Is spanking a child with a belt in Pennsylvania legal?

Yes. According to the PA Civil and Criminal Codes: "Parents can use reasonable supervision and control when raising their children. 23 § 6302. [Civil Code] Parent/guardian/person responsible for general care and supervision/ person acting at request of the above may use force for the purpose of safeguarding or promoting welfare of minor including the prevention or punishment of his misconduct, if the force is not designed to cause or known to create a substantial risk of causing death, serious bodily injury, disfigurement, extreme pain, mental distress, or gross degradation. 18 § 509. [Criminal Code]"