[3.5] Armor enhancement bonus and when it applies

[Dac]

This question recently came up during character design, and it's something that I've never really looked at before:

If I am wearing a suit of padded leather +5 armor and cast Mage Armor, does the armor bonus from the spell replace the armor bonus of the padded leather (1) while still allowing me to apply the +5 enhancement bonus?

SRD says this on magic armor: "Magic armor bonuses are enhancement bonuses, never rise above +5, and stack with regular armor bonuses (and with shield and magic shield enhancement bonuses)."

To me, the rule seems to suggest that the Mage Armor would indeed overwrite Padded Leather +5's inherent armor bonus while keeping the +5 intact, but my DM disagrees and has said no, no dice, end of story.

Although I'm not going to argue with him anymore, I'm curious as to whether I was wrong or not.

[drengnikrafe]

An invisible but tangible field of force surrounds the subject of a mage armor spell, providing a +4 armor bonus to AC.

You are correct. Mage armor will increase your AC by the difference between padded armor and the +4 that mage armor grants (so 3), and at the same time keep around your enhancement bonus. The only thing mage armor doesn't stack with is real armor, but there's nothing to say you can't keep wearing armor while you have mage armor active. Unless there's some weird ruling I missed somewhere.

[Marnath]

I don't think armor enhancement stacks with the spell...

[Gorgondantess]

I don't think armor enhancement stacks with the spell...

An enhancement bonus to AC stacks with an armor bonus to AC. With mage armor and +5 padded armor, you'd have +9 AC: 5 from the +5, plus 4 from the mage armor.

[Snake-Aes]

The enhancement applies to the armor. Thus a +3 chainshirt has a +7 armor bonus.
Here, rules compendium quoting.
AC formula:

AC = 10 + size modifier + Dex modifier + armor bonus +
shield bonus + deflection bonus + insight bonus + natural
armor bonus + dodge bonuses + other modifiers

Note that it doesn't separate "enhancement". Enhancement bonuses increase the item's type's value, not a separate "enhancement" slot.

Enhancement Bonuses
An enhancement bonus makes an armor bonus, natural
armor bonus, or a shield bonus better. The enhancement
bonus stacks as if it were part of the bonus to which it
applies—armor, natural armor, or shield—so it’s not included
in the AC formula above.

[Dac]

Okay, so it's an enhancement bonus that enhances another bonus.

Not how I read it from the SRD, but I guess that makes sense.

[Snake-Aes]

Okay, so it's an enhancement bonus that enhances another bonus.

Not how I read it from the SRD, but I guess that makes sense.

Yes, the enhancement is bound to the item, not the character. I got confused like that the first time when i saw the amulet of natural armor, since it gives an enhancement bonus to natural armor.

[Douglas]

Yeah, armor and shield enhancement bonuses apply to the armor or shield bonus, not directly to your AC. In the situation outlined in the original post, you have a +6 armor bonus (+1 base, improved by +5 enhancement) and a +4 armor bonus, and you only get the +6.

Edit: And yes, similar logic is why the Amulet of Natural Armor is not useless to creatures that already have a natural armor bonus. The AoNA gives an enhancement bonus to the base natural armor bonus, combining into a higher bonus, rather than providing a direct natural armor bonus which wouldn't stack.

[aeauseth]

Typically you dont use Mage Armor while wearing normal armor, but there is one exception. Mage Armor is a force effect and protects you from incorporeal creatures, while normal armor doesnt.

[aeauseth]

So Padded Armor +5 is AC 16 (1 armor + 5 enhancement). If you cast mage armor then you have AC 14 (4 armor +0 enhancement). You get the best of the two (AC 16 or AC 14), so AC 16 in this case.

The enhancement bonus only affects the Padded Armor. You can't use the +5 enhancement bonus for the Mage Armor, it's only usable with the Padded Armor.

[Keld Denar]

Typically you dont use Mage Armor while wearing normal armor, but there is one exception. Mage Armor is a force effect and protects you from incorporeal creatures, while normal armor doesnt.

If you are gonna do this, use Ectoplasmic Armor (SpC) instead. It provides a much higher bonus, and, unlike Mage Armor, is an Abjuration that grants and armor bonus, so it IS subject to Abjurant Champion's Abjurant Armor class feature. MUCH better bonus in all cases.