Transformer Primary Current

[jody.boehs]

I have a 15kVA 480/240 - 240/120 single phase transformer on which I need to figure out what the inrush current will be. Of course, the usual calculation is 15,000 / 480 = 31.25A. This particular transformer does not give me any type of service factor rating to apply to this calculation. Is there just a 'rule of thumb' that I should follow with this? Like 125% or 150%???? Because there's no way a 32A breaker, or even a 35A, will handle this load.......Basically, how should I figure this so I can get the right breaker?

 

[jody.boehs]

I have a 15kVA 480/240 - 240/120 single phase transformer on which I need to figure out what the inrush current will be. Of course, the usual calculation is 15,000 / 480 = 31.25A. This particular transformer does not give me any type of service factor rating to apply to this calculation. Is there just a 'rule of thumb' that I should follow with this? Like 125% or 150%???? Because there's no way a 32A breaker, or even a 35A, will handle this load.......Basically, how should I figure this so I can get the right breaker?

I was just looking at Article 450.4 and it tells me 125%. Is this the right Article and rating?

 

[jumper]

125% is for when you have primary protection only. I have never wired one this way.

If you have primary and secondary protection, primary could be 250% and secondary 125%.

There is also a "Note 3" in that table when you have both, but I could not explain it. I leave stuff like it to an EE.

Edit:

Simple way to wire tranny: