Locomotive lashup restrictions imposed after unknown incident - Trains Magazine

The limit on mu'ing units together is 10, power axles or rather rated power axles, and dynamic axles is a different topic altogether. When one mu's locomotives, we are talking about tying them together electrically, and by locomotive and brake pipe air. there are 4 air hoses and 1 electrical connection to make. When mu'ing locomotives together running the air through all of them is not practical, so you can put more than 10 locomotives on the point but only the head ten can be mu'ed the rest are treated like box cars.

Now since we have said that, why would you ot want to run the locomtive like a boxcar, number one and probably the only relevant reason when you would make a reduction in automatic air, the breaks would set up, you would not be able to actuate the air off so the brakes would set and possibly slide the wheels. Not a real big deal if it happens to a boxcar, but a locomotive much bigger deal as it is more costly to replace the wheelset.

I have skimmed over some of the issues but the biggest issue they I know of is the fact that air runs like crap through more than 4 or 5 locomives, causing some problems with setting and releasing air in switching, and also the fact that the retarding force on the train when using locomotive brakes can become very large very quickly with lost of locomotives and therefore causing severe buff forces on the cars i.e. cars being pushed off the track due to large in train forces.

just my 2 cents,