# Abc=bca=cab



## chicken steve (Mar 22, 2011)

you _already_ typed it Travis

oh and, this immediately popped to mind>>>>
:whistling2:




:no:
~CS~


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## glen1971 (Oct 10, 2012)

I had a consultant argue with me when we checked rotation before a transformer swap and found it to be cba.. So I had my guys land the wiring Blue, Black, Red (CBA up here), realizing it was still a 50-50 shot of getting it right.. Well low and behold it was backwards.. I said no biggie, get the utility to drop the fuses and we'll make it Red, Black, Blue.. The consultant comes back and says "That's why the rotation is wrong. You can't switch rotation with "A" and "C", only "A" and "B" or "B" and "C"...":blink::blink: "What??" was my reply to that.. 
I had the electrical testing tech (who was agreeing with the consultant) write it out like Travis has.. And told them to switch, AB, then BC and finally AC.. He said yeah it works on paper but not electrically... Wow..... They left and the facility electrician, who had been there the whole time, says "Wow... You know you're right, right?"... I said "Yup.. And how does it make you feel knowing those 2 clowns are going to tell you that I'm done my work and your plant is ready to run?".....
It takes all kinds.. lol...


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## micromind (Aug 11, 2007)

Yes, the rotation will be the same. 

Occasionally, especially with high-strung 3Ø motors, better current balance can be achieved by 'rolling' the phases. This means moving A to where B was, B to where C was and C to where A was. 

The net result is that rotation is the same but current balance has either improved or gotten worse. 

HVAC compressors and submersible pump motors will respond best though all motors can benefit.


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## Cow (Jan 16, 2008)

micromind said:


> Yes, the rotation will be the same.
> 
> Occasionally, especially with high-strung 3Ø motors, better current balance can be achieved by 'rolling' the phases. This means moving A to where B was, B to where C was and C to where A was.
> 
> ...


Coincidentally, I just went through this yesterday with a guy. We're doing a shutdown on Monday and we noticed one of the panels has an empty single pole space on each side of the panel in the middle, only leaving a 2 pole space on each side at the bottom of the panel. Seeing as we need room for some 3 pole breakers, I asked him "can I just move all these breakers up one space to make room for a 3 pole, or will it swap rotation?"

It's interesting watching the gears start turning while they think about it. It all made sense to him though when we pulled out the rotation tester and moved it around in the panel.


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## Big John (May 23, 2010)

Is there such a thing as absolute phase rotation?

I have always been under the impression that you must use the same rotation meter for both before and after checks, because there is no way to determine if each meter reads RST the same direction.

That is to say, two different meters may read the same circuit CCW and CW, respectively.


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## JohnDeere (Nov 10, 2015)

Big John said:


> Is there such a thing as absolute phase rotation?
> 
> I have always been under the impression that you must use the same rotation meter for both before and after checks, because there is no way to determine if each meter reads RST the same direction.
> 
> That is to say, two different meters may read the same circuit CCW and CW, respectively.



I've wondered that myself. I always used to see gensets that are rotation labeled according to RST and I was always thinking "yeah, so" and then checked with my own


Sent from my iPad using Tapatalk


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## emtnut (Mar 1, 2015)

chicken steve said:


> you _already_ typed it Travis
> 
> oh and, this immediately popped to mind>>>>
> :whistling2:
> ...


Thanks for the laugh :thumbup: Pretty much sums it up


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## don_resqcapt19 (Jul 18, 2010)

Big John said:


> Is there such a thing as absolute phase rotation?
> 
> I have always been under the impression that you must use the same rotation meter for both before and after checks, because there is no way to determine if each meter reads RST the same direction.
> 
> That is to say, two different meters may read the same circuit CCW and CW, respectively.


I always thought they were absolute as far as rotation. Some even us a mini-motor so I don't see why they can't be absolute. 

However they can't tell one phase from another so you can only use them when you only need rotation. You can't use them for applications where you are going to connect two sources in parallel.


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## JRaef (Mar 23, 2009)

It's only relevant as a relationship. There is no absolute as to which phase is A, B or S, or R, S, or T, or U, V, or W. Those are just conventions we use to describe it. If your utility gives you CBA, as it is here in Northern California, you live with it. Makes absolutely no difference for permanently installed equipment because once you check rotation, it's fixed and nothing changes.

Where it DOES get people in trouble is if you bring in a piece of equipment from somewhere else, and the person who dismantled it ASSumes that marking the colors was all that was needed for hooking it up at the other end. If the rotation is different, the color coding means nothing any more. That's why we test on a new installation, EVERY time.

The only other time I have been messed up was with some specific brands of phase monitor relays. There are a few, not many, that MUST see the rotation as A-B-C. For those, the rotation must be corrected at the line side BEFORE you check rotation on the load side. It can be a nasty little gotcha if you don't know.


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## KennyW (Aug 31, 2013)

Big John said:


> Is there such a thing as absolute phase rotation?
> 
> I have always been under the impression that you must use the same rotation meter for both before and after checks, because there is no way to determine if each meter reads RST the same direction.
> 
> That is to say, two different meters may read the same circuit CCW and CW, respectively.


I dont get it- the meter should be labelled what direction equals ABC. If not its useless. You are trying to determine phase sequence, the direction is just a means of indicating the sequence. CW or CCW is irrelevant really as long as the meter says which is 1-2-3. 1-2-3 is universal. 

I use a digital phase rotation function on my meter and it reports the actual phase sequence. "Direction" is just a side effect. Really what you care about is phase sequence. 

ABC, BCA, and CAB all result in a 1-2-3 phase sequence. 

So yes it is absolute. In the time domain, the waveforms follow each other.


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## micromind (Aug 11, 2007)

Every phase rotation meter I have ever seen will give CW or Forward or Correct or something like that when the sequence is ABC. 

Every phase failure relay I've seen wants to see ABC as well. 

Years ago I had to troubleshoot a DC drive that wouldn't work. I can't remember if it was 240 or 480 and it was around 20HP. Odd as it may seem for a drive that was DC output, the incoming phase rotation needed to be ABC. 

I've also worked with a few 25 (synch check) relays that needed to be ABC.


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## chicken steve (Mar 22, 2011)

~C:jester:S~


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## bobbarker (Aug 6, 2015)

I pictured the name of this thread being sung by the Jackson 5:laughing:


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## chicken steve (Mar 22, 2011)

bobbarker said:


> I pictured the name of this thread being song by the Jackson 5:laughing:






~C:jester:S~


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## Gnome (Dec 25, 2013)

Cow said:


> Coincidentally, I just went through this yesterday with a guy. We're doing a shutdown on Monday and we noticed one of the panels has an empty single pole space on each side of the panel in the middle, only leaving a 2 pole space on each side at the bottom of the panel. Seeing as we need room for some 3 pole breakers, I asked him "can I just move all these breakers up one space to make room for a 3 pole, or will it swap rotation?"
> 
> It's interesting watching the gears start turning while they think about it. It all made sense to him though when we pulled out the rotation tester and moved it around in the panel.


That is a great apprentice learning question.


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