Howto measure 480V WYE 3-phase reference voltage?

[overeasy]

Hello Dave,

The good news is that you are not on the bleeding edge. The manufacturing plant where IoTaWatt are produced has 480V/277V three phase and we have an IoTaWatt monitoring the main panel.

Industrial 277V/480V three-phase

Over the past month or so, I’ve been working with the manufacturing facility to install an IoTaWatt on the primary service of the plant. They recently upgraded their service from 600A to 800A, so given the shutdown that would require, it was a prime opportunity to install some CTs and have the electrician install an IoTaWatt. The first technical challenge was sourcing VTs for 277V. I found a 277V:12V model manufactured by Axis corp (AX-27750-H) that works fine. I calibrated three samples and …

I see the AX-27750-H is currently available on ebay. It’s also availabl;e as an ELCO ETR12-277 from Amazon, and several electric supply online (google it).

As in the pictures in the post above, they mount to a standard hole in a wiring box. The secondary (12V) are just wire leads, so you need to attach a cord with 5.5mm x 2mm barrel plug (like the other VTs).

You can use three, or just one for derived reference. Yes, you can split the transformer output with a commercial CCTV splitter cord. It is imperative that you observe consistent polarity when splitting, and the commercial splitters pretty much insure that as they are made for DC where polarity is less forgiving.

If you share AC reference between IoTaWatt base units, it is critical that each base unit have it’s own USB power supply.

The above transformer is already in the VT tables as AX-27750-H. I would however recommend calibrating after installation as with limited experience I don’t how much variation there is.