Pappie's 70K Arc (Life based - no Void battery) 1.3

They work for spells too.
You can see a change in your tooltip DPS when adding crit multiplier (with a certain crit chance it is quite strong) if you need proof.

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Tommie_Sjukskriven wrote:

It doesn't matter if a monster is overcapped since light pen cuts of the max res and their overcapped res doesn't matter

I checked it out, you are correct. When testing the effectiveness of lightning penetration and PCOC I didn't notice any difference though. Can certainly replace PCOC with ligthning penetration and run assassins mark on the curse on hit setup, although in groups you will rarely gain any charges.

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CallMeHi wrote:

I have one question about the passtive points. I see many Crit Arc builds adding "increased critical strike multiplier". Are these points for attack not spell, aren't? Why you add these?

As Carmondai said, crit multiplier is global (unless noted otherwise on nodes or gear) as are some generic critical chance nodes. Crit multiplier works best when you have sufficient critical strike chance.