Electrical Installation

Why is the meter reporting more power used than it should?

It is very unusual for a meter to report more than it should.  We have seen instances where a bad neutral has made a meter advance as fast as the display was able to keep up and tens of thousands of KWH are recorded in a matter of hours.

A meter can record more power that it should if the wire through the CT is looped back and run through the CT multiple times.

The most common cause of a tenant complaining about an inaccurate meters is a neighbor who uses a lot less power.  The best way to handle this is to swap the meters between the two units and see if power usage remains about the same of if the consumption changes dramatically for both tenants.

The meter can be returned to the factory for an accuracy test for a charge of US$30 plus shipping.

What is the Phase Matching Alarm?

This applies only when power is supplied from a three phase transformer.

Be sure to turn off power to the meter before making any of the changes suggested here.  It is very easy to blow a meter if working hot.

The voltage and current references for the meter must be properly matched or that phase will only report half the power actually used.  This means that if the wire that goes through CT1 is not connected to the VAC1 voltage input, half the power used will not be recorded. This happens because the two phases are 120 degrees out of phase and the meter sees it as 0.5 power factor.  With a single phase transformer, the two legs are 180 degrees out of phase which causes an insignificant error.

The alarm causes the red LED on the meter to flash about once a second.  It will happen whenever the meter senses negative power and a power factor below about 0.8.  It needs about 60 watts flowing through each leg for this to happen. If you see the alarm, the first thing to check is that the CTs are on in the right direction (label toward the load).  If it is not and the load is causing a low power factor, the alarm will be active (flashing). Swapping the black and white CT wires should fix the problem rather than having to remove the CT.  Having the CT on backward also disables the alarm to that it will not activate if the phases are not properly matches.

If the alarm is active and the CTs are all in the right direction, it means that at least two of the CTs are not properly paired with their voltage inputs.  Turn off power to the meter then reconnect the CTs after properly tracing the wires.

The meter seems to not be reporting all the power used. What could be wrong?

A number of things could be wrong:

  1. Make sure the meter is running.  The red LED at the top should be on and bright.  A dim LED can indicate a loose connection for either the power or the neutral.
  2. All the wires may not have been put through the CTs.
  3. Some of the wires may have been put through the CT’s backwards.  If there are multiple wires through a CT, this will cause the meter to report the difference between the two wires instead of their sum.
  4. Wires from two different legs may have been put through the the same CT. This will also cause them to subtract from each other.
  5. On three phase systems, even if only two phases are being used, not matching the current and voltages properly will cause the meter to report half what it should. See Phase Matching Alarm for details.
  6. All the hot wires need to be connected to the meter.
What direction is right for the CTs

The current transformers (CTs) should be installed with the label facing the load.  But for most users, it doesn’t make any difference.  The meter will report accurate power usage either way.  But for some users, it does make a difference

  1.  If the power comes from three phase transformer, the CTs must be installed properly for the phase matching alarm to work.
  2. For smart meters, positive power (watts) will be reported as negative power and positive accumulated power (kwh) will be reported as negative.


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