What size breaker do I need for a 150kva
- Thread starter mdgon
- Start date
- Status
barbeer
Senior Member
- Location
- Pinellas County, FL
What does the load calc tell you?
barbeer
Senior Member
- Location
- Pinellas County, FL
I would test your equipment, sounds like a fault to me.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
What you have is a trip on in-rush current. I would venture to guess you have a 600A breaker on the 208V side, and a 225A breaker on the 480V side. Using a standard damage curve and showing inrush current, both breakers are going to trip on inrush. Which one, is a race, but I'll bet it's the breaker on the 480V side.
You need to get the manufacturers damage curve for the transformer, and inrush multiplier. Then select the protection such that it will not trip on inrush but also protects the transformer from damage. I would investigate using a 500A breaker on the 208V side, that has an adjustable instantaneous trip to get you out beyond the inrush. On the 480V side you are probably going to have to resort to time delay fuses.
I am not surprised by this since IMO the NEC charts work poorly for properly selecting protection of transformers.
You need to get the manufacturers damage curve for the transformer, and inrush multiplier. Then select the protection such that it will not trip on inrush but also protects the transformer from damage. I would investigate using a 500A breaker on the 208V side, that has an adjustable instantaneous trip to get you out beyond the inrush. On the 480V side you are probably going to have to resort to time delay fuses.
I am not surprised by this since IMO the NEC charts work poorly for properly selecting protection of transformers.
inrush
inrush
I missed any reference to what size breaker you actaully are using. As mentioned by kingpb, I would think 600 amp would be the commonly used breaker in this situation. To add a bit to his post, check the breaker you have and see if has adjustable trip settings. You might simply need to make an adjustment.
inrush
I missed any reference to what size breaker you actaully are using. As mentioned by kingpb, I would think 600 amp would be the commonly used breaker in this situation. To add a bit to his post, check the breaker you have and see if has adjustable trip settings. You might simply need to make an adjustment.
frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
either 500 or 600 amp primary breaker [ 208 v side ] will work but only one curpit as other mention is inrush current IMO with step up transformer it will take more inrush current than downstep transforemer due the design of it.
Beside dont be suprised with the amount of inrush current it can be anywhere from 5 to 8 X of FLA current some case higher but i doubt but it do show up like that once a while.
Merci, Marc
Beside dont be suprised with the amount of inrush current it can be anywhere from 5 to 8 X of FLA current some case higher but i doubt but it do show up like that once a while.
Merci, Marc
:grin: - Status