Do Canceling Meter Legs Work with Form 12S meter? [RE-wrenches]

[Kirk Herander, VSE]

A "5 jaw" meter is a form 12S, what I/we are trying to do is measure actual
solar generated AC, regardless if used for critical loads downstream from
the Trace, or to house loads/ grid upstream from the Trace, using a standard
120/240 three wire form 2s meter, and I don't think it will work.
Please reference www.hialeahmeter.com/diagrams.htm . You will find internal
schematics for both a form 2S and 12S meter. The 12S does indeed have a
neutral connection to the 5th terminal, and the meter looks like it has an
extra coil in it.

I've rewired the 2S socket before to measure 120 in one direction only by AC
hot going to Line 1, load 1 and load 2 jumpered together, and the load to be
measured going to the Line 2 terminal. Per Hialeah's instructions, for this
to work a neutral connection has to be made to the "jumper" side of the
neutral tab on the back of the meter with the tab open. I don't understand
how, but it does work.

I have measured "complete" Solar made AC in the past by doing the following:
Do not wire the critical load panel directly to the inverter's output. Place
an Auto transfer switch between the inverter and critical loads. So
criticals won't be powered through the inverter unless there is a power
failure. This way all solar AC must travel back through AC1 in circuit.
Place a form 2s meter, wired for 120 vac measurement, with detent, on the
AC1 line. And you can get fancy and measure grid ac for charging by wiring a
second meter in series, one meter seeing the grid as the line, one seeing
the inverter as the line, and their respective load outputs connected
together (both meters have detents). Solar AC will accurately be measured,
except in times of daytime power failure when the PV's are helping to
support batteries and critical loads. This works fine, but adds cost and
complexity, so.......

Can a single, form 12S meter be used to accomplish the same thing, if wired
per previous suggestion below?

>Simple. Using a standard 240v utility meter, wire the 120v leg from
> the
> SW output to the subpanel so that power passing to the subpanel spins
> the meter forward. Wire the other 120v leg so that power passing from
> the main panel to the SW input spins the meter backwards.
>
> If the SW is simply passing utility power straight thru to the
> subpanel,
> you'll have no meter action. The two currents cancel each other out. If
> the SW is pushing solar power to the subpanel, the meter spins forward.
> If the SW is pushing solar power to the subpanel *and* the utility, the
> meter spins forward faster.
>
> This ought to still work just fine with a ratcheted meter so that night
> time battery charging isn't deducted.


Vermont Solar Engineering
North American Board of Certified Energy Practitioners Certified Solar PV
InstallerT
Xantrex Certified Dealer Charter Member
Kirk Herander
PO Box 697
Burlington, VT. 05402
www.vermontsolar.com
www.backeastsolar.com
800.286.1252 - 802.863.1202
fax 802.863.7908

----- Original Message -----
From: "Christopher Freitas --- OutBack Power" <cfreitas at outbackpower.com>
To: <RE-wrenches at topica.com>
Sent: Tuesday, January 20, 2004 3:58 PM
Subject: RE: Do Canceling Meter Legs Work? (Was Re: ratcheting cyclometers)
[RE-wrenches]


> This trick of using a 240 VAC meter for a 120 VAC system with the input
> and output flowing through the two legs in opposite directions does work
> - I did it years ago on some of the first grid-tie SW systems - but I
> remember using the type of meters which included a neutral tap - which
> must have been the "5 jaw" type. I think there might be a way to wire
> into the little 120/240 jumper on the back of the regular 4 wire type
> meters - but I am not sure...
>

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