On my main settlement I want to arm the main entrance with settlers in Power armour with heavy guns. Do I have to provide them with ammunition? I'm sure they don't need to be supplied with regular ammo for what they carry normally and I'm not sure if the fusion cores will deplete. Has anyone tried this?

not sure about ammo, but I don't think they will deplete the fusion cores. That is based on the assumption that settlers are similar to companions in how they treat resources like fusion cores when wearing power armor. I've had nick in PA for a bit now and he's not run out of juice yet.

I like to provide my settlers with armor & high ranking guns plus ammo just in case as I wasn't sure how the system worked. But by default they all carry pipe weapons which i like to replace with chain guns/lasers etc,

So long as you add a little ammo it should be fine. This infinite ammo exploit was something that was meant to be fixed in fo4 but from my experience so far it is only fixed for hostiles. A raider with a missile launcher with 2 missiles will run out of ammo and charge at you with melee.

This only seems to be ammo related. If they have grenades they seem to have an infinite amount of them. Grenades aren't treated as ammo.

Settlers I've given 20 units of ammo to still seem to have 20 units even after a fight.

You can put settlers into power armour?

How?

I can have my companions enter power armor that doesn't even have a fusion core inside and they go inside. It seems like fusion cores were made and intended only for the sole survivor.

As far as I can gauge from posts and gameplay.

Settlers have to be provided with some ammo, to start using the new gun, but does not consume ammo. You don't have to refill them.

Companions do use ammo and you might have to refill them. On the other hand... I think they pick up guns and ammo by themselves?

If settlers used up ammo what a pita! I don't think that's a bug.

Yes ammo use for settlers would be an serious bookkeeping for both the player and the game.

Fights can even auto resolve if you are not present to make this even more complex.

Settlers do need ammo to use gun but they do not expend it. Same for grenades. It's enough if they have single cartridge or grenade and they will use it indefinitely. Exception are some big guns like rocket launcher or fat man which do use up ammo.

You can not equip settlers with power armor but they will equip one during combat if it is nearby and have fusion core. But so will raiders attacking your settlement.

Its not/wasn't an exploit it's an intended game mechanic

I tested it at Red Rocket.

My Settler has a nice set of T-60 and a Minigun.

I gave them 400 rounds of 5mm, but despite shredding foes they have all of that left.

Don't know if they need at least 1 round, but they don't appear to use it up.

I don't think you can put Settlers into power armor on your own but, I have heard that if the settlement is attack a settler could jump into a set of PA if it was close (can't confirm that). Currently I have 17 settlers at the castle and each one is equipped with Combat armor (some standard, some sturdy & some heavy) and either a 44. magnum, short combat rifle or 50. cal Sniper rifle. I'v only had my Settlement attack once by mutants with missile launchers and I didn't have any causalities.

How did you get the settler into the power armor frame???

I just give them laser pistols with 50-100 cells. They don't seem to go through to many.

Hmm. This means that I only need to give each of them ONE bullet in the caliber of the weapon I make them use. Or when "I just want to trade some items", leave them with only ONE bullet. Nice to know.

For any settler standing in a Guard Post, just park an unoccupied suit of PA next to him. The first time that guard has combat, he will jump into the empty suit and not exit it until you tell him to.

As others have already said, they need ammo, but will not consume it. I give everyone 3 ammo and they never run out. I don't know about missile launchers because they will blow stuff up, including settlers, turrets, and themselves.

Back in Fallout 3 your companions would need a certain amount (18) was the magic number, if you gave them 17, they would use them, if you gave them more then 20, they would use them, I remember only putting 18 rounds of ANYTHING on them (including missile's) and they would never run out.

My "guardsmen" settlers in every settlement are loaded with 18 missiles each, and have gotten into many fire fights.

I checked them after each fight and no missiles where used up, even tho they were almost blowing me up with them.

Confirmed

Settlers will not use up any ammo you give them.

EX: Give them Combat Rifles with around 20 rounds and a grenade

and even after a heavy settlement attack, they will not run out of grenades or ammo.

This works with Flamers, Rocket Launchers, Miniguns, and other Heavy Weapons.

If you go into settlement build mode, select a settler and then assign them to the power armour they get into it but immediate get back out of it.

If you leave it near their guard post with a fusion core in it they will get into it when under attack but as others have said, raiders can get into it too if they beat the settler to the punch.

With regard to settlers and ammo, all you need to do is give them one round of the ammo type required by the weapon you give them. This does not apply to companions as they consume ammo regardless of whether they are with you or not.

I've been collecting combat armour, institute lasers and normal lasers to equip all my settlers. Settlements look great when attacked at night, awesome light show.

leave power suits around the base with cores in and they will get in to them if they want to. I've not found a way to force them into them though.

At the castle (my headquarters) i have all my different suits in different paint jobs left without cores, then i have a line of suits with out helms all painted in the shark colours that i left cores in for settlers. as soon as the base came under attack from gunners 3 settlers jumped into suits and since then haven't left them. for whatever reason though they wont wear helms even if you give them to them. but its still cool having 3 big suits marching about