Comparative performance of open and totally enclosed machines

Continuous improvements in insulating materials, manufacturing consistencies in sealed windings and extensive laboratory testing of various systems show that synchronous machines with NEMA II construction can replace totally enclosed machines. Tests on windings in corrosive atmospheres show that sealed insulation systems are impervious to the environment. Standard maintenance ensures that incendive arcing will not be generated in potentially hazardous environments. When compared to totally enclosed machines, the NEMA II-type construction is lighter, more efficient, has lower short-circuit current and associated torques and is easier to maintain.