No, polymorphing someone does not make their armor stop working. Size is not a factor in that. If you polymorph your friend into a large creature while their armor is on the other side of the room, they wouldn't be able to put it on, though.
Equipment
If the polymorph form granted by a spell is of the same creature type as the target’s true form, the armor, weapons, and other equipment the target had at the time of casting remain visible and accessible and are changed by the magic to be usable in the new form. If any item is out of the target’s possession for more than 1 round, it reverts to its normal form. If the polymorph form is of a different creature type than the target’s true form, the spell causes the target’s armor (including any armor upgrades and the abilities of powered armor) to continue to function and be able to be activated by the target regardless of the character’s form. However, the armor isn’t visible in polymorph form, and it can’t be targeted or accessed (such as to change batteries) by either the target or other creatures. All other equipment is unavailable in a polymorph form of a different type and cannot be used, activated, targeted, or modified by either the target or other creatures.
TLDR: Nope. the armor either merges with them and keeps working if you turn them into something weird or expands along with them if you turn them into something that usually wears armor.
So I can still use weapons and armor upgrades installed on the armor, even though I'm polymorphed into a fish? I can still hit someone using the armor's damage rating?
I'm gearing up to play a powered armor wearing xenodruid with polymorph, so this will DEFINITELY be coming up in the near future.
I'm imagining a tiny bird headbutting someone for a lot of damage, or shooting lasers from its eyes. lol!
I think power armor is a whole other category and probably isn’t meant to transform at all. It’s sort of like a vehicle that you wear rather than gear.
What happens if you cast Polymorph 1 to transform a humanoid wearing gargantuan armor into a small animal? I think he becomes a small animal inside gargantuan power armor that he can no longer operate, and the same applies to any other transformation that doesn’t leave your size and subtype unchanged. Trying to make someone inside power armor bigger should just fail.
I think power armor is a whole other category and probably isn’t meant to transform at all. It’s sort of like a vehicle that you wear rather than gear.
What happens if you cast Polymorph 1 to transform a humanoid wearing gargantuan armor into a small animal? I think he becomes a small animal inside gargantuan power armor that he can no longer operate, and the same applies to any other transformation that doesn’t leave your size and subtype unchanged. Trying to make someone inside power armor bigger should just fail.
I thought that too at first, but when I delved into the official rules database, I found otherwise.
If the polymorph form granted by a spell is of the same creature type as the target’s true form, the armor, weapons, and other equipment the target had at the time of casting remain visible and accessible and are changed by the magic to be usable in the new form. If any item is out of the target’s possession for more than 1 round, it reverts to its normal form.If the polymorph form is of a different creature type than the target’s true form, the spell causes the target’s armor (including any armor upgrades and the abilities of powered armor) to continue to function and be able to be activated by the target regardless of the character’s form. However, the armor isn’t visible in polymorph form, and it can’t be targeted or accessed (such as to change batteries) by either the target or other creatures. All other equipment is unavailable in a polymorph form of a different type and cannot be used, activated, targeted, or modified by either the target or other creatures.
It seems pretty clear to me that polymorph affects even powered armor. What I'm uncertain of, is whether or not mounted weapons need to be "accessed" to be used, or if its considered part of the armor's normal abilities and can be used. I'm also wondering if, despite being installed in the armor, if mounted weapons count as equipment of a different type and thus "cannot be used, activated, targeted, or modified."
If powered armor can be transformed and still function I wonder if the speed limitations still hold.