Motive Power Question-Multiple Units

[Stewartbf6]

I have a simple question I cannot find an answer to, (maybe because it is a simple minded question).

When observing train videos and real trains I sometimes find a large number of locomotives at there head or tail end, it's obvious that not all of them are necessary to pull the train and are probably being redistributed. My question when you have such redundant units, are they powered up? If so what are the advantages vs the cost of operations? If not powered, are they unwieldy freight cars comparatively? I looked for smoke, but a non powered or idling engine is hard to spot and be 100% sure. Of course in large power transfers of retired locomotives it is rather clear they are unpowered, but not in every case.

This is one of those nagging questions I have kept a look out for since I was a youngster hoping for an answer in an article or something, so far I haven't found it. If it is a simple minded question, please forgive me and provide an answer so my simple mind can finally rest and move on to other mysteries of life. Thank you.

 

[maruffijd]

It may be possible the over obundance is simply a power move while hauling freight.

 

[Dermmy]

In general trains are restricted to 24 powered head-end axles (assuming DC traction motors). AC traction motors count as 1.5 axles in the calculation and there are a couple of other variations but in principal any locos coupled behind the first 24 axles are dead or at best idling. Dynamic braking is (generally) restricted to those same 24 powered axles, though idling engines contribute to conventional braking.

Additional locos in the centre or rear of the train (DPU or Divided Power Units) are calculated differently and will be contributing both traction power and dynamic braking on loaded trains, but a long string of head-end power involves a power move (transfer of too many locos from Yard A to Yard B). On some roads the DPU units are moved to the head end on empties, on others they remain in-train but are idling.

Hope that helps...

 

[montanawestren]

Well on Bozeman pass MRL must have helpers on every train some exceptions may be the local. I know there is a weight thigy like trains over X lbs must have helpers. But sometimes the helpers arent needed but are still on the train. actually I have the same question if that dosent help.
MTW

 

[Stewartbf6]

So, 24 DC Axles, at 6 axles for 3 wheeled units or 4 for 2 wheels, would mean a maximum of 4 front end units and 2.66 AC Units???! Is there a traction on each axle, generally. Better yet is there a book or paper I can read to educate myself? Right know I think the answer is: Well, it depends.....

 

[norfolksouthern37]

So, 24 DC Axles, at 6 axles for 3 wheeled units or 4 for 2 wheels, would mean a maximum of 4 front end units and 2.66 AC Units???! Is there a traction on each axle, generally. Better yet is there a book or paper I can read to educate myself? Right know I think the answer is: Well, it depends.....

oh my. this could end up being a long thread!

no it doesn't quite work that way. on NS and i think CSX the max powered number is 24 conventional (non high-adhesion) axles. note that doesnt apply to unit trains or otherwise designated trains that say they can have more or less. on BNSF the limit is 36 but i have read it was changed to 42. i am unsure of other railroads.

i have a power chart for NS that lists each loco and its "power axle count"

most 4 axle units are 4 power axles, but those with super series tech are 5.
6 axle units like SD40-2s are 6 power axles.
SD50s to SD70s and Dash 8s etc are 8 power axles
new power like ES44s and SD70ACes are 9

 

[whitepass]

I remember an old story about a NYC train leaving Detroit with 4 locos but had to go back to the yard with 9 locos only one of witch was running, the other 8 broke down!

 

[mjolnir]

I have a simple question I cannot find an answer to, (maybe because it is a simple minded question).

When observing train videos and real trains I sometimes find a large number of locomotives at there head or tail end, it's obvious that not all of them are necessary to pull the train and are probably being redistributed. ...<snippage>...

It may depend in part, upon which train videos you are talking about. In the videos from the 1950's and 1960's, keep in mind that the horsepower of most of the units eing in the 1500 to 2000 horsepower range, and long lashups of power were more common than today, when horsepower of units can be more than three times this amount. Also, while some of the units you see are not being needed at the point you're seeing the train, it may well be that they are needed to handle the train at some point on the route, particularly these days, when it is more common to assign a set of power to a train for its entire round trip route.

I'm not sure about the restrictions to the number of axles on DC and AC units; these were not used on the RI when I worked there. However, the "power bureau" did have a reference book detailing for each class of locomotives on the railroad, how much tonnage it could handle over each subdivision. When a train was called at a certain point, the power bureau was notified of the tonnage on the train, and consulting this reference found how much power was needed to get the train over the road, and assigned power as needed. In most cases, the power requirements were governed by two or three segments on the route, which required a certain amount of power, while the remainder of the route did not require so much. In some cases, units could be taken off line, but in many cases, the power for the whole consist was throttled back.

It was rather easier on the RI to spot a non-powered engine. Operating rules provided that any locomotive moving dead in a train had to be separated from the live units by six cars.

ns

 

[ptrainman]

Ok here is a powered axle listing for most modern units.

Key:
1 Normal (DC non-High Adhesion) Axle=1 Powered Axle
1 DC High Adhesion (Hi-Ad) Axle= 1 1/3 Normal Axles
1 AC Axle= 1 1/2 Normal Axles

GP38/38-2 and GP40/40-2 (4 non Hi-Ad DC axles)=4 Powered Axles
SD40/40-2/40E/40M-2/40T-2 (6 non Hi-Ad DC axles)=6 Powered Axles
GP50, GP59, GP60, Dash8-32B, Dash8-40B (4 Hi-Ad DC Axles)= 5 1/3 Powered Axles
SD50, SD60/M/I, SD70/M/M-2, Dash8-40C/CW, Dash9-40C/CW, Dash9-44CW (C44-9W), ES40DC, ES44DC (6 Hi-Ad DC Axles)= 8 Powered Axles
SD70ACe, SD70MAC, SD80MAC, SD90MAC, AC4400CW, AC6000CW, ES44AC (6 AC Axles)= 9 Powered Axles

On Norfolk Southern the max number of Powered axles is 24 (3-6 Axle Hi-Ad DC units or 2.5-6 Axle AC units) on everything except unit grain trains shorter than 100 cars which are allowed to use 32 Powered axles (4-6 Axle Hi-Ad DC units or 3.5-6 Axle AC units). I am not sure about other railroads, but NS is the most restrictive of all of them when it comes to powered axles on a train.


Paul

 

[Stewartbf6]

WOW, Thanks to all for your responses and sharing of life experiences. Not a simple question, but a simple mind trying to grasp all of this. i will try to explain what I have learned...,no that will take to long. let me sum up:

1) How much power applied to a particular train is dependent, at least partially on, RR's rules, tonnage (of course), route, power rating of units.
2) Modern Locos with more HP and super duper computerized trucks that suck themselves onto the rail, (High adhesion), as well as A/C traction motors have higher power ratings
3) Power Rating numbers do not have to equal actual axles, but should never be less.
(Why do they limit the number of powered axles. does it tear up the rail?)

So, if I see a larger than normal number of locos on the head end I can assume that they may be part of a power transfer, are probably running but throttled back, within the companies power rating limits, enjoy the train and go about my day. Thanks everyone.

 

[ptrainman]

They limit the number of powered axles on the headend of a train so the train does not get tore in half from to much power. Railroads also have powered axle limits for pushers/helpers. On Norfolk Southern, you can only push with 16 powered axles (2-6 Axle Hi-Ad DC units or 2-6 Axle AC units with 2 traction motors cut out) except on certain territories you can use 24 (3-6 Axle Hi-Ad DC units or 3-6 Axle AC units with 3 traction motors cut out). I have heard that on AC units you cant cut out individual traction motors like you can on DC units, you have to cut out the whole truck which is 3 traction motors. Not sure if that is true but I have heard that from a couple NS engineers about the new ES44AC they have. This may be a NS thing though.


Paul

 

[jjanmarine3]

Hi, a little late but I only saw this interesting question now and I also want to lay an egg here to add to all the other correct answers.
A system was developed on diesel traction in South Africa ( I forget the name of the system now ) where the driver of the leading unit has a control box that can power up or set any locomotive in a consist without getting out of his cab ( remotely ) as he ( or she lately ) wishes.This was done by modifying the existing MU cables with extra wiring .The driver would know which loco's are idling and which are powered by led's that lit up on this control box in the cab.It was tested and proven that this saved fuel . Sometimes loco's would be shutdown when they would idle longer than certain stipulated periods while waiting to save fuel.
With the price of diesel it payed to do this on certain sections on a route depending on the power needed, which obviously differs . Drivers have to undergo route knowledge tests regularly ( like every six months ) to make sure they know the routes rules and limits well.
An interesting fact too about steam traction is that every time 'Big Boy' worked a load over a line a repair train had to follow to fix the line which was stressed out by all that power, especially on the curves. Another interesting thing is that irrespective of how a loco is coupled ( cab to nose or nose to cab ) they would all work together in reverse or forward. This is because the wiring in the mu boxes on each end are crossed ( trainlined ) for that purpose.
Cheers
Jan

 

[UPRails834]

I have heard that on AC units you cant cut out individual traction motors like you can on DC units, you have to cut out the whole truck which is 3 traction motors. Not sure if that is true but I have heard that from a couple NS engineers about the new ES44AC they have. This may be a NS thing though.

Actually it's the other way around. You can cutout individual traction motors on AC units but you never have been able to do that on DC locomotives. On DC locomotives you can only cutout the entire truck.

It's interesting to read the powered axle requirements on the Norfolk Southern. Apparently the different railroads make up their own powered axle numbers because on the Union Pacific our max EPA (Equivalent Powered Axles) is as follows:

Intermodal Trains - Head end 62/Cut-In 48/Rear Helper 23
Manifest Trains - Head end 52/Cut-In 48/Rear Helper 23
Empty bulk unit trains 52-36-24
Loaded bulk unit trains 52-55-28

Some examples of the individual unit EPA's are:

Most GP units are rated 4.5 but GP60's are 8.
SD40-2 = 7.1
SD50 = 9.2
SD60 = 9.9
SD70/SD70M = 10.4
SD70ACe = 12
C44AC-C45AC-C60AC = 12.1
ES44DC = 11.5

Again these are Equivalent Powered Axle numbers and not the Equivalent Dynamic Brake Axles which are a entirely different set of numbers.

When observing train videos and real trains I sometimes find a large number of locomotives at there head or tail end, it's obvious that not all of them are necessary to pull the train and are probably being redistributed. My question when you have such redundant units, are they powered up?

Sometimes what you are seeing are units that are DIC (Dead In Consist) or DIT (Dead In Transit) which means they are shutdown and not running either because they are defective and are being sent to a repair facility or it is a power move. Because of the high cost of fuel nowadays any excess units not needed to move the train are to be isolated and/or shutdown completely. On the Union Pacific there are numbers (which to fully explain would require too long of a post) provided for a given section of railroad and each train should be near that total number with its power. If your train's power number is below the set number for the territory it is under powered and won't make the grade or speed requirements. If the number is above the territory requirement then you are supposed to cutout traction motors or isolate units to conserve fuel.

 

[ptrainman]

Actually it's the other way around. You can cutout individual traction motors on AC units but you never have been able to do that on DC locomotives. On DC locomotives you can only cutout the entire truck.

You can cutout individual traction motors on Norfolk Southerns ES40DC and Dash9-40CW units because I have seen it done. It may be another Norfolk Southern thing though since these are NS only units. A couple months ago a traction motor on a pusher unit caught on fire and it was cut out for the rest of the trip. Norfolk Southern is backwards on power limitations. UP limits seem alot more reason able. Granted UP runs in more mountainous area NS still has some heavy grades that are hard to climb with thier limits. NS does not allow different limits for different types of trains, its all the same except for the 100 car or less grain trains.



Paul

 

[norfolksouthern37]

you cant cut out individual traction motors on EMDs AC locomotives, only the entire truck at a time.

 

[UPRails834]

you cant cut out individual traction motors on EMDs AC locomotives, only the entire truck at a time.

Yes you are correct. Originally in my post I had wrote "GE AC units" but for simplicity I shortened it to "AC units".

As a further note on the UP you cannot cutout DC traction motors for EPA or EDBA requirements. They can only be cutout if defective. On AC units only motors 1, 2, and 3 can be cutout for EPA as 4, 5, and 6 can only be cutout if defective.