# phase sequence checking for a 3phase supply

Discussion in 'Power Electronics' started by Abdul Sattar Kazi, Sep 22, 2016.

1. ### Abdul Sattar Kazi Thread Starter New Member

Sep 22, 2016
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Last edited by a moderator: Sep 22, 2016
2. ### JohnInTX Moderator

Jun 26, 2012
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Is this homework for school?

3. ### crutschow Expert

Mar 14, 2008
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What was wrong with the solutions in the referenced thread?
But this does sound like homework otherwise why the "must not use a microcontroller" statement?

Jun 22, 2012
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5. ### schmitt trigger Active Member

Jul 12, 2010
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this has worked for me.
With the proper phase sequence is connected, a 60 electrical degree pulse appears at the output. Otherwise it is a continuous high logic level.

Note, the input resistor values are sized for 208 volts L-L

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6. ### tcmtech Well-Known Member

Nov 4, 2013
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Years ago at one of my first jobs we had a hand held phase rotation checking unit that used 12 LED in a circle to show a real visual confirmation of rotation.

One day out of boredom and speculation as to how it worked we opened it up and found it used a bunch of divide by N IC's that basically brought the frequency of each phase down to where it was observable via the dozen RED LED's arranged in a clockface circle.

I think our speculation came down to it using 6 sets of divide by 100 frequency reducers to alternate two LED's per divider set of which I think half were arranged in a 'Wye' line sensing configuration and the other half 'Delta' so that as viewed as a clock face it looked like a half moon rotating one way or the other depending on how it was connected the lines.

Granted it was far more complex than other basic two or three lamp designs but it gave a near idiot proof visual representation of the rotation of the electrical phases.

Unfortunately at the time it didn't overcome the fact that between motor manufactures connecting ABC supply lines to 1,2,3 motor leads didn't always guarantee the same motor shaft rotation at the end so there was always a fair chance the motor would run backwards from the previous one anyway if brands were switched out despite having had a correct ABC to 123 line reconnect. Especially so on motors that had been taken apart that had their end bells and rotor swapped end to end to get the junction box onto the opposite side to line up with existing wiring and conduit layouts.

7. ### nsaspook AAC Fanatic!

Aug 27, 2009
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This! I've told our guys a thousand times to always pump test rebuilt pumps to be sure they turn in the correct direction. Trust No One.

8. ### tcmtech Well-Known Member

Nov 4, 2013
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But the little meter thingy said it should be going the right way so I didn't think I needed too!