Does the energy (kWh) have a maximum count where it rolls over to zero?

The WattNode® for LonWorks®, the WattNode BACnet®, and Modbus models do have energy rollover points. The WattNode Pulse just generates pulses, so any rollover would be determined by the device accumulating the pulses.

WattNode BACnet and Modbus Models

100,000 MWh (100 GWh) is the rollover point for the WattNode BACnet and Modbus meters, at which point, the energy will rollover back to zero and start accumulating up again. Some of the energy registers can also display negative energy values, so if the energy reaches -100,000 MWh for these registers, it will rollover back to zero. The rollover applies to both the integer and floating point registers.

This rollover behavior applies to all registers whose names start with Energy.

Writing “1” to ZeroEnergy (1620) resets most of the energy registers to zero. There are three registers—EnergySumNR, EnergyPosSumNR, and EnergyNegSumNR—that cannot be reset to zero; however, they will rollover to zero at 100,000 MWh like all the others.

The WattNode BACnet and Modbus ErrorStatus objects or registers can be used to detect rollovers. The most recent eight messages are preserved in the ErrorStatus registers and there are unique codes for a rollover of each energy register. For example, if EnergyPosSum rolls over, ErrorStatus will report 96.

WattNode for LonWorks and Logger (–L) Option

100,000 MWh (100 GWh) is the rollover point for the WattNode Plus and WattNode Logger for LonWorks models (WNC series), at which point, the energy will rollover back to zero and start accumulating up again. nvoEnergySum and nvoEnergySumNR can also display negative energy values, so if the energy reaches -100,000 MWh for these variables, it will rollover back to zero.

This rollover behavior applies to all energy network variables.

Writing “1” to nviResetEnergy resets most of the energy variables to zero. There are two variables—nvoEnergySumNR and nvoEngyPosSumNR—that cannot be reset to zero; however, they will rollover to zero at 100,000 MWh like all the others.

WattNode for LonWorks – WNB Series, Option B

The WNB series WattNode for LonWorks are no longer in production, but many are in service. Also, the new WNC series WattNode for LonWorks models can be ordered with Option B which specifies that they emulate the WNB series models.

All these versions have a rollover point of 1,000,000 MWh (one terawatt-hour). They do not accumulate negative energy, so there is no negative rollover point. Also, they do not have any mechanism to reset the energy.

WattNode for LonWorks – WNB Series Integer Outputs, Option BI

The WNB series WattNode for LonWorks with optional “Integer Outputs” are no longer in production, but many are in service. Also, the new WNC series WattNode for LonWorks models can be ordered with Option BI which specifies that they emulate the WNB series models with integer outputs.

These “Integer Outputs” versions have a rollover point of 50 MWh (50,000 kWh). They do not accumulate negative energy, so there is no negative rollover point. Also, they do not have any mechanism to reset the energy.


Keywords: rollover, roll over, wrap around, overflow