Can you non plenum rated wire in a space with a common unducted return air?

No, using non-plenum rated wire in a space with a common unducted return air is not advisable. Non-plenum rated wire can emit harmful fumes if it catches fire, which poses a significant safety risk in areas where air circulates for heating or cooling. Plenum-rated wire is specifically designed to meet safety standards for such environments, ensuring that it is less likely to contribute to fire hazards. Always adhere to local building codes and regulations for safety.