plugboard vs switchboard

plugboard

noun
  • An array of jacks or hubs into which patch cords can be inserted in order to complete electrical circuits. 

switchboard

noun
  • A large piece of power-distribution equipment that directs electricity to multiple loads. 

  • The electronic panel that is used to direct telephone calls to the desired recipient. 

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