Fault Current:

[ptonsparky]

Reply I received when I asked about fault current available:

Current 37.5 KVA Transformers

At 277V ? 5250A L-G

At 480V ? 3000A L-G


Uprate 100 KVA Transformers

At 277V ? 11900A 3 Phase L-G

At 480V ? 6850A 3 Phase L-G

It is a 277/480 Y. How does the 480v L-G work into this?

 

[lielec11]

Reply I received when I asked about fault current available:

Current 37.5 KVA Transformers

At 277V ? 5250A L-G

At 480V ? 3000A L-G


Uprate 100 KVA Transformers

At 277V ? 11900A 3 Phase L-G

At 480V ? 6850A 3 Phase L-G

It is a 277/480 Y. How does the 480v L-G work into this?

It is helpful to know the impedance (%Z) of each transformer. However, if you figure 5% just for this conversation you'll get the following:

37.5kVA / (.831 x .05) = 902.5AIC (3-phase). To get the L-G values you divide by 3. Not sure where 3000A is coming from, unless my math is off. Also, 480V is typically a phase-phase value, not phase to ground.

 

[ptonsparky]

It is helpful to know the impedance (%Z) of each transformer. However, if you figure 5% just for this conversation you'll get the following:

37.5kVA / (.831 x .05) = 902.5AIC (3-phase). To get the L-G values you divide by 3. Not sure where 3000A is coming from, unless my math is off. Also, 480V is typically a phase-phase value, not phase to ground.

That is my issue...480v L-G.

 

[lielec11]

That is my issue...480v L-G.

Theoretically any voltage can be obtain depending on the transformer windings, however, I'd ask for clarification from whoever gave you this information (utility?).

 

[ptonsparky]

Info came from POCO and after questioning the 480 L-G issue twice, they came back with a L-L value of 7900 which is more in line with my SEWAG.