112.5kVA transformer 480Vdelta primary - 208Y/120V secondary.
We used to put 175A/3P breaker in the panel that feeds this transfomer.
Square-D recently issues a document and states that we have to use 250A/3P breaker to protect this xfmr instead of 175A/3P, they said because 175A/3P won't help transformer inrush current. This doesn't make much sense to me:
1. Never heard a xfmr can have inrush current, most of time we won't have motor load fed out of this type of xfmr, typical load shall be receptacle and lighting or small equipment.
2. If we increase primary CB from 175A to 250A as recommended, we may need to increase primary wire size to comply with NEC.
3. We may run into coordination issue between 250A breaker and its upstream breaker instead of 175A CB.
4. Not sure if other manufacturers have similar approach?
Anyone has any experiences with this matter? Thanks!
We used to put 175A/3P breaker in the panel that feeds this transfomer.
Square-D recently issues a document and states that we have to use 250A/3P breaker to protect this xfmr instead of 175A/3P, they said because 175A/3P won't help transformer inrush current. This doesn't make much sense to me:
1. Never heard a xfmr can have inrush current, most of time we won't have motor load fed out of this type of xfmr, typical load shall be receptacle and lighting or small equipment.
2. If we increase primary CB from 175A to 250A as recommended, we may need to increase primary wire size to comply with NEC.
3. We may run into coordination issue between 250A breaker and its upstream breaker instead of 175A CB.
4. Not sure if other manufacturers have similar approach?
Anyone has any experiences with this matter? Thanks!