Vertically, holes should always be inside the middle 1/3 of the joist, and hole diameter should never exceed 1/3 of the actual (not lumber dimensional) height of the joist.
Horizontally, holes may be anywhere along the joist except within 2" of the supported ends. Notching is not allowed in the middle third of the span, but holes are.
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Running wire through floor joists. - DoItYourself.com Community Forums