In the electrical diagram, MR means that the line is laid along the metal wire groove. An Electrician must know Electrical Abbreviations and Full Forms to read a electrical drawings. The mechanical and electrical characteristics, tests, certifications, overall quality management, recommendations mentioned in this technical guide only apply to our own cable management ranges and cannot under any circumstances be transposed to si osure, overheating or. AC – This stands for alternating current, which reverses its direction in constant intervals. Al or Alum wire - Alum is short for aluminum.