Side and rear spacing is specified by the transformer manufacturer not the NEC. Working space in front is typically the dimension from 110.26 based on voltage but some have argued that the transformer will be worked on when it's de-energized so 110.26 does not apply.
Bumping this post back to life as I think there's a few nuances that would be good to discuss.
In the case of Low Voltage dry-type distribution transformers, I think you're correct, in that nobody will be working on the primary side or the secondary side while the transformer is energized. Any SOP that allows transformer work while energized is inviting a whole host of OSHA lawsuits. Would it be good design practice to include a courtesy working space in front of the transformer for maintenance work?
I would like to direct the question towards service transformers. In my example, a typical pad mount oil filled service transformer has both of its primary and secondary connections facing the front. When authorized personnel needs to access either compartment for maintenance or other operations, you would open the door and gain access to the respective conductors, bushings, and other items. In that instance, you'd have to abide by 110.34(A) and set the minimum working clearances according to the primary voltage and the particular condition. Is that the correct application of
the code and does anybody have other nuances they would like to share or expand upon?
