10
Hardware
Installation
2.2.3 Three-Phase Three-Wire Delta
WARNING
This configuration is dangerous because there is no neutral wire, and as a result, the screw terminals to
connect the CTs will have line voltages on them whenever the WattNode is powered. Therefore, for
safety, it is critical that the WattNode is not powered while connecting the CTs.
This is typically seen in manufacturing and industrial environments. There is no neutral wire, just three
power lines with AC waveforms shifted 120° between the successive phases. With this configuration, the
line voltage wires may be connected to the phase A, B and C terminals in any order, so long as the CTs are
connected to matching phases. Three-phase three-wire delta circuits should be measured with the
WNA-3D-208 (208 VAC phase to phase) or the WNA-3D-480 (480 VAC phase to phase).
Source
Faces
Phase A
LINE
Phase B
Phase C
LOAD
Current
Transformers
WHITE
BLACK
WHITE
BLACK
FT10
WNA-3D-xxx-FT10
Continental Control Systems
W
ATT
N
ODE
C CT
B CT
Service
C VAC
B VAC
A VAC
Figure 2.3: Three-Phase Three-Wire Delta Connection
The three-phase delta configuration may require larger current transformers than expected. For balanced
loads, the line currents are 1.732 (the square root of 3) times larger than the phase currents. For example, in
Figure 2.4
below, if phase currents
i
ab
,
i
bc
, and
i
ca
are each 100 amps, then line currents
i
a
,
i
b
, and
i
c
are
each 173.2 amps. This circuit would therefore require CTs rated for at least 175 amps. When choosing the
current rating for the CTs, determine if the maximum circuit current is a line current or a phase current.
