calculate aic

[RoberteFuhr]

If you are doing an SC and a AF study, just make sure that you request the Maximum (for the SC study) and the minimum (for AF Study) values of fault current. Sometimes the worst case for AF energies is the lower fault current which causes the devices to take longer to trip.

 

[zog]

No.

The label is intended to reflect only amps from the utility. There is not even a requirement for X/R ratio.
Several utilities already provide this information in their service manuals.

From Xcel Energies (my emphaisis):

Tables IA through V in this Section show the available RMS symmetrical fault currents that may be expected at the
secondary terminals of distribution transformers. Each fault current value listed in the tables is based on the lowest
percent impedance transformer that might be set initially or as a replacement. No primary source or secondary line​

impedance has been included since it is generally relatively small, may change, and cannot be accurately forecasted.

So this fault current on the label won't include any motor contributions huh? Hmmmmm.

 

[jim dungar]

So this fault current on the label won't include any motor contributions huh? Hmmmmm.

In reality, any motor contribution should be relatively minor, remember industrial services are exempt from this NEC requirement.

This label is to be used only to choose the AIC ratings of protective devices and the SCCR of equipment at the service entrance.

For decades UL has required service entrance equipment to have a short circuit current rating, however there has never been a requirement for any 'field' value to compare it to.

Maybe the next step is to make the label somewhat meaningful, by requiring its values be adjusted to be directly usable with the UL AIC ratings for devices installed.

 

[JWCELECTRIC]

Could the infinity Z% plus the contributed motor load be used to find the maximum AIC if the KVA size of the utility transformer is known at worst case?

 

[jim dungar]

Could the infinity Z% plus the contributed motor load be used to find the maximum AIC if the KVA size of the utility transformer is known at worst case?

If you are using an infinite bus calculation what purpose is there in adding additional current, is it so you now have more than infinity?