This document applies primarily to the net metering of
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With a two-meter adapter, the meter that is directly in line
residential and light commercial Class 1 installations.
with the meter socket is the normal billing meter. The
Larger
meter off to the side (or above or below) measures the
and/or
more
complex installations require a
coordinated effort between the customer, the generator
vendor and UI.
energy that the customer sells back to UI.
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meters have multiple channels that can be read by the
customer. (“Class 1 renewable” customers are provided with
ABB or Elster meters.) These meters are pre-programmed to
record energy flow in only one direction so that the energy
There are several physical constraints that must be met in order
generator applications, UI requires the use of two meters.
to use a two-meter adapter.
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One meter is used solely to record energy delivered from
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Service size is limited to not more than 200 Amps.
UI to the customer
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Existing meter socket must be of the “ringless” type. (The
flowing out of the customer’s site and into UI will not be
inadvertently charged to the customer instead of credited.
adapter will not fit properly onto a “ring type” socket.)
Second meter is used solely to record energy received
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Existing meter socket does not have a “bypass”
mechanism. (The bypass mechanism’s clamping action
The use of two meters is needed in order to assure that the
will not allow the adapter to be pushed into the socket.)
outgoing power is properly credited to the customer under all
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circumstances.
electronic meters must be used. The digital displays on these
charge for the installation.
In order to accommodate net metering for Class 1 renewable
from the customer into UI.
For net metering of Class 1 renewable generators, fully
The two-meter adapter is installed by UI and there is a
METERING REQUIREMENTS
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READING THE METERS
Two-meter adapters cannot be combined with other
adapter-type meter accessories such as a meter-mounted
whole-house surge protector.
METERING METHODS
This meter is recording energy flow. Note the arrow
pointing to the right.
There are several methods used to accomplish the two-meter
arrangement and the method chosen will depend on technical
1.
3.
The third method of connecting the second meter
applies only to 400 Amp (Metering Class 320) services.
dynamics of the application.
One method is for the customer’s electrician to install
This method involves the installation of current transformers
a second meter socket in line with the first.
(CTs) over the load side power conductors in the main meter
The second meter is used to
measure the energy that the
customer sells to UI. For
“transformer rated” metering, the
on the meter nameplate. The display on a transformer rated
meter increments at a much slower pace than that of an
equivalent self-contained meter. That is because the display on
This work must be performed as a coordinated effort between
a self-contained meter increments once for every kWh of energy
UI and the customer’s electrician. The “transformer rated” meter
while the display of a transformer rated meter increments once
measures the energy that the customer sells to UI. The
for every one kWh times the multiplier (typically 40 or 80 on
advantage of this method of net
residential meters).
metering for 400 Amp services is
mounted next to the original socket.
that it reduces the costs and
The second method is to install a two-meter adapter.
unsightliness of having two full-
This is the most common method used by
sized 320 Amp meter sockets.
homeowners with a service of 200 Amps or
However, before considering this
less.
method, the customer’s
electrician should consult with
Utility Meter
the town electrical inspector.
Generator Meter
display must be multiplied by a value that is written (in marker)
socket.
second meter socket is simply
2.
Note: For “Transformer Rated” meters, the value on the
There will be an arrowhead or a sequence of bars on the meters
that display the instantaneous direction of power flow. As you
go from importing power from UI to exporting power to UI, the
arrows will change direction. The meter with the arrow pointing
to the right is the one currently recording energy. The one with
the left-pointing arrow is recording nothing. The arrows on the
two meters should always be pointed in opposite directions.
METER DISPLAY
ELECTRONIC METER DISPLAY
CHANNELDESIGNATIONS
Meter Type
ABB / ELSTER
CH1
Date (DD/MM/YY)
CH2
Time
NET METERING
CH3
This meter is not recording energy flow. Note the
arrow pointing to the left.
(The 'generator' meter is wired backwards so that it spins
forward when you are selling power back into the UI system.)
If you want to conduct a test, while the generator is in service,
CH4
Total kWH
CH5
Rate A kWH
CH6
Rate A Demand
CH7
Rate B kWH
CH8
Rate B Demand
CH9
Rate C kWH
CH10
Rate C Demand
CH11
Program ID
CH12
try turning on electrical devices (oven, a/c, etc.) in your house
CH13
until you see the arrow on the billing meter point to the right
CH14
K' value
( ) and the arrow on the 'generator' meter point to the left
(↖). Once the above is true, start turning off electrical devices
until you see the arrow on the billing meter point to the left
Rate A = On Peak Rate B = Off Peak
Rate C = Shoulder (Not used in all cases.)
(↖) and the arrow on the 'generator' meter point to the right
( ). In each case, the total kWh reading will only increase on
the meter with the arrow pointing to the right.
The above table represents a ‘Time of Use and Demand” rate
structure. Not all channels will be utilized for all rate structures,
but the channel number of the channels that are used will still
match that of the table.
UI’s generator meter is measuring something different from the
meter provided by the generator vendor. The vendor's meter
measures the total production of the Class 1 generator system.
UI's 'generator' (we call it 'outflow') meter records only the
excess power that is back-fed to UI. The rest of your system's
CLASS 1 RENEWABLE GENERATION
(Primarily Solar & Wind)
output is used to reduce the energy consumed from UI. There is
no way to do a direct comparison between the two meters. The
best check for most people (with a prior billing history on the
same location) is to compare the kWh numbers (not dollars) on
today's bill with those from a similar prior billing period. Note:
Please consider any significant additions or removals of
electrical equipment done during the comparison period when
doing this comparison.
UNITED ILLUMINATING COMPANY
Distributed Generation
801 Bridgeport Avenue  Shelton, CT  06484
email: [email protected]
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Meter Requirements
Metering Methods
Reading The Meters & Display