Sundering Prefix Question

[Selacius]

The sundering prefix gives you a chance to hit with armor penetration. Now that ability itself has a chance to occur. What i am curious about is how exactly it works. Say you have a 10/10 sundering bow string on a bow.
You fire an arrow at an enemy, and have a 10% chance to "activate" the armor penetration. Say that you succeed and activate the armor penetration. Now do you actually penetrate their armor? Or with that arrow you have another 10% shot of actually armor penetrating?
If this is how it works, it seems AP will never actually occur, or if so it will be extremely rare.

[IBeJebus]

The sundering prefix gives you a chance to hit with armor penetration. Now that ability itself has a chance to occur. What i am curious about is how exactly it works. Say you have a 10/10 sundering bow string on a bow.
You fire an arrow at an enemy, and have a 10% chance to "activate" the armor penetration. Say that you succeed and activate the armor penetration. Now do you actually penetrate their armor? Or with that arrow you have another 10% shot of actually armor penetrating?
If this is how it works, it seems AP will never actually occur, or if so it will be extremely rare.

a 10/10 sundering mod will have 10% armor penetration 10% of the time. Easiest way to explain this: You swing your sword that has a 10/10 sundering mod on it. For every 100 swings,10%(in this example 10 swings) of those swings will have 10% armor penetration. Which means on 10 of those 100 swings your attacks will have 10% armor penetration and infilict more damage.

[Wandalf]

You got it almost right.
If the armor penetration is activated (10%, so 1 hit/shot out of ten), that hit/shot penetrates the armor for 10%.
My understanding of that last number is that actually 10% of the armorlevel is ignored, as if the victim had a lower armor at that moment.

So let's say the enemy has armor AL80, then IF the armor penetration activates (remember, 1 hit/shot out of 10), that hit/shot would injure the enemy as if he had only AL72 (10% out of 80 is 8).

But I suggest you check out SonOfRah's article on damage. I can't recall the exact location, but I think it's somewhere on the main GWOnline.net site.
That article has everything tested and explained.

EDIT : IBeJebus beat me to the answer :D