Overview

WattNode® Modbus meters manufactured prior to June 11th, 2010 reported an error condition as long as the measured power exceeded 1,000,000 W (one megawatt). This was fixed with firmware version 14.

Only the following combination of models could result in this error:

  • WNC-3Y-400-MB and WNC-3D-400-MB models with 4200 amp or larger CTs on any phase.
  • WNC-3Y-480-MB or WNC-3D-480-MB models with 3600 amp or larger CTs on any phase.
  • WNC-3Y-600-MB model with 2800 amp or larger CTs on any phase.

Details

For all WattNode Modbus (WNC series) firmware versions prior to 14, if the power for any phase exceeds one megawatt, the following things happen:

  1. The WattNode responds to Modbus master commands that request any power register (PowerSum, PowerA, PowerB, PowerC, etc.) with a Modbus ‘Slave Device Failure’ exception (04). All other registers, including energies, can still be read without causing an exception response.
  2. All three phase LEDs go to solid red to indicate a persistent error condition.
  3. The ErrorStatus registers report error code 76.
  4. As long as the power level for any phase remains above one megawatt, the WattNode computes and accumulates the energies for all phases on every other second but does not accumulate them on the alternate seconds. The net result is that the energy registers for all phases accumulate at half the normal rate during this time.

After the power levels for all three phases go below one megawatt, the WattNode returns to normal operation and resumes accumulating energy at the proper rate.

Fix

If you have a WattNode Modbus with firmware version below 14 and you may encounter power levels in excess of one megawatt, then return the WattNode to Continental Control Systems LLC for a free firmware upgrade. To determine your firmware version, see WattNode Modbus Firmware Versions.