This box followed me home as a freebie from a garage sale and seems to to work well. Other than what you can see in the picture it's got no manufacturer or ratings on the box. I've run a few amps through it with no problems. All it's got inside is the sense coil/transformer for the amps reading and two small transformers feeding power supplies for the two meters.
The picture is the load for the 10,000 BTU AC unit in the office. It shows a 6 volt line drop with the compressor running (10 amps avg) compared to fan only.
That reminds me of a demonstrator for one of those 'motor economizer' devices. Sometimes you see them in a hardware store with a motor plugged in and throwing the switch kicks the thing in and out and you can see the amp draw change,
I think you're right, the labeling suggests it too. The guy that got it got a 1/4 HP motor in the same box along with this.
I don't know how far I could turn down the input voltage with a variac before it would interfere with the power supplies for the meters; I suppose I could power them separately. I still prefer direct analog metering.
