Q. What are the disconnecting requirements for a transformer?
A. A disconnect is required to disconnect all transformer ungrounded primary conductors. The disconnect must be located within sight of the transformer, unless the location of the disconnect is field-marked on the transformer and the disconnect is lockable [450.14], as shown in the Figure. This new Code requirement applies to transformers of any voltage, except Class 2 or Class 3 transformers.
Note: Within sight means that it's visible and not more than 50 ft from one to the other [Art. 100].