Okay, okay! I get it. Let me give you some background info. Many, many, many years ago my first long term job after graduating high school was as an electronic technician at the Boeing Co. I learned all about volts, amps, ohms, farads, and other related stuff. I learned how to use multimeters, oscilloscopes, circuit tracers, differential voltmeters, and various other test equipment. After eight years I left that job and eventually wound up in the Army where I spent over 30 years involved in aviation and aircraft maintenance management and maintenance test pilot instructing. Over those years I have continued to dabble in electronics, avionics, and electrical stuff but I have to admit I have not kept up with all of the technological advancements over the last forty or so years. I have a clamp-on AC ammeter in my toolkit and use it frequently. What makes the thing work is the fact that AC current reverses its direction of flow 60 times every second (60 Hertz). (BTW, when I learned this stuff it was called "cycles." Hertz came along much later. That just shows you how long ago it was.
) Every time it changes direction it creates a magnetic field that expands and collapses around the conductor carrying the current. It is this expanding and collapsing magnetic field that is detected by the iron core of the clamp-on meter and it generates a micro-voltage that is directly proportional to the amount of current flowing in the conductor and can be read on a meter. DC current, on the other hand, flows in a steady state in only one direction and does not create that expanding and collapsing magnetic field except when you turn it on and turn it off. A clamp-on AC ammeter simply will not measure DC current and I was totally unaware that such a thing as a DC clamp-on ammeter even existed.
I checked that link that Javi posted and found only one feedback report and it was not very favorable. But my interest was piqued because I have been dealing with some 12 volt issues in my trailer where I could certainly use some accurate information about current flow. I check Amazon and found several listed there with various amounts of both positive and negative feedback. I was hesitant to order one because of the hassle of returning it if it did not meet my expectations. So, I went shopping at Lowe's (my go-to place for just about everything). I came away with a Southwire 21050T True RMS AC/DC Clamp Meter. I have had a chance to make a few measurements with it and it seems to be fairly accurate. I am pleasantly surprised. I have no idea how this thing works. It is smoke and mirrors to me. Apparently the test instrument geniuses have figured out some way to capture that steady state magnetic field and measure it.
So, bottom line is, I'm now a happy camper with a new toy. Thank you guys for enlightening me. It's amazing what you can learn on these forums.