Phasing

[jonny1982]

Can anything bad happen if a transformer is wired with the phases in reverse?

For instance, take a 45KVA, 3 phase, 480 primary 208 secondary transformer. H1 is C phase, H2 is B phase, and H3 is A phase instead of H1 being A, and H3 being C.

Thanks

 

[augie47]

The transformer could not care less.

 

[jonny1982]

The transformer could not care less.

I guess the only thing to be concerned with with phase rotation is motors, and they are usually bump tested upon startup anway, correct?

 

[ActionDave]

I guess the only thing to be concerned with with phase rotation is motors, and they are usually bump tested upon startup anway, correct?

That all depends. New installs, yes.
Is this real life or a thought exercise under discussion?

 

[Smart $]

That all depends. New installs, yes.
...

At least one motor should be decoupled, bumped, and rotation verified when a transformer is replaced.

 

[electricalist]

I have been to a few calls where someone changed out a panel and guess what. My ac doesnt work.

 

[cadpoint]

... H1 is C phase, H2 is B phase, and H3 is A phase.

You could probably go down the street and find out what exactly
is on the power pole.
I've got a picture that shows exactly that!

Image a two sets of letters in a slight triangle of letters Z, X, Y respectfully over A,C,B.

Games on, tired of playing with photo-bucket!

 

[ActionDave]

At least one motor should be decoupled, bumped, and rotation verified when a transformer is replaced.

Agree.

 

[Carultch]

Can anything bad happen if a transformer is wired with the phases in reverse?

For instance, take a 45KVA, 3 phase, 480 primary 208 secondary transformer. H1 is C phase, H2 is B phase, and H3 is A phase instead of H1 being A, and H3 being C.

Thanks

The transformer will work the same, no matter what sequence the phases are connected.

Where it does matter, is at loads that are connected. Specifically motor loads. The sequence of the phases will set the direction of the motor rotation.

If anything is done upstream a load that requires proper phase rotation, it should be disconnected, and the phase rotation should be checked, before it is operated again. If the phase rotation is wrong, you can swap any two phases and it will be correct.

 

[GoldDigger]

I would think that a common core three phase transformer would not be affected by the direction of phase rotation but would be seriously affected by one winding being connected in reverse polarity compared to the other two.

 

[iwire]

I would think that a common core three phase transformer would not be affected by the direction of phase rotation but would be seriously affected by one winding being connected in reverse polarity compared to the other two.

Makes sense but would be a manufacturing mistake not a installer mistake.