- Location
- Connecticut
- Occupation
- Engineer
You can if it doesn't already have a secondary OCPD. So on a D-D you can choose, but a D-Y already HAS a secondary - the choice was made for you.
Where are you reading anything in Article 450 about D-D or D-Y? It doesn't exist. The Protection required by Table 450.3(B) has NOTHING to do with whether a transformer is D-D or D-Y. The Table applies the same to both types of Transformers. There is nothing in the text that tells you to apply one Protection Method to one type of transformer or the other. You are injecting that requirement yourself.
You design the system first and set sizes second. On a D-D you can elect to add or omit a secondary THEN you look up the appropriate row to select values. On a D-Y it's already been forced on you. You can't omit or ignore it just because you want to use the first row.
You CANNOT elect to omit a secondary OCPD on a D-D transformer if the Primary OCPD is greater than 125% (or next size up.)
This is the fallacy in your argument. You are trying to assign "Primary Only" or "Primary & Secondary" protection of a transformer based on whether the secondary conductors can be protected by the Primary OCPD or whether they need to be protected by an OCPD on the secondary size.