Dry-type transformers are most commonly used where the incoming electric service is at 480 Volts. Service at 120 Volts is a common supply voltage for small appliances and business machines. If 120-Volt lighting is served by the same transformer, that must be considered in any comparison. Panel boards for 277 Volt lighting are more expensive per branch circuit but fewer branch circuits might be needed with the higher voltage. However, practical considerations of areas of control may reduce this advantage. Therefore, it is necessary to look at each situation carefully when considering the panel board and the dry-type transformer size.
This graph shows relative costs of adding the transformer on the 480 Volt system.
