I have a question. In our industry we work a lot with dry type transformers with a 480V primary and a 208 or 240V secondary. Typically these transformers are under 125kVA. When I run calcs, typically the secondary side has a higher hazard than the primary. So my questions are:

1) Do you typically apply a label to the transformer?

2) If yes to #1, does the label represent the primary or secondary side hazard, even though the secondary is 240V or less?

Think about how a small transformer is built, the terminals are effectively: LV-HV-LV-HV-LV-HV-LV. It is almost impossible to have a L-L fault on the secondary that does not create a L-L fault on the primary.

However, when a customer requires a label on a transformer we will use the worst case AFIE and the highest voltage, irrespective of if it is on the primary or secondary.

Thanks for the replay, so is it industry standard to place a lablel on the transformer?

Perhaps I have something set wrong with in my EasyPower, but typically the higher voltage has a lower AFIE, so when you say worst case and highest voltage are you refereing to two lables (typically the 480V side is Class 0 and the secondary side comes up as Class 1 or 2)

If it is 208 volt and under 125 kVA, then it falls under Exception No. 1 to 130.3 and analysis is not required for the secondary. If the primary is higher than 1.2 cal/cm² then it needs a label more than Cat 0.

Your program is probably providing correct results. It is extremely unlikely that a secondary fault will cause the primary devices to operate very fast, resulting in a very long clearing time.

We use a single custom label, listing the highest voltage (in most cases the primary) and the highest PPE category (in most cases on the secondary). In general, I am not a believer in multiple labels on a single device.