I believe this is a polyurethane. Some PUs have a tendency to revert to 
lower molecular weights on exposure, especially prolonged, to high 
humidity at elevated temperatures. This depolymerisation may result in 
the PU softening and I could well imagine that the wire could "push" 
through the insulation if the Xfo is wound with a high wire tension, 
keeping it under stress.

Alternatively, remembering that the beauty of a PU insulation is that 
the insulation will retreat when the wire is dipped in molten solder. As 
your Xfo is a SMT device, it is obviously subjected to soldering 
temperatures during reflow. Is the body of the device protected from the 
reflow conditions by some form of insulation?

Hope this gives you a clue

Brian

On 31.10.2013 17:07, Ed Popielarski wrote:
> NEMA MW82-C Class 180 C

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________