# 3 phase xfmr



## ABofAT (Dec 5, 2014)

Going from a 3 phase transformer to a switchgear, normally one would hook up A phase to A phase, B to B, and C to C. Is it a problem if one hooks it up A to B, B to A, and C to C?


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## pete87 (Oct 22, 2012)

ABofAT said:


> Going from a 3 phase transformer to a switchgear, normally one would hook up A phase to A phase, B to B, and C to C. Is it a problem if one hooks it up A to B, B to A, and C to C?





Transformer will be CROSS EYED !

Is there a high leg ?




Pete


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## The_Modifier (Oct 24, 2009)

If there are motors connected to the panel, you may be doing a lot of walking to check the rotation of them all.


P.S. finish filling out your profile. please.


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## Big John (May 23, 2010)

ABofAT said:


> ...Is it a problem if one hooks it up A to B, B to A, and C to C?


 If your loads are rotation dependent, it darn sure can be.


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## glen1971 (Oct 10, 2012)

The_Modifier said:


> If there are motors connected to the panel, you may be doing a lot of walking to check the rotation of them all.
> 
> 
> P.S. finish filling out your profile. please.


A lot of walking?? Why? If it's a new installation, all the motors will have to be checked anyway.. If it is an upgrade, check one motor.. If it's wrong, they all will be...

To the OP.. If it's a new construction, why would you do it this way? I've done it this way as an upgrade, but that was to keep the existing rotation correct...


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## MXer774 (Sep 1, 2014)

Ditto to da Glen except the statement of if one motor is reversed, then all will be. I have had different motors throughout the facility that didn't all agree to the same phase orientation. Now if the motors were the same, then the equipment would accept it.


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## RIVETER (Sep 26, 2009)

ABofAT said:


> Going from a 3 phase transformer to a switchgear, normally one would hook up A phase to A phase, B to B, and C to C. Is it a problem if one hooks it up A to B, B to A, and C to C?


I've never used a "Phaser" device but I hear they are out there for use in these instances.


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## micromind (Aug 11, 2007)

It'll work, but unless there's a valid reason, it's absolute hack.


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## glen1971 (Oct 10, 2012)

MXer774 said:


> Ditto to da Glen except the statement of if one motor is reversed, then all will be. I have had different motors throughout the facility that didn't all agree to the same phase orientation. Now if the motors were the same, then the equipment would accept it.


If you are doing an upgrade to a transformer, such as replacing due to a failure, and the existing rotation was unknown, and once done you check one motor fed from the new transformer and it's rotation is wrong, how would any others be correct? Providing that other motors checked are fed from the system powered by the replaced transformer the rotation would be the same for all the gear.. I'm not saying that they are all cw or all ccw.. Just that they are rotating the way that they were before the upgrade/replacement..

Unless I'm missing something...


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## MXer774 (Sep 1, 2014)

My bad. I was referencing to new inatallation on new facility on initial startup. I agree with you on the replacement scenario.


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## power (Feb 27, 2012)

If you _*must*_ swap two phases (perhaps due to conductor length) on the primary, then intentionally swap two on the secondary. Same is true visa-versa. Problem solved.


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## Big John (May 23, 2010)

power said:


> If you _*must*_ swap two phases (perhaps due to conductor length) on the primary, then intentionally swap two on the secondary. Same is true visa-versa. Problem solved.


 I don't understand. What's the value of that?


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## power (Feb 27, 2012)

ABofAT's original questions was:
"Going from a 3 phase transformer to a switchgear, normally one would hook up A phase to A phase, B to B, and C to C. Is it a problem if one hooks it up A to B, B to A, and C to C?"

I am assuming that he wouldn't intentionally swap the primary phases A and B unless he was forced to. Perhaps his primary conductors are too short to reach the lugs on his new transformer, and that making such a swap would remedy the situation. 

But in doing this, all upstream 3-phase motors are now going to operate in the opposite direction. So, I suggested intentionally swapping two of the secondary phases.....any two will work. This way, it's a figurative "double reverse" which will revert all 3-phase motors back to their original rotation.


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## don_resqcapt19 (Jul 18, 2010)

408.3 (E ) Bus Arrangement. (1 ) AC Phase Arrangement. 
Alternating-current phase arrangement on 3-phase buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard, switchgear, or panelboard. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked.


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## 360max (Jun 10, 2011)




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