When does one "overcharge"?

There's alot out there on the topic of Overcharge(OC) but I'm curious if anything has changed since pre-launch. That and I haven't found one that covers this specific question:

What determines the value at which you begin to overcharge a primary attribute?

Does the OC value remain the same despite attribute point (AP) distribution? (Ex: Character A is lvl 10 and his AP is 9/0/0, character B is lvl 10 and has 0/9/0; do both characters begin to OC at 200 Magicka, or does Character A have a higher OC value?)

Why I'm asking this is because as I'm leveling in this game, at times I've found it entirely TOO easy to overcharge a stat. I'm currently Vet3 and am running 0/49/0 in AP distribution and my Magicka is getting overcharged. I've slowly stripped away mundus stone (Mage), attribute points and now enchants; but at this point I'm getting the feeling that I'm missing something. I lack the playtime to test this myself so I appreciate any and all contributions to the discussion.

You don't necessarily want to avoid overcharging a stat.  I'm not the best theory crafter out there but here's how I think of it.  If my primary role is healing and I have enough health to survive, then I start stacking regen for sustain, and then in ESO's case I'd stack magicka and crit for bigger heals.  Where I get my magicka pool from doesn't matter in terms of whether or not its overcharged - the values are the same from points or stones or runes.  But overcharged only means I've hit the "softcap" where 1 point of magicka isn't equal to 1 point of magicka before overcharge.  If I have enough of the things that keep me alive  plus enough of what sustains my output, increasing my pool size + healing value is still more valuable to me than say switching to stamina just because it isn't overcharged.  

My goals no matter what role I'm playing when I design a character's stats are to 1) have enough health to survive the length of the fight 2) Have enough regen of whatever primary resource I'm using to be able to last and be useful for the extent of the fight and 3) Increase throughput whether that's avoidance/mitigation/threat generation for a tank, heal value for a healer, or dps value.  

Short answer - yes oc value remains the same :)

Also, enchant values are something to consider when at overcharge on a stat and boosting that stat.  For instance, if you are in the OC zone for Magicka, and have the mage, and are wanting to enchant for magicka, using the divines enchant will net you a bigger magicka gain than if you went with a magicka enchant (Tested up to PURPLE quality gear, white enchants only so far.)
That is to say, depending upon what stat you want to increase, what mundus stone you are running, and the numbers of the enchant, using the mundus stone boost may be more effective.

As for the Oc in general, my main sorc has put just about everything at every turn into Magicka.  It rocks for PvE, although I have to be careful about strong power attacks or while in AvA.  Simply put, unless you lack a given stat (mostly health for non-tanks for pure survival) then it really doesn't matter.  0.4 is still >> 0.  And, if you are putting stat points into something you never need, then you are getting a 0.