If a character wears a magic item created with a particular spell, then cast the same spell, does the character gain both effects?

Question

This is a general question on whether the effects from a spell stack with the effects of a wondrous item that was created with that same spell, in case the item's effect is different from the spell itself.

Example: The monk's belt (DM 240) is a wondrous item created with either the spell righteous might or the spell Tenser’s transformation. The effect is as follows:

This simple rope belt, when wrapped around a character’s waist, confers great ability in unarmed combat. The wearer’s AC and unarmed damage is treated as a monk of five levels higher. If donned by a character with the Stunning Fist feat, the belt lets her make one additional stunning attack per day. If the character is not a monk, she gains the AC and unarmed damage of a 5th-level monk. This AC bonus functions just like the monk’s AC bonus.

Looking at the item characteristics, they are different from the benefits of the spell righteous might.

Now, the wearer casts on himself the spell righteous might.

Does this mean that the monk/cleric wearing the belt will also gain the benefits of the righteous might spell too?

how would it work if some effect between the spell and the item were "the same" and some were not?

Answer 1

You gain none of the benefits of the spell used to satisfy prerequisites unless the item says you do

That section of the item description describes the Prerequisites to craft the item. You can't make it at all without those prerequisites, but even if a particular spell is part of the prerequisites, it's only needed during crafting and the particular spell used to provide the prerequisite has zero effect on the resulting item (beyond enabling its creation in the first place). The item provides the described benefits of the item, the spell used to create it is irrelevant.

Read the prereqs for a few of the other items and you'll quickly realize that it would be ridiculous if they provided the full effect of their prerequisite spells as a permanent effect. For example, the Belt of Dwarvenkind requires tongues; a described benefit of the item is to understand, speak and read Dwarven, but aside from granting literacy, that benefit would be largely redundant with tongues. Does it seem reasonable that wearing such a belt would make you able to speak and understand all languages, not just Dwarven? A Brooch of Shielding, which absorbs up to 101 points of damage from magic missile, is made with shield, which blocks magic missile entirely, so if you got a permanent shield effect, why would the damage capacity matter?

Given that, the wearer of such an item is not under the effect of any of the prerequisite spells (unless the item description says otherwise), so they're eligible to have those spells cast on them just like anyone else.