Transformer dedicated working clearances

zam

Member
Location
New York, NY
Do transformers have dedicated working clearances like electrical panels and other switch-gear? The required clearances (for ventilation purposes) of a transformer are specified by the manufacturer. Can a transformer be installed in a dedicated 1-hour fire rated room with 1-foot of space behind the transformer and 1-foot of space on the left side and 1-foot on the right side and 3-feet in the front. This transformer will have a rating of greater than 112.5 kVA. A lot of times architects and the interior designers just don't want to spare any room for electrical equipment. Thank you.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
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.
 
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?
 
Top