SRD:Rod of Excellent Magic
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Once per day when casting a nonepic or epic spell that has an experience point component, the rod supplies up to 2,000 XP, not the caster. If more experience points are required to cast the spell, the caster provides them. As a special use of the rod, the caster can substitute the power inherent in the rod for the experience point development cost of an epic spell. Doing so drains all the power from the rod, rendering it useless.