Re: Dry types on the roof
Please let me know if this information has been helpful as researchin my archives does take some time.
The Dry type distribution transformer that I had worked for as an application engineer didn't have a specific NEMA 3R design, in other words there was no special design for MEMA 3R.
If it wasn't and encapsulated design the only other choice was ventilated.
The ventilated design had a weathershield kit available that, when properly installed, provided a NEMA 3R rating. It protected the openings against rain but allowed for proper ventilation.
Keep in mind that in order to get a NEMA 3R rating the transformer with this modification had to pass testing which required to pass the NEMA 3R requirements.
However, my notes indicate that we did not recommend this design in a snowy climate as there would be adequate protection against rain but there was concern for wind blown snow entering the enclosure even though it technically met NEMA 3R requirements.
Also, most, if not all, of the manufacturers use an electrostatic powder coating technique which is baked on as a finishing technique. My reference, which is from 1995, shows that the finish was polyester at the time that provided 100% coverage at no less that 1.3mils. Along with the many test was that it must have the capability of meeting a 600 hour salt spray requirement.
Also, as I recall, because if the great advances in the robust nature of these powder coats, there was no difference between the techniques used in either indoor or outdoor gear.
Of course if the finish was to be penetrated such as an abrasion, it would expose the carbon steel which is prone to rust. I believe there was an option available for stainless steel and possibly aluminum. However, as with any manufacturer the cost goes through the roof when specifying a special, off the production line, design.
