Inverter Monitoring & Canceling Meter Legs [RE-wrenches]

[Doug Pratt]

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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