IEEE 1584 125 kVA transformer “Exception�

The conversation about the 125 kVA transformer “exception� comes up regularly and has surfaced not only at the Arc Flash Forum but in other recent conversations and e-mails that I have had. This is also a major topic of discussion during the revision process for the next edition of IEEE 1584.

The exact language from IEEE 1584-2002 is:

4.2 Step 1
“Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low impedance transformer in its immediate power supply.�

It has been almost 16 years since this standard was published (September 2002) and years since I have asked this question. Thoughts and practices have evolved along the way so here is this week’s question.

Do you/clients/consultants use the 125 kVA exception from IEEE 1584?
-Yes
-We use a variation (please explain)
-No
-Does not apply

We have in the past ignored these "low powered" panels, as I call them. The problem is the qualified persons still need some sort of PPE to open the equipment up and a generic "Arc Flash Hazard Present" does little for our electrician friends. Recently I have been adopting the NESC approach from Table 410-1, especially knowing that the new 1584 is addressing the issue but not completely. With the NESC approach I can not put a label/PPE on the "low powered" equipment.