Single phase from 3 phase AFC calc

[electrofelon]

Having a senior moment here. If I have a three phase transformer feeding a 120/208 single phase service, is the AFC calc just transformer three phase FLC / impedance?

 

[electrofelon]

Having a senior moment here. If I have a three phase transformer feeding a 120/208 single phase service, is the AFC calc just transformer three phase FLC / impedance?

Isn't this an easy one?

 

[NewtonLaw]

Assuming AFC is Arc-Fault Calculation, yes the short Circuit duty at the point of the fault would be the FLC (assuming this is the base current used in the per unit calculation) divided by the per unit impedance. If you are speaking of just the transformer, then the FLC/(%Z of the transformer/100) = Isc

Hope this helps.

 

[electrofelon]

Assuming AFC is Arc-Fault Calculation, yes the short Circuit duty at the point of the fault would be the FLC (assuming this is the base current used in the per unit calculation) divided by the per unit impedance. If you are speaking of just the transformer, then the FLC/(%Z of the transformer/100) = Isc

Hope this helps.

Thank you. So no caveats being it is a three phase transformer with only two legs brought out? Only thing I can think of is that L-N fault will NOT be potentially 1.5 times higher than L-L like it typically is for single phase transformers.