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Limits of MU consists

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Limits of MU consists
Posted by Max Karl on Friday, March 26, 2021 10:43 PM

Throwing all practicality out the window, what is the limit to the amount of locomotives that can be online and consisted together? Could it theoretically keep going forever?

  Max Karl, MRL and BNSF

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Posted by MMLDelete on Friday, March 26, 2021 11:41 PM

I'm not the guy to answer this. But my guess is you could string as many as you wanted to.

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Posted by Flintlock76 on Saturday, March 27, 2021 8:21 AM

I've got a DVD shot in the early 2000's of a power move on CSX's River Subdivision, the old NYC West Shore Line.  There's eleven diesel units in the consist.  However, whether they're all under power or not is hard to tell.  I wouldn't think so, but you never know, do you? 

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Posted by BaltACD on Saturday, March 27, 2021 9:01 AM

Flintlock76
I've got a DVD shot in the early 2000's of a power move on CSX's River Subdivision, the old NYC West Shore Line.  There's eleven diesel units in the consist.  However, whether they're all under power or not is hard to tell.  I wouldn't think so, but you never know, do you? 

CSX rules allow upto 12 units to be place together in a engine consist.  CSX Train Handling Rules limit the amount of power that can be On Line and that limit is set by the maximum knuckle strength of kind of train being handled.  Unit coal trains are normally equipped with 'extra strength' knuckles; other types of cars are normally equipped with standard strength knuckles.

Today's AC traction diesel-electrics have the ability, when operating in MU, to exceed the capacity of the knuckle on a straight draft pull.  Something, that back in time was basically considered unthinkable.  As I recall, by rule, maximum tonnage for a train was determined by using the tonnage ratings for 2 AC units plus 1 Dash-8 in coal unit train service; in regular merchandise freight service maximum tonnage was the tonnage rating of 3 Dash-8's.

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Posted by CSSHEGEWISCH on Saturday, March 27, 2021 10:02 AM

Penn Central ETT's from 1968 and 1969 placed a limit of 24 traction motors on line for multiple unit operation.  The instructions also stated that individual motors could not be isolated to meet this limit.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
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Posted by zugmann on Saturday, March 27, 2021 11:34 AM

Max Karl
Throwing all practicality out the window, what is the limit to the amount of locomotives that can be online and consisted together? Could it theoretically keep going forever?

Wouldn't there be a point where it would take so long for the rear engines to release their brakes, that the first engines wouldn't be able to move and would stall/drop their load before the consist ever got moving? 

 The opinions expressed here represent my own and not those of my employer or any other railroad, company, or person.

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Posted by mvlandsw on Saturday, March 27, 2021 7:41 PM

I think I remember a limit of 15 units due to the voltage drop in the control voltages through the wiring and MU connecyions.

The air brake response can be delayed with more than 3-4 units. When running a large set of light engines I would use the automatic brake rather than the independemt brake. The automatic would apply the brakes much more quickly than the independent would on the trailing, units preventing them from banging against the leading units.

Mark Vinski

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Posted by BigJim on Tuesday, March 30, 2021 5:29 PM

zugmann
Wouldn't there be a point where it would take so long for the rear engines to release their brakes, that the first engines wouldn't be able to move and would stall/drop their load before the consist ever got moving?

Operating rules spelled out how many independent brakes may be in operartion in a consist. Personally, I never liked to cut in more than three six axle or five four axle units. This all depended on the makeup of the consist.

I think that one time I had a light unit move that had eighteen units. Going through getting everything set up took a long time.

.

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Posted by MMLDelete on Tuesday, March 30, 2021 11:02 PM

Deep down, I knew I really shouldn't have taken a stab at this! Smile

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