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WND-WR-MB-Inst-1.03
The standard meter supports CTs with a 0.33333 Vac output (one-third volt). With the correct op-
tions, the meter can support CTs with a 40 milliamp output: contact CCS for details.
3.4.1 Current Transformer Installation
Selecting Current Transformers
for information on selecting appropriate cur-
rent transformers (CTs).
●
WARNING:
To reduce the risk of electric shock, always open or disconnect circuit from power-
distribution system or service of the building before installing or servicing current transformers.
●
WARNING:
When using UL Recognized CTs, they must be installed on insulated conductors
only and maintained away from all live parts.
●
Do not
use 1 amp or 5 amp current output CTs!
●
The CTs are not suitable for Class 2 wiring methods and must be treated as Class 1 circuits.
●
Use plastic cable ties to secure the current transformers and route the lead wires so that they do
not directly contact uninsulated live terminals or conductors.
●
Split-core CTs can be opened for installation around a conductor. A nylon cable tie may be
secured around the perimeter of the CT to prevent inadvertent opening.
●
Do not install current transformers where they would: 1) exceed 75 percent of the wiring space
of any cross-sectional area within the equipment, 2) would block ventilation openings, or 3)
would be in an area of breaker arc venting.
●
See the CT datasheets for the maximum input current ratings.
●
To minimize current measurement noise, avoid extending the CT wires beyond 100 feet (30
meters), especially in noisy environments. If it is necessary to extend the wires, use twisted pair
wire 22 to 14 AWG, rated for 300 V or 600 V (not less than the service voltage) and shielded if
possible.
Find the source arrow or label “THIS SIDE TOWARD SOURCE” on the CT and face/point toward
the source of current. CTs are directional, so if they are mounted backwards or with their white and
black wires swapped the measured power will be negative. The power status LEDs indicate negative
measured power by flashing red.
Install the CTs around the phase conductors to be measured as shown in
Figure 1
through
above. Connect the CT leads to the meter.
For revenue accuracy, use revenue-grade current transformers; other CTs are less accurate and
may not provide revenue accuracy. Contact sales for more information on appropriate CTs.
3.4.2 CT Wiring
The current transformers connect to the six-position black screw terminal block. Connect the white
and black CT wires to the meter terminals marked
CT1
,
CT2
, and
CT3
(see
Figure 1
above). Ex-
cess length may be trimmed from the wires if desired. Connect each CT with the white wire aligned
with the white dot on the label, and the black wire aligned with the black dot. Note the order in which
the phases are connected, as the line voltage phases
must
match the current phases for accurate
power measurement. Torque the screws to 3.5 lbf·in (0.4 N·m).
3.5 RS-485 Communication
3.5.1 RS-485 Cables
There are many choices for RS-485 cabling. Ideally use cable specifically rated for RS-485 applica-
tions as it will have the best impedance for long distances to minimize interference and reflections.
However, for distances up to 100 meters, especially at baud rates of 38,400 or lower, a special RS-
485 cable is normally not required. See
for more information.
There are some common conductor configurations for RS-485 cables:
●
Two conductors without shield: we do not recommend using this type of cable because our
meter expects the common terminal to be connected.
●
Two conductors with shield: use the two conductors for the
A-
and
B+
terminals, use the shield
for
C
(common). If the shield is connected to earth, it should only be connected at the Modbus
master device.
