A karni na 18, masana kimiyya sun dauki wutar lantarki da maganadisu a matsayin al'amura biyu na zahiri da ba su da alaka da juna. Bayan da masanin kimiyyar lissafi dan kasar Denmark Johann Gerhard Oersted ya gano tasirin maganadisu na wutar lantarki a shekarar 1820, masanin kimiyyar lissafi dan kasar Burtaniya Michael Faraday ya gano induction electromagnetic a shekara ta 1831. Wadannan binciken sun tabbatar da cewa makamashin lantarki da karfin maganadisu na iya canzawa, wanda ya kafa harsashin bunkasa injinan lantarki da janareta daga baya; dan Adam ta haka ya shiga zamanin wutar lantarki albarkacin wadannan abubuwan kirkire-kirkire. A cikin 1830s, masanin kimiyyar lissafi ɗan ƙasar Amurka Joseph Henry ya ƙirƙira relay yayin da yake nazarin kula da da'ira ta amfani da abin da ya faru na shigar da wutar lantarki. Na farko relays su ne na lantarki relays, wanda yayi amfani da al'amarin na tsara da kuma bacewar ƙarfin maganadisu a cikin electromagnets lokacin da aka ƙarfafa da kuma de{7}}ƙarfafa don sarrafa buɗewa da rufe wani babban ƙarfin lantarki, mai girma{9}} na yanzu. Zuwan sa ya ba da damar gudanar da aiki mai santsi na sarrafa ramut da kuma kariyar da'irori. Relay wata babbar ƙirƙira ce a cikin tarihin kimiyya da fasaha na ɗan adam; ba kawai tushen injiniyan lantarki ba ne amma kuma muhimmin tushe ga fasahar lantarki da fasahar microelectronics.
Relay shine na'urar sarrafa wutar lantarki wanda, idan aka ba da ƙayyadadden adadin shigarwa kuma ana riƙe shi na ɗan lokaci, yana haifar da canjin matakin da aka ƙayyade a cikin adadin da aka sarrafa a cikin da'irar fitarwar lantarki. Da zarar adadin shigarwar ya ragu zuwa wani matakin kuma an riƙe shi na dogon lokaci, zai koma yanayinsa na farko. Za a iya gano ainihin ƙa'idarsa zuwa ga ci gaban da aka samu a cikin electromagnetism a ƙarni na 19.
