Multi-Unit Cable (MU Cable)

A multi-unit cable, or MU cable, is the electrical jumper cable used to connect locomotives coupled together so they can be operated as one unit. It is the electrical link that makes multiple-unit, or MU, operation possible.

Where It Sits

The MU cable plugs into a receptacle at the end of one locomotive and into the matching receptacle on the adjacent locomotive, bridging the gap between them above the coupler. When several locomotives are coupled into one consist, an MU cable is connected between each pair so the electrical control circuits run continuously through the whole group. It is a separate connection from the brake pipe and other air hoses, which carry the pneumatic side of train control.

What It Does

The cable carries the control signals from the lead locomotive's control stand back to the trailing locomotives. Through it, commands such as throttle position, direction, and other control functions are passed from unit to unit, so that one crew in the lead cab controls the power output of every locomotive in the consist at once. This lets railroads add locomotives for more tractive effort without adding crews.

Inspection

The MU cable and its receptacles must make a clean electrical connection for the trailing units to respond correctly, so damaged cables, bent pins, or dirty contacts are corrected. As a control-circuit part, it is maintained so that multiple-unit operation stays reliable; related requirements fall under the applicable railroad and AAR standards.