I ordered two of these, tested them and at first they worked almost exactly as advertised. It worked at around 180 amps, which is pretty close to 200 amps, so I was happy. I ordered another one and it worked under 100 amps (should work at 200 amps). I sent it back and got another one. This worked with a current of just over 100 amperes. I decided to keep it as I had a 100 amp circuit breaker. Update: After some use I found it to drop well below 100 amps and this is totally unacceptable. (Note that it takes some time to trigger, but after five to ten minutes it will trigger at much lower currents.)