Hi I would like to know where in the NEC talks about using liquidtight conduit to connect a dry type transformer because fo vibration. Thank you

Welcome to the forum victor.

You will not find anything in the NEC requiring liquidtight conduit to be used to connect a dry type transformer because of vibration.

It is just a design choice buy the installer.

I'll go a bit farther...

True, the NEC does not address the matter. However, NECA standards document the use of flex at transformers as "trade practice", or good workmanship.

That aside, I noticed recently that some transformers have internal rubber mounts, so the piping actually does not connect to the part that vibrates.

I still like to see flex at the case, though. Old habits die hard.

hi thank you for your reply, where can I get a copy of NECA stating the use of liquid flex as a good workmanship. Thank you