Only Short Circuit really drains enough to merit slotting for Endurance Modification, and even then, only if you're combining it with either Power Sink from the Electricity Manipulation pool or Power Boost from the Energy Manipulation pool.
If you have a different secondary it's probably not worth slotting for endurance modification at all. By the time you have drained the bad guys either you could have killed them, or they will have killed you.
I've got my elec/elec to 33 and have done a fair amount of end drain testing, but still can't be conclusive. Unfortunately I've not found any end drain figures anywhere, and I'm not sure how you'll get definites. From my experience, all elec powers will drain some end, it's mostly a case of trial and error as to how much you get. personally I slot for a mix of drain and damage in certain powers. Short circuit is all end drain and I've slotted ball lightning and tesla cage for some drain as well, as their damage is low so I figured not worth slotting for damage as much.
Generally when soloing I'll be killing mobs before I can drain them, so it mostly comes into play in teams where I may need to drain bosses. In such a case hopefully the tank can keep the aggro off me long enough for 2 short circuits.
A note on short circuit, the acc. is pretty high for AoE but generally it's good to fire off Aim before hand. It does seem to get a lot more aggro than other AoE powers I've tried, so make sure your tanks got their attention good.
I'll hopefully be ding 35 this week, in which case I'll let you know how power sink influences my play style.
Hi,
I have asked this before but my search-fu is weak today 
Your two main end drain powers are short circuit and power sink. Firing these two off in a group will drain all of their end, with the benefit of giving you end because of power sink (even if the mob has no end left, power sink still gives you end at the normal rate).
I personally have not tried this yet, but will soon (in a level or so). As a test, I have slotted tesla cage for end mod too, and it can drain just under a 1/4 of end from a mob, but to be honest, once you have reached power sink levels all your other powers should be enough to keep them at 0 end on their own... at least till they are "arrested" shortly after.
I recommend slotting for damage and accuracy, recharge or end reduction if you need more endurance but with power sink you should have all the end you need with all the mobs standing around in convenient little groups 
SC with 3end mod (how I got it slotted) + powersink 3 endmod = complete spawn dry of end. In the rare occasion some boss still has a sliver of end left, tesla cage and electric fence are your friends in end draining. IIRC from the elec blast powers, apart from SC and TB, tesla cage has the highest drain. Elec fence is nice because it gives 4 ticks of end drain, off the top of my head 4x 2.5, but please correct me if I'm wrong. So effectively elec fence can even be used as a kinda primitive -recovery power.
Of course Thunderous Blast is the king of ranged drains.. but then again, they aren't gonna do much anymore after you fry em with thunderous blast 
"god, how many devs did hami have to sleep with to get ED?"
Total Cat @Stagefright
Title says it all realy, just wondering if slotting End Mods in Elec/ Attacks is usefull at all?