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Bought this as a cost effective device to check earth leakage on badly configured CU that was tripping all the time. It gives an indication of unbalance, but it seems to be way to high to be accurate. Normal single wire AC current seems to be reliable. DC current readings are useful but again, as another reviewer noted, vary quite alot on small currents. The 'Live' check needs the operator to hold the unit as it appears to require a capacitive earth connection - like the neon testers but with a less tingly current! IE you can't use the probe and leave the unit on the bench. The extra flanges for holding the probe for 'Live' testing can get in the way in tight spaces. I may have to cut them down... Overall, though, nice tool for the price.
Although the resolution in DC clamp mode is 1mA, movement in earth's field will causes the reading to change by roughly 50mA, and the drift in reading is a few mA in 10 seconds. Luckily the reading I was after was in the hundreds of mA, so as long as the orientation didn't change much between the act of setting zero and the reading being taken, and as long as it was done in less than 10 seconds I could just about use the instrument.
Purchased to do power surveys on electrical panels. Also hoped it would give some representative signal for 4-20mA, but not expecting much. Compared to other low cost DC amp clamps (Uni-T-211B, Extech 380950) in DC AMPS this clamp meter does not read a reliable value below ~100ma and reading counts up about 1ma/second, so becomes more unreliable with time. UniT and extech will read 4-20mA in ideal (desktop) conditions but are not useable in the field as reading changes with orientation and stray fields. This meter does not show a representative value below 100ma even in ideal conditions. even at higher currents (1-10A) the ACM91 is not as accurate as other clamp meters. Tested all meters using fluke calibrator as source. Also it is not a good idea to have a uA setting using cables on a meter. If connected to voltage source, then turn on the meter you pass through the uA setting to get to volt setting, most likely blowing the fuse. The reason to get a clamp meter is to NOT have the opportunity to cause damage to self from misuse of amp setting.