extension cable vs multiplug

extension cable

noun
  • A cable that can be used to extend a signal or power cable or move the connexion point for a signal or power source. 

multiplug

noun
  • An electric device that allows more than one plug to connect to a single socket by containing multiple similar sockets; particularly for mains electricity. 

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