Does the working space in Article 110.26 apply to transformers? Would a 480V panelboard across the isle from a 480 to 208 transformer require 4' between them? Also, do the working space requirements apply to the sides of the transformer? If not, how much space would required on the sides to run conduit in and pull wire (aren't transformers usually fed with a LB into to side?) I am laying out an electrical room, but I'm not an electrician, and I'm not sure how the connections to transformers are usually made.

Finally, can the transformer be backed right up aginst a wall, or does it need breathing room behind it?

99NEC 450-9. Transformers with ventilating openings shall be installed so that the ventilating openings are not blocked by walls or other obstructions. The required clearances shall be clearly marked on the transformer.

110-16 working clearances would not be modified by ventilation clearances.

Working clearances are required to perform preventative maintenance on the xfmr. Granted that most PM can be done with the xfmr not energized, but some will be done live (such as infrared measurements). You will need at least condition 2, possibly condition 3 depending on the interpretation of the AHJ.

[This message has been edited by Ron (edited 07-26-2003).]