The shop has been getting the power ready for a road train. They have identified the locomotives that will be used, pulled them out from the ready tracks, and coupled them together in the proper order. Some of the units may be dropped off along the way to do switching at outlying yards, so it is important that they be arranged to facilitate any needed setout moves. The electrical m.u. jumpers have been connected, the air hoses made up, and the correct functioning of the air brakes has been confirmed. But, how can you be sure they will all carry "load?" A loading check was a frequently-employed prototype practice done to make sure that all the locomotives in a consist (all coupled and connected by m.u. jumper cables) will actually respond to the throttle and load without shutting down. All the units that will be operating as train power are put on line, the brakes are set, and the throttle advanced to a high notch for several seconds. The desired result is that all the locomotives produce power, and move (hopefully all in the same direction) against the applied brakes. Any unit that doesn't load is bad news. It is contributing nothing to the tractive effort of the lashup, and any unit that shuts down and alarms needs to be looked at before the locomotives are ready for the road job. It should be mentioned that this type of loading check has no relationship to load box testing, where a locomotive is connected by cables to a stationary set of resistance grids so that the prime mover and generator can be load tested without powering the traction motors.
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