If one normally davens nusach sefard but happens to daven with a nusach ashkenaz minyan, does one say keser in mussaf in keeping with one’s minhag or nekadesh with the minyan?
Answer:
You should say Kedusha as the Nusach of the Minyan in which you are davening.
Best wishes.
Sources:
Shut Meishiv Davar 1:17; Shut Iggros Moshe Orach Chaim 2:23.
Rav Moshe Feinstein explains that Kedusha is something that is said communally, so that the Nusach one uses should be the same as the congregation, even if one says it quietly.
Best wishes.
