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Troubleshooting WattNode Pulse Meters


This article is a step-by-step troubleshooting guide for WattNode® Pulse meters. It assumes that all the electrical and current transformer (CT) connections to the meter are wired up, that the line voltage is turned on, and the load being measured is drawing current.

DANGER – HIGH VOLTAGE HAZARD

WARNING These instructions are for use by qualified personnel only! Lethal high voltages are present on the green terminal block. Exercise care not to short out adjacent terminals or short them to neutral or ground when connecting test probes to the screw top.

Problem Categories

Problems with WattNode meters typically fall into one or more of the following categories:

  • Wrong meter model—the meter’s electrical specs do not match the electrical service being measured.
  • Electrical connections—the voltage, neutral, or ground connections on the green terminal block are miswired or missing.
  • Current Transformers—the CTs are miswired, not connected, or installed on the wrong phase conductor.
  • Pulse output connections—miswired, reversed polarity, or incorrect count.
  • Monitoring device—pulse input not compatible, reversed polarity, or wrong scale factor.
  • Electrical Load—turned off or in low-power mode, low power factor, mis-estimated load, VFD noise.

When a WattNode Pulse meter does not appear to be operating correctly or generating expected pulses, the first step is to observe the three status LEDs on the front of the meter. When the meter is first powered up, all three LEDs should light up in a red, yellow, green sequence. Then, if everything is working properly and the load is drawing power, the LEDs will begin to flash green. The rate of flashing indicates the relative amount of power. See Table 5: LED Flash Rate vs. Power in the manual.

When there is a problem, the first thing to do is to refer to the appropriate wiring diagram in the WattNode Pulse Installation and Operation Manual (Manual). Check that all the connections are correct and that the screws on the terminal blocks are tight. If no wiring errors are found, refer to the appropriate diagnostic table below:

LED Status Lights

Symptom Details
All LEDs Off If none of the LEDs light up, check:

  1. All the connections on the green terminal block are connected to the electrical service and that the power to the meter is turned on.
  2. Use a volt meter to verify that that the correct voltage is present on the ØA, ØB, and ØC terminals. Refer to Table 1: WattNode Models in the manual for the proper voltages for each model of meter.
Red Flashing Indicates negative power (power flowing into the grid). This could be normal in a bidirectional power measurement application, such as a photovoltaic system, where negative power occurs whenever more power is generated than consumed.If all three LEDs are flashing red and turning on and off together, this could indicate Low Line Voltage or that the meter is experiencing an internal error. If the flashing is not perfectly synchronized, that indicates negative power.

A current transformer (CT) on the phase flashing red may be installed in the wrong direction, the white and black wires maybe reversed, or the CT is installed on the wrong phase conductor. In some cases, flashing red can indicate that the CT wires are connected to the wrong CT inputs. For example if the phases B and C wires were swapped.

When one or more LEDs are red check the following:

  1. Are the CTs installed on their corresponding phase conductor? Is the ØA CT on the same conductor as the ØA voltage connection, etc, ect.
  2. Are the CTs installed with their arrow or label ‘THIS SIDE TOWARD SOURCE’ facing towards the source of power?
  3. Are the CTs connected to the correct phase on the screw terminals? And are their white and black leads connected to the corresponding white and black terminal as indicated by the white and black circles on the on the WattNode label?
Erratic Flashing If the LEDs are flashing slowly and erratically, sometimes green, sometimes red, this generally indicates one of the following:

  1. Earth ground is not connected.
  2. Voltage is connected for a phase, but the current transformer is not connected, or has a loose connection.
  3. Electrical noise can cause erratic flashing especially when there is no load or very small load.

When one or more LEDs are flashing erratically check the following:

  1. Is the earth ground is connected?
  2. Are unused current transformer inputs shorted out?
  3. Are unused voltage inputs connected to neutral (if present) or to earth ground?
  4. If noise is suspect, try increasing the load. If erratic flashing persists try moving the WattNode meter away from the noise source. Also keep the CT wires as short as possible by cutting off excess wire.
Other Conditions Refer to the Installation LED Diagnostics section of the manual for a more detailed explanation of the flashing color patterns.

Current Transformers

Symptom Details
The measured current exceeds the CT rating. This can saturate the CTs or the WattNode input circuitry, resulting in lower than expected readings. If possible, use a clamp-on current meter to measure the current and make sure it is below the CT rated amps.
The measured current is too small The accuracy of most current transformers is only specified from 10% to 100% of rated current. In practice, most CTs work reasonably well down to 1% of rated current. Very low currents may not register properly, resulting in low or no output pulses.
No voltage at CT terminals With current flowing in the conductor that the CT is installed on, measure the voltage between the black and white wires. Probe directly on the top of the terminal screw with a meter set to measure millivolts AC (mVac). With the full scale rated current of the CT flowing in the conductor the voltage should be 333 mVac. See CT Output Voltage Test.If no voltage is measured, loosen the terminal block screws and remove the wires. Check that 1/4′ (6 mm) of insulation has been stripped from the ends of the wires. Twist the bare wire strands together, insert into the terminal block, and tighten the screw.
Interference (noise) from a VSD or inverter Generally, variable speed motor drives should not interfere with the WattNode meter, but if they are in close proximity, or if the CT leads are long, and / or run in parallel with electrical conductors they may pickup interference from the VSD. Try moving the WattNode meter at least three feet (one meter) away from any VSDs or other noise sources. Keep the CT leads as short possible and do not run them along side of conductors. NEVER install a WattNode meter downstream of a VSD—the varying line frequency and extreme noise will cause problems!

No Pulses

Symptom Details
No pulses and green flashing LEDs Flashing green LEDs indicate that the WattNode meter is measuring positive power and generating pulses on the P1 output. If the monitoring device is not reading pulses, check the wiring and make sure that the that the polarity is not reversed. The P1 terminals must be connected to the positive input on the monitoring device. Some devices may need a pull-up resistor and/or external voltage source. See the Connecting Pulse Outputs section in the Manual.The pulse outputs can be tested using a multimeter set to measure ohms. Remove the wires on the pulse output terminal block and connect the positive lead of the meter to P1 and the negative to COM. If pulses are present, the meter reading will alternate between a high and low resistance reading. Note that if the power level is very low it may take several minutes for the output to change.
No pulses and red flashing LEDs If the WattNode meter is a bidirectional model, flashing red LEDs may indicate negative power, in which case energy pulses are generated on the P2 output. In model without bidirectional outputs flashing red LEDs may indicate that one or more CT are installed backwards. See the LED Status Lights table above.

See Also

Keywords: diagnostics, testing, low power factor, VSD noise, VFD noise, status LEDs