. Question: Is it permitted to grate potatoes on Yom Tov with a grater?
Answer: Regarding grating on Yom Tov, the Shulchan Aruch (Orach Chayim Siman 504 Se’if 1) writes that spices may be crushed in the regular way, because if they would be crushed prior to Yom Tov they will lose [some of] their taste.
However, salt may only be crushed on Yom Tov with a shinuy (i.e., in an unusual manner) because since salt could have been crushed prior to Yom Tov without losing its flavour, there is no dispensation to crush it on Yom Tov without a shinuy.
It is clear from the Poskim (c.f. Mishna Berura s.k. 2, s.k. 11) that the allowance to crush spices applies to vegetables as well – provided that the vegetables would somewhat spoil if grated prior to Yom Tov.
Returning to potatoes, it is clear that if one wishes to cook with grated potatoes on Yom Tov, these will spoil (to some extent) if grated prior to Yom Tov, therefore they can be grated on Yom Tov, even with a grater, and there is no necessity to grate with a shinuy (c.f. Shmiras Shabbos Kehilchoso Perek 7 Se’if 2).