Author Topic: Inaccurate energy usage readings  (Read 6609 times)

aisbell

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Inaccurate energy usage readings
« on: January 23, 2012, 12:50:44 AM »
Our condominium complex has a single commercial electricity account with the local power company.  Submeters measure the electricity usage for each apartment.  These submeters are read monthly with each apartment owner being billed for his energy usage.  There have been problems with the sub metering system resulting in incorrect readings for some apartments which is why I purchased my TED 1000 at the end of 2007.

Since then, my TED 1000 has consistently measured our electricity usage to be about 14% less than the amount that we have been billed.  Based on this, I challenged the submetering company on the accuracy of their sub meter.  They installed an additional check meter on the circuit for our apartment.  They reported that this additional meter reported exactly the same usage as their regular meter.  They suggested that my TED 1000 must not be working correctly.  I reported this problem to Energy, Inc., but the problem was never resolved.

After all these years, I may have discovered the problem.  I noticed that the A/C in our apartment runs on 208 rather than 240 volts.  I now suspect that our power may be 208Y/120 VAC 3 phase rather than 120/240 VAC 1 phase.  The TED 1000 user guide states that the TED 1000 "is only suitable for use on 120/240V single-phase 60Hz services" and "if you have a 3-Phase service, TED Model 1001/1002 WILL NOT work."  If the TED 1000 is expecting 240 VAC but our power is only 208 VAC, that's about 13% less which is almost exactly the error that I've been experiencing.

When the user guide says that the TED 1000 "WILL NOT work" with 3-phase power, does that mean that its readings would be ~13% low?  Is there a TED meter that works correctly with 208Y/120 VAC 3-phase power?  How can I verify that our power is 208Y/120 VAC 3-phase?

RussellH

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Re: Inaccurate energy usage readings
« Reply #1 on: January 23, 2012, 01:34:38 PM »
How can I verify that our power is 208Y/120 VAC 3-phase?

If you have a volt meter and know how to do it safely, you can measure it, either at the panel or at a "220" outlet.

Does the TED 1000 measure voltage?  What is it reporting?

rotus8

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Re: Inaccurate energy usage readings
« Reply #2 on: January 23, 2012, 07:02:11 PM »
The real problem is that the TED system does not work when the two 120v legs are not 180 degrees out of phase. With a 208Y connection, the legs are 120 degrees out of phase and the TED will compute power factor incorrectly, resulting in inaccurate power readings. TED has been talking about releasing a 3-phase version for a long time, but has not been forthcoming with it yet.

aisbell

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Re: Inaccurate energy usage readings
« Reply #3 on: January 27, 2012, 04:34:56 AM »
The TED reports the voltage of its display unit, ~120.  The voltage between our two hot main panel wires is ~207 rather than 240, so ours must be 208Y/120 3-phase power.  rotus8's explanation that the phase difference of these two wires is 120 rather than 180 must explain the power measurement inaccuracies that I have experienced with my TED.  So I've uninstalled my TED and will be selling it to someone with the more common 120/240 household power  :(

Thanks for your help!