Author Topic: 240V measurements?  (Read 2732 times)

energyrabbit

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240V measurements?
« on: March 03, 2013, 11:41:12 PM »
Just hooked up a TED 5000c to a single phase panel and love it!  There is one thing that I wanted to understand though..

we have a 240V 10KW rated electric heater, which is wired between/across both legs for 240V.  When the heater runs, TED registers over 20KW! is this double counting/adding the demand as the load occurs across both legs? and more importantly how does the utility company measure demand? 

In my understanding, the rated power of 10KW is independant of the voltage, and in the single phase configuration would be distributed across both legs, so (L1+L2)120/1000 = 10KW (L1 + L2 = 83 Amps)

so 10KW  would be about 40Amps/5KW per leg but not 20KW..




I'm troubleshooting the demand as we have been billed for over 22KW peak demand, when all of the devic ratings present in this panel don't even come close to adding up to that.  (heater is 10KW, plus lights etc don't come to more that 15KW).



Thanks!


« Last Edit: March 04, 2013, 12:42:52 AM by energyrabbit »

Support7

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Re: 240V measurements?
« Reply #1 on: March 04, 2013, 08:24:07 PM »
Good Morning Energyrabbit,

Do you have your black and red MTU wires connected? Have you checked your MTU connection type in Footprints to make sure it matches your configuration?

You can also submit a ticket at www.theenergydetective.com/new-ticket  and one of our Support Techs will be able to walk you through some troubleshooting steps to determine what is going on with your system.

Thank you,

TED Forum Support
www.theenergydetective.com/new-ticket

RussellH

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Re: 240V measurements?
« Reply #2 on: March 04, 2013, 09:18:19 PM »
we have a 240V 10KW rated electric heater, which is wired between/across both legs for 240V.  When the heater runs, TED registers over 20KW!

Is that a 20KW increase when it's turned on or 20KW total?  A 20KW total might be right if the rest of the house is drawing 10KW when you turn on the heater.


is this double counting/adding the demand as the load occurs across both legs? and more importantly how does the utility company measure demand?

Yes, it's double adding two 120V legs - that gives it the same power as single-reading one 240V.  So it all works out. 

240V * 41.7 = 10KW
(120V * 41.7) + (120V * 41.7) = 10KW
 

In my understanding, the rated power of 10KW is independant of the voltage,

Not sure what you are talking about here - power is most certainly a function of voltage.  I don't believe heaters are capable to adjusting their current to match rated wattage when the voltage changes.  They will draw rated wattage when connected to rated voltage.

As support suggests, if you've connected both power leads of the TED but have the voltage setting in TED set differently that would most certainly cause a power miscalculation.

matt1001

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Re: 240V measurements?
« Reply #3 on: March 04, 2013, 11:30:01 PM »
I'm guessing it will read double if you hooked up both the black and red wires from the MTU but set the System Layout to 120V instead of 120/240V

Does your voltage read as 120V or 240V?

energyrabbit

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Re: 240V measurements?
« Reply #4 on: March 06, 2013, 08:43:27 PM »
Thanks!  I had the setup wrong, and the software was configured to 1 unit (white wire only), 240v.  when I picked the correct configuration to match the installation, of red/white 240v/120v now the heater reads 10KW when running which is par with it's rating ;)

yay!