Are portable electrical outlets permitted in a basement?
You will need to have to provide proper strain relief of the flexible cord that drops down:

(from the NEC)  


  *368.56(B) Cord and Cable Assemblies. Suitable cord and cable assemblies approved for extra-hard usage or hard usage and listed bus drop cable shall be permitted as branches from busways for the connection of portable equipment or the connection of stationary equipment to facilitate their interchange in accordance with 400.7 and 400.8 and the following conditions:
  (1) The cord or cable shall be attached to the building by an approved means.
  (2) The length of the cord or cable from a busway plug-in device to a suitable tension take-up support device shall not exceed 1.8 m (6 ft).
  (3) The cord and cable shall be installed as a vertical riser from the tension take-up support device to the equipment served.
  (4) Strain relief cable grips shall be provided for the cord or cable at the busway plug-in device and equipment terminations.


Strain relief solutions are generally in the form of a metal finger-trap cages that tightens when the cable is pulled. for example: