Original

Travel Through the Wires: Give Electro a power action. Place him in the same square as any unheld object on the map.

Arc Lightning: Give Electro a power action and make a ranged combat attack against a single target using his printed damage value. Each time he hits, after actions resolve, he may then make a ranged combat attack as a free action against another single target as if he occupied the previously hit character's square, replacing his range value with his printed range value minus the number of characters he has hit this turn with this power.

Errata

Arc Lightning: Give Electro a power action and make a ranged combat attack against a single target using his printed damage value. Each time he hits, after actions resolve, he may then make a ranged combat attack as a free action against another single target as if he occupied the previously hit character's square, replacing his range value with his printed range value minus the number of characters hits he has hit made this turn with this power.

If Electro uses Arc Lightning and keeps attacking the same two adjacent characters, can I potentially make as many attacks as I want as long as I keep hitting?
No. That was never intended and the power was changed to reflect the intent. Each HIT now descreases the range value, so you will have at most 7 attacks.

But what if I modify his range value? Can I get more hits that way?
Because of the Golden Rule called Replace Then Modify, you would first replace his range value with 7-x (where x is the number of hits), then factor in any modifiers. Yes, this means you could potentially get some more hits in with Arc Lightning.