extension cord vs extension lead

extension cord

noun
  • An electrical cord with a plug one end, and a single socket or a multi-port socket at the other end, used for powering one or more devices at a distance, too far from the wall outlet to be reached by the normal cords of the device or devices. 

extension lead

noun
  • extension cord 

How often have the words extension cord and extension lead occurred in a corpus of books? (source: Google Ngram Viewer )