Author Topic: 120v set up - phase A or B  (Read 3615 times)

tedbahamas

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120v set up - phase A or B
« on: August 04, 2011, 03:41:32 AM »
Hi,

does it matter if the black wire is hooked up to phase A or phase B?

Thanks.

GAR

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Re: 120v set up - phase A or B
« Reply #1 on: August 04, 2011, 04:03:05 AM »
110803-1940 EDT

tedbahamas:

No. How would you define phase A as distinguished from B? What is the reference you want to use for the definition? You can define B relative to A, C relative to A or B as you choose, etc.

What appears to be important is that white and black are connected to a 120 V source (not 208 or 240), and that white connects to neutral.

The reason that a negative power is not displayed is that the absolute value of power is created instead of a signed power. Probably to avoid having to flip the power polarity as a result of which phase white and black are connected to. I am not sure what is the real function of the red wire. It could actually use the 240 as the voltage and phase information for power calculation, and this would simulate what the power company does. But there is usually little difference between the voltages of the two phases. There are a lot of factors that influence total energy measurement, and the voltage difference between the two phases may not be the most critical.

You must use the white wire or there would be no power to the small transformer in the MTU.

.

tedbahamas

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Re: 120v set up - phase A or B
« Reply #2 on: August 05, 2011, 04:16:44 AM »
Thanks for the info Gar. Much appreciated.  8)