Hardware
Installation
13
127 mm (5.0")
143.5 mm (5.65")
85.5 mm (3.37")
32.5 mm (1.28") High
Ø 9mm (11/32")
Ø 5.5mm (7/32")
Drawn to Scale
Figure 2.7: WattNode Dimensions
To protect the WattNode’s plastic case, use washers if the mounting screws could pull through the
mounting hole or damage the case. Also, take care not to overtighten the mounting screws, as long term
stress on the case may cause cracking.
2.4 Connecting Current Transformers
The WattNode will only work with CTs containing built-in burden resistors that produce 0.333 volts output
at rated current. The use of any other CTs will result in incorrect power measurements, and may
permanently damage the WattNode. CTs with 5 amp output will destroy the WattNode and must not be
used. The WattNode’s 0.333 VAC output CTs may be safely installed around wires carrying current
because the built-in burden resistors eliminate any shock hazard.
There are two steps to connecting the current transformers: mounting each CT around the wire to be
measured and connecting the CTs to the WattNode.
The WattNode does not measure negative power and will instead indicate zero power. CTs are directional,
so if they are mounted backwards or with the wires reversed the measured power will be negative. In an
installation with just one CT, the WattNode would output zero power. In a multiple CT installation, if one
CT were backwards and others were mounted correctly, then the reversed CT would cause the power on
that phase to be subtracted from the power measured on the other phases, resulting in a plausible, but
incorrect reading.
CTs are labeled with either a label which says “THIS SIDE TOWARD SOURCE”, or with an arrow.
Mount the CT so the label faces or the arrow points towards the current source—typically the circuit
breaker for the circuit being measured or the utility’s meter box. It is also possible to measure generated
power by treating the generator as the source.
