Under Current Sensing

[JesperMP]

Actually, you can easily shave off 200 USD from that price.

But it is certainly cheaper than the AB unit.

 

[Lancie1]

Because you are in the US, you could get an SSAC brand "AC Universal Current Sensor", model ECS41BC, $65 US from Grainger.com or another distributor. This sensor has a 10 Amp SPDT relay output, with adjustable trip range of 2 to 20 amps, adjustable trip delay of 0.5 to 50 seconds, LED fault indicator, undercurrent/overcurrent selector, automatic reset, and built-in current transformer, all in a box about 4" x 5" x 1".

For a 100 HP motor, you would still need an additional current transformer to get the current down to 20 amps maximum.