Inverter Monitoring & Canceling Meter Legs [RE-wrenches]

[Joel Davidson]

Wrenches who have been doing utility intertie PV probably know a few
utility technicians who work in the Meter Section who can answer your
questions. There's almost always a Meter Section tech who likes to share
his knowledge or has the time to figure out different ways to hook up
meters.


> [Original Message]
> From: Doug Pratt <dmpratt at sbcglobal.net>
> To: RE-wrenches at topica. Com <RE-wrenches at topica.com>
> Date: 2/14/04 2:20:27 PM
> Subject: Inverter Monitoring & Canceling Meter Legs [RE-wrenches]
>
> Folks,
>
>   I have to admit I'm kind of amused. Here we are, a large group of
> highly experienced, innovative electricians...and nobody's clear on how
> to wire a standard utility meter. But until the past few years, standard
> AC watt-hour meters just weren't part of "renewable energy."
>
>   Last month I proposed a meter wiring scheme for battery-based,
> grid-tied systems (like an SW or Outback) that had grid AC input passing
> thru one leg of a standard 4-contact meter, and inverter AC output
> passing in the opposite direction thru the other leg. Straight pass-thru
> power from the grid to the loads would be ignored, the two currents
> cancel each other out. But any renewable power input or grid power use
> by the inverter would be registered accordingly. Considerable, but
> inconclusive discussion ensued...we need hands-on experience, which I've
> got now.
>
>   It Works. With inexpensive, standard 4-contact J5 type meters, it DOES
> work. I currently have two of them running. One is monitoring a Trace
> SW5548, the other is monitoring an Outback GVFX3648 (serial #GFX00001,
> thank you very much Robin and Christopher!) The only trick is when
> running an AC meter on 120vac systems, there's a small pair of screws on
> the back of the meter holding down a connection tab. Loosen them, rotate
> the tab open, and run a ground or neutral wire to the screw with the
> captive tab. (Caution, the other screw is connected directly to one of
> the power contacts.) 
>
>   I'm running cheap rebuilt Hialeah meters, two different mfr. brands.
> One's a GE, the other's a Sangamo(sp?). They run backwards when the
> inverter is selling power, forwards when the inverter is battery
> charging, and don't move at all at night when the inverter is simply
> passing grid power directly to the loads. It's a simple solution folks.
>
>   Why do I have an Outback and a Trace SW on my wall? Why do I have two
> matched PV arrays feeding two MX60 controllers and two matched Concorde
> battery packs? You can probably guess, but the official answer has to
> wait awhile...I promised Christopher he could break the news, and we
> just started collecting data this morning. :-)
>
> Cheers,
> Doug Pratt
>
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