The description of Force Ballista says to make a spell attack, but if it's coming from a cannon, especially one in a different space, would it break sanctuary. If so, could you cast it on the cannon itself instead?

Quote from ToKuOh_Li >>

The description of Force Ballista says to make a spell attack, but if it's coming from a cannon, especially one in a different space, would it break sanctuary. If so, could you cast it on the cannon itself instead?

 
The cannon requires the owner of it to target a creature for the spell attack. Sanctuary says it's protections work when a creature targets it for an attack or hostile spell. So, Sanctuary does protect the warded creature from the cannon and it is the cannon's owner that makes the saving throw since it is they who are doing the targeting.

The cannon is not a creature, so you cannot cast Sanctuary on it.

Maybe I worded that poorly, I meant if an Artificer cast sanctuary on themself, would activating their Eldritch Cannon be an attack, and thus end sanctuary?

Quote from ToKuOh_Li >>

Maybe I worded that poorly, I meant if an Artificer cast sanctuary on themself, would activating their Eldritch Cannon be an attack, and thus end sanctuary?

 
Yes. It is still the Artificer choosing to cause damage to another creature. It doesn't matter if it is through a feature (like the cannon), a spell, a stone they picked up, a button they push in a device, or a magic item. They still made the decision and performed the action that resulted in damage to a creature.

The point of sanctuary is "if you do not harm a creature, you cannot be harmed by a creature".

I understand RAI, but RAW states "If the warded creature makes an attack or casts a spell that affects an enemy creature, this spell ends."

Technically this wouldn't include the Flamethrower, which is not referred to as an attack or spell. But the Force Ballista specifically says "Make a ranged spell attack."

I imagine the same question arises with summoned creatures and familiars. Does the fact that the cannon is not its own "creature" change this? Would the answer be different with a Homunculus or Steel Defender? Does Arcane Jolt change anything?

Sure, when you cut out bits that you don't like you can make a spell work better for you.

Unfortunately, if going by RAW you need to use the full text.

If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends.

And yes, cannon still counts as you doing damage. Otherwise Sanctuary would never be broken - "I didn't damage he creature, the sword did". - If the Artificer has Sanctuary and uses the cannon, or any feature or THING to cause damage to another creature, they immediately lose Sanctuary.

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Yes,summoned creatures are different because they are creatures. The cannon is not a creature, it's a tool you are using.

Or apparently when I'm looking at a dated pre-errata version of Sanctuary... Exactly why that was added, I imagine.

So as long as it's another creature dealing damage, Sanctuary remains. Even if it takes your action or bonus action?

Quote from ToKuOh_Li >>

Or apparently when I'm looking at a dated pre-errata version of Sanctuary... Exactly why that was added, I imagine.

So as long as it's another creature dealing damage, Sanctuary remains. Even if it takes your action or bonus action?

 
As a tip, check things on here before asking in forums. It's part of the free rules and this site is fully up to date with Errata (which has been out for over a year), it will prevent such confusion in future.

Sanctuary is only on the warded creature and breaks when the warded creature deals damage. Unlike tools/etc having a summoned/controlled creature deal damage to a target is still that creature dealing the damage not the one with the ward. Even if it is controlled a creature has its own will and using its will, be it free or not, to target and cause damage to another. The same is not true for the damaging spell, sword, or cannon etc - such things are not wilful creatures, so if you use them to cause damage, it's your will that is in play and therefore you are the one causing damage.

If you dominate a creature/summon creature/etc, then sanctuary yourself, the dominated creature can still damage and do anything you command without breaking sanctuary. Likewise, your ally, minion, created living construct, whatever, can damage things but the sanctuary on you will stay intact. As long as it is considered a creature, this is fine.

Tools/spells/cannons/machines/whatever that are not creatures have no will, so if you use them to cause damage, bye bye sanctuary.

Cannon = breaks sanctuary because it's not a creature, it's a tool.

Steel Defender = does not break sanctuary because it's a creature.

That clears up a lot. I didn't even think to double check errata. I was going straight from my physical PHB.

It's a shame I can't rely on what I purchased and keep on hand. But I suppose that's how everyone who got WGE feels now...

Sorry to be replying to an old thread, but here's a related question that I can't seem to find a definitive answer for. 

So the eldritch cannon counts as a magical object which receives directions from you to know what to target right? So would it be possible for another character/creature to take control of the cannon? If it really were just another magical item then another character would be able to handle it, make an intelligence, or arcana, etc. check and then they could use the item if they passed the check. Suppose the artificer was unconscious, would the cannon just sit there uselessly until it disappeared? Logistically, I could imagine an artificer giving a "remote control" to an ally, allowing them to control the turret in an emergency, but given how the mechanics of the game often work, I wonder if I'm simply overthinking this and it's just impossible. 

Quote from citadelmark16 >>

So the eldritch cannon counts as a magical object which receives directions from you to know what to target right? So would it be possible for another character/creature to take control of the cannon? 

The description of the Eldritch Cannon ability includes "On each of your turns, you can take a bonus action to cause the cannon to activate if you are within 60 feet of it. As part of the same bonus action, you can direct the cannon to walk or climb up to 15 feet to an unoccupied space, provided it has legs."

There is no mention of other creatures having any way to control it.

So it does nothing if the creator doesn't instruct it using their bonus action.