What NEC article covers allowable voltage drop?

Voltage drop is addressed in informational notes: NEC 210.19(A) for branch circuits and 215.2(A) for feeders both recommend a maximum 3% drop on the branch or feeder and 5% combined. Article 647 and 695 (sensitive electronic equipment, fire pumps) carry enforceable limits. The general 3%/5% figures are recommendations, but most AHJs treat them as design requirements.