EKM Metering

I have three hots, a neutral, and a ground. Phase-to-phase voltages are 240 every which way. Neutral-to-phase voltages are 120, 120, and 208 volts. (Measured 124, 121, 211, but close enough!) I'm pretty sure this is the system described on the last page here: http://www.programmablepower.com/support...

Forgive me, DC pro, AC noob, trying to learn enough about AC to help a local hackerspace set up submetering. Our service is 240v 3-phase delta with a split-leg to provide a neutral and 120v for office loads. Coming off the pole there are just 3 wires, so I guess the neutral counts as derived, but it...

As far as I can tell from the website, the I supports higher voltages, the II supports a higher communications speed, and otherwise their specs are identical. The I is also cheaper. What am I missing? Thank you!