So I've been playing on a full PvP rank up server running Minecraft version 1.5.2, and the maximum enchantment level available there is 25. However, I didn't notice any change between Protection 10 and 25.
Are enchantment levels beyond 10 any more effective than 10?
Best Answer
No, Protection type enchantments are capped, and the cap is fairly low.
Damage reduction based on Armor and Armor Enchantments has some peculiar mechanics which are detailed on the Minecraft Wiki page for Armor1 (some emphasis mine).
The "TypeModifier" in the equation depends on the enchantment itself, and is 0.75 for Protection, 1.25 for Fire Protection, 1.5 for Blast and Projectile Protection and 2.5 for Feather Falling.
Note how the EPF is capped twice. We can't do anything about the random number multiplication and the subsequent second cap, but we can make sure to have an EPF of at least 25, to ensure maximum Protection. Using the above formula, we can calculate the EPF for a single armor piece with a certain Protection enchantment level.
From this table, it is immediately evident that you can reach the EPF cap with a single Protection X enchantment. Anything beyond Protection X has no effect on the game mechanics.
Using a full set of armor, and optimizing for lower enchantment levels, you can reach cap with 3 Protection V and 1 Protection IV enchantment (3*7+5=26).
1 This part of the page has been roughly the same in March 2013, when 1.5 was released.