Capacitor

This spell allows the caster to place an electrically charged trap on a box made of any nonconductive material. The electrical charge will be delivered to the first mass of metal of greater than one pound that comes within 10 feet of the box. If two or more such masses are within 10 feet, the charge is delivered to the largest mass.

The electrical charge delivers 3d8 points of damage, plus 1 hit point per level of the caster, to the creature carrying or wearing the metal mass. A saving throw vs. spell is allowed; if successful, the spark is harmlessly grounded (at the DM's option attracted to the next mass of metal large enough and close enough to trigger the box). The box is not damaged by the spell in any case. If the box is destroyed, any undelivered charge is lost.

The material is a bit of phlegm from a blue or bronze dragon. After the casting has been completed, the caster speaks a final command word while still within the spell range of the box. This command word activates the charge. The largest size box that can be affected is 8 cubic feet per level of the caster (for example, 3x4x8 feet at 12th level).

Notes: Very rare. (Updated from Dragon Magazine)