Since most of my postings are based on the phone calls I receive from “technicians” in the field or at job sites, I feel compelled to write this blog about basic Electrical Troubleshooting.
Let’s start with a few examples of the calls —
The other day I had a technician who was ready to condemn a 3-phase compressor because it would try to start and then trip the internal overload. When I questioned him on his “power” to the compressor, he said it was good(?). When I asked him what good was, he said he had 230 volts. I asked how he checked it and he said, “I have 230 volts between all the terminals on the contactor”. When I asked what he had from each terminal to ground it turns out, he was missing 1 leg of power due to a blown fuse. He didn’t realize that he was reading a “back feed” through the windings on the “pairs”. When he replaced the fuse, the compressor started and everything worked fine.
Then I had a technician call and he was getting a “fault code” saying a sensor was not compatible with the system. I asked him what the ohm reading of the sensor was and he said 13.2 ohms. If this was truly the case, the sensor was bad but then I asked him what scale he was on? He said, “my meter is auto-ranging”. I asked if there was a K or M on the screen and he said there was a K. Well, that means the sensor was actually reading 13,200 ohms which was a good sensor. All we had to do was re-boot the control to find the sensor since they initially started the system without the sensor and then added it afterwards and never powered down so the system looked for the sensor. This was the second sensor the technician put on the system and he was ready to condemn it also.
I use these examples to make the point that knowledge of how to properly use meters is very important to do proper diagnostics. I do carry a digital multimeter but I still carry an analog meter with selectable scales on it. They are also nice for checking a safety that “bounces” because I can watch the needle move where most digital meters don’t react quick enough. I know most guys look in wonder when I bring it out, but once I show them what it can do, and suggest they go buy a cheapo $10.00 Radio Shack analog meter, they usually do. (I grew up using a Simpson 260 and will never get rid of my analog meter).
In my next few postings, I will try to discuss how to properly use meters to make proper diagnostics.
I’m not intending to insult anyone with this basic knowledge but I see there is a need for this. Hopefully, you will not be offended by these posts and maybe remember something you learned in school that you may have forgotten. I hope you take the time to read the next few posts on this subject.