Source: Starfinder Core Rulebook p.112
When you hit a target with a weapon in the shock category, electricity arcs out from your original target to deal electricity damage to a secondary subject within 10 feet of the original target. This damage is equal to the weapon's level. The secondary subject must be the creature nearest to the original target (your choice if multiple creatures are equidistant). This gear boost does not function for weapons that have the explode or blast special property. If you use this gear boost with a weapon with the arc critical hit effect, your secondary subject for electric arc must be the same as your secondary subject for the arc critical effect.