Parallel transformers operation and NEC

[Mila15]

NEC permits using transformers in parallel operation and switching as one unit. Is switching as one unit a mandatory? Does that mean I have to use a 6 pole switching application, or I don't have to do that if proper tagout procedure is used? This is for 480v, 300KVA XFMRs application. Does anyone have any experience with that?

 

[7anoter4]

This is what NEC says:
450.7 Parallel Operation. Transformers shall be permitted to be operated in parallel and switched as a unit, provided the overcurrent protection for each transformer meets the requirements of 450.3(A) for primary and secondary protective devices over 1000 volts, or 450.3(B) for primary and secondary protective devices 1000 volts or less.
In my opinion, you are not required to disconnect both transformers at the same time, but if you want to do so you have to comply with this article.

 

[Mila15]

This is my interpretation as well, but some say the AND between "operated in parallel" and "switched as a unit" means they must go together! No one knows what NEC intends in most cases! I think they worry about danger of back feeding if only one transformer is turned off, but proper switching should take care of that.