Maximum Amps on a 25kVA transformer

[stanward]

If a dedicated 25kVA transformer feeds a residential home at 120/240V, what is the max ampacity available to that residence?

Is it 25kVA/120 or is it 25kVA/240?

Thanks,

Stan

 

[charlie b]

You divide by 240. Welcome to the forum.

 

[stanward]

Thank you Charlie!

 

[Bugman1400]

careful.....distribution type xfmrs can typically supply 200% of their rating and PoCos know and use this. So, in the Summer peak, if the load is calc'd to be higher than 25kVA for a few hours during the day, the PoCo will not change to a higher rated xfmr. So, your 25kva xfmr may be supply current that is significantly more than the rated ~104 amps.

 

[zog]

If a dedicated 25kVA transformer feeds a residential home at 120/240V, what is the max ampacity available to that residence?

Is it 25kVA/120 or is it 25kVA/240?

Thanks,

Stan

Are you asking for max fault current?

 

[Bugman1400]

Are you asking for max fault current?

That's a good question. What is the typical impedance Z% for distribution type xfmrs?

 

[zog]

That's a good question. What is the typical impedance Z% for distribution type xfmrs?

Not sure, I never deal with ones this small, maybe 8%ish?

 

[Iron_Ben]

That's a good question. What is the typical impedance Z% for distribution type xfmrs?

I've seen nameplate values from 1.6% to 2.1%. Sample size maybe 30 or 40 transformers, 15 to 75 kva perhaps. I always used 1.8% when doing sc calculations. The size and length of the service will often have a very significant impact on available fault current levels, more than one might intuitively think.