1.1 Transformers Covered This recommended practice covers general recommendations for the application, installation, operation and maintenance of single and polyphase dry-type general purpose, distribution, power, and auto-transformers of the following types: 1) Ventilated, indoor and outdoor, self-cooled cooled or forced air cooled 2) Nonventilated, indoor and outdoor, self-cooled or forced air cooled 3) Sealed, indoor and outdoor, self-cooled 1.2 Transformers Not Covered This recommended practice does not apply to the following: 1) Instrument transformers 2) Step voltage and induction voltage regulators 3) Arc furnace transformers 4) Rectifier transformers 5) Specialty transformers NOTE -- Both ventilated and nonventilated transformers may be furnished with windings utilizing materials such as solid insulating material which allow or require different practices from those required in this recommended practice. In such equipment the recommendations in this recommended practice may be modified by specific manufacturer's recommendations.