30
Operating Instructions
the positive energy sum:
nvoEngyPosSum
only counts up, so that you can see the total energy
consumed. From these two values, you can compute the negative energy sum—the total energy
generated—using the following formula (the resulting value will be positive):
EnergyNegSum =
nvoEngyPosSum
-
nvoEnergySum
nvoEnergySum
This is the energy (kWh) sum of phase A, B, and C energies. This variable can count both
up and down for bidirectional or net metering applications. If you want an energy value that
can only count up, use
nvoEngyPosSum
instead.
nvoEnergySum
can be reset to zero with
nviResetEnergy
.
nvoEnergySumNR
This is same as
nvoEnergySum
, but can never be reset to zero (non-resettable).
nvoEngyPosSum
This is the
positive
energy (kWh) sum of phase A, B, and C energies. This variable only counts
up. This is updated every five seconds by adding the net energy for phases A, B, and C for
the last five seconds; if this combined total is positive, then it is added to
nvoEngyPosSum
.
nvoEngyPosSum
can be reset to zero with
nviResetEnergy
.
nvoEngyPosSumNR
This is same as
nvoEngyPosSum
, but can never be reset to zero (non-resettable).
nvoEnergyA / nvoEnergyB / nvoEnergyC
These are the per-phase energies (kWh). These values can count both up and down for bidirec-
tional or net metering applications. These variables can be reset to zero with
nviResetEnergy
.
nvoReacEngySum
This is the reactive energy (kVARh) sum of phase A, B, and C reactive energies. This variable can
count both up and down. Generally positive reactive energy indicates an inductive load like a
motor or transformer (this may not be true if you are using a variable speed drive or inverter), while
negative reactive energy indicates a capacitive load.
nvoReacEngySum
can be reset to zero with
nviResetEnergy
.
This is the reactive energy: also known as kVAR-hours. Inductive loads—like motors—generate
positive reactive power and energy, while capacitive loads generate negative reactive energy. This
variable is a bidirectional register that can count up or down depending on the sign of the reactive
power.
The WattNode meter only measures the fundamental reactive energy, not including harmonics.
nvoReacEngySum
can be reset to zero by writing “1” to
nviResetEnergy
.
Power Variables
The power variables report the real power for each phase and for the sum of all phases. They are
measured every five seconds. The WattNode meter measures power by sampling and multiply-
ing the instantaneous voltage and current waveforms at 5 kHz, so the power measurements are
accurate even in the presence of harmonics and non-unity power factor.
Power measurements can indicate positive or negative values. Unless you are measuring power
generation (as in a house with PV panels), negative power may indicate an installation problem;
see
Measurement Troubleshooting (p. 22)
