about replacing the factory switch with a beefier 30 amp toggle switch. In passing, I mentioned that this might be a "band-aid" fix but might mask the real problem. Certainly, the 30 amp switch will probably last forever, but why were the factory switched going bad when they are rated 5 amps above the operating rating of the device? Possibly, a bad batch of switches from the factory, but that isn't likely. Now, here is where the fun begins. I mentioned to the senior fellow of our three man group that we may want to put an amp-probe on the circuit to check if there is a short somewhere, even a partial one. He flatly told me "Nah, its the switch...The wire terminals are dirty an adding resistance to the circuit, and the added resistance is making it get hot.". I'm in a predicament here, because I see this as an opportunity to train the new guy on the use of the test equipment and the theory of Ohm's Law. I also know that the preceding statement "the added resistance is making it get hot" was dead WRONG and totally demonstrated a lack of understanding of Ohm's Law. (Some of you guys might even argue the same thought as he, but the real Elmers here will know that this statement is 180 degrees wrong. Now, The first thing I said to my coworkers was, "Indeed, the switch most likely IS the problem, but it might also be a short somewhere". I said this in as polite a way as possible to prevent the appearance of argiung with the other technician in front of the trainee. AND INDEED, I MEANT WHAT I SAID. I know that the switch may be the problem, but not for the REASON that he stated, which is the point! Again, he said "No, you are wrong, its the switch, dirty connections will cause resistance and the resistance will cause a voltage drop and make it get hot. Resistors consume voltage and get hot." Again, I politely said that the switch may be causing the problem, and it might be the dirty contacts, but NOT because of resistance. At this point, I was more determined to properly educate the "young skywalker" on Ohm's Law rather than be diplomatic. You see, my coworker is one who flies on autopilot. He knows how to fix a lot of things, but he doesn't always understand the reasons for the failure. He has never been interested in learning anything past the no-brainer approach, and relies totally on past experience. When confronted with a problem that lies outside of this "box", he has trouble. My coworker is my friend, and I always try to be polite and nonconfrontational, but on occasion, we agree to disagree. However, I do not want the new guy to learn things incorrectly. So, here is what I contend. The connections on the switch were kind of dull, but not extremely so. They were not particularly pitted, just discolored. What I contend is that arcing is occuring at one or more of those contacts. They are spade type connections and you know how they get loose over time. But of this, I am not totally sure. I also mentioned that the heater element might be warping and thus changing its operating impedance or partially shorting to ground. I also mentioned that the solid state relay may be intermitently shorting to "full on" instead of pulsing the heat as its supposed to do, and thus, the avarage current and power it has to dissapate is more at times. This is not likely, but a possibility to consider. Also, the control circuit might have a component that is faulty and creating a partial short. Bottom line, Ohm's law requires us to understand that LOW SERIES RESISTANCES allow higher current draw, THUS, more total power and heat. High resistances cause less current draw by the load and thus less heat and power to be dissapated. A potentiometer, if one suitable to handle 15 amps were put in series with the heater, would be HOTTER WHEN THE RESISTANCE IS NEAR ZERO OHMS and COOLER WHEN THE RESITANCE IS IN THE HIGH HUNDREDS OR THOUSANDS OF OHMS. I explained all of this to the two guys I am working with, and I kept getting arguments about how resistors consume power...which is true, but not in the way this fellow is trying to fabricate in his mind. He also tried to go into the nature of wire gauges, and said the thinner (higher resistance) wires will get hotter than fatter because of the resistance. Again, another misconception...we all know it is the surface area and heat dissipation properties of smaller gauge wires that make them unsuitable for high currents. Anyway, I could not detect a short with my amp-probe in the circuit, which is a shame, because it may reinforce my friends misunderstanding and also make me lose credibility with the younger guy. As I said, I never argued that the switch wasn't the problem, and even described HOW it might be causing it. There may even be another explanation that I can't think of, and someone smarter than I can provide. But I think this is a very common misunderstanding of Ohm's Law, and I hope that the nature of my posting will help clear some things up with others who may not understand.