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Cable connections on loco

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Cable connections on loco
Posted by Lithonia Operator on Sunday, May 10, 2020 11:00 PM

I was looking at a pic of a switch engine in the current Trains. It's an end-cab switcher, we're looking at the cab end, and it's headed almost straight at the photographer.

On the vertical surface of the cab, above platform level, are two caps which are clearly covering cable sockets, one on each side of the steps going up to the cab from the platform.

One says "Dummy", and the other says "AAR". What are those for?

Still in training.


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Posted by Overmod on Sunday, May 10, 2020 11:26 PM

I don't have the picture, but I bet that it's for storage of an MU cable (connecting between AAR sockets) when 'not in use' -- the trailing end would plug into that 'dummy' socket.

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Posted by MMLDelete on Monday, May 11, 2020 10:29 AM

On closer inspection, I don't think those sockets are on the cab. They are on boxes (battery boxes?) that are bolted to the railing. So maybe it's for if the engine needs a jump, or needs to give a jump.

The photo is a two-page spread with the article about the New York & Atlantic RR. Great shot.

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Posted by jeffhergert on Monday, May 11, 2020 4:40 PM

Overmod

I don't have the picture, but I bet that it's for storage of an MU cable (connecting between AAR sockets) when 'not in use' -- the trailing end would plug into that 'dummy' socket.

 

I don't know that I've seen one marked 'AAR', but I have seen the ones marked dummy.  It is for placing the MU cable when not in use. 

Some engines have two dummy sockets.  This is because a bad MU cable plugged in, even if not connected to another engine can cause problems. 

Leaving the unplugged end of an MU cable loose, draped over the uncoupler lever for example, is a Federal defect. 

Jeff   

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Posted by SD70Dude on Monday, May 11, 2020 5:03 PM

jeffhergert

Some engines have two dummy sockets.  This is because a bad MU cable plugged in, even if not connected to another engine can cause problems.

We had an incident caused by that a couple years ago.  The locomotive in question would not stop loading (pulling) when the Engineer throttled down to idle and centred the reverser.  She ended up having to put it in emergency to get it to quit. 

After that a bulletin was issued instructing crews to never leave MU cables plugged in to the 'real' socket when not in use.

A number of our units have the two 'dummy' sockets so far apart that it is almost impossible to get the two ends of the cable to reach.  Other, even older units don't have them.

The cause behind incidents like this is usually a MU cable that has been damaged, so that some of the individual wires inside are touching each other.  This can allow stray current to get places where it should not, and make even a single locomotive act like it is receiving commands from another.  A common way for the cables to become damaged is for them to be crunched between drawbars when hanging too low on the end of a locomotive.

jeffhergert

I don't know that I've seen one marked 'AAR', but I have seen the ones marked dummy.  It is for placing the MU cable when not in use.

I've read that the AAR standard MU trainline is 74vDC, and of course the pins will be arranged in a specific way.  But, even today, not ever locomotive conforms exactly to those standards. 

The main functions (throttle, dynamic braking, penalty brake control, etc) have been standardized for many years, but there are still issues with certain more specialized features like Pacesetter (automatic slow speed cruise control). 

I used to work in a terminal where we loaded unit trains on a daily basis.  Older locomotives (GE Dash-8 and Dash-9, EMD SD60, SD70 and SD75) could not be relied upon to work together properly in Pacesetter with anything else except each other.   

Motive power eventually made up a list of all the older units that were equipped with AAR standard trainlines and should have been able to work together in Pacesetter. 

Greetings from Alberta

-an Articulate Malcontent

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Posted by SD70Dude on Monday, May 11, 2020 5:21 PM

Lithonia Operator

On closer inspection, I don't think those sockets are on the cab. They are on boxes (battery boxes?) that are bolted to the railing. So maybe it's for if the engine needs a jump, or needs to give a jump.

The photo is a two-page spread with the article about the New York & Atlantic RR. Great shot.

Here's a photo of a NY&A MP15AC.

https://www.railpictures.net/photo/645371/

The red and black sockets, marked "AAR" and "DUMMY" are what Overmod, Jeff and I have been talking about.  They are indeed for the MU cable. 

The horizontal caps just above the walkway but below the cab windows are where you fill the sandboxes. 

Locomotives do indeed have a standard battery charging port, but I don't see a external one on the NY&A units.  It is commonly placed inside the electrical cabinet.  The connectors are round and are male/female.  They are a couple inches in diameter.

https://www.winconn.com/wp-content/uploads/2016/01/BatteryChargers_V0.pdf

Those round plugs have been in use pretty much ever since passenger cars got electric lighting, I've seen a number of pre-WW1 cars equipped with them.

Greetings from Alberta

-an Articulate Malcontent

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Posted by MMLDelete on Monday, May 11, 2020 11:11 PM

Thanks, guys.

I found some other pix of that type of engine, from different angles, and now I get how things are laid out. I had thought that the boxes (which turn out to be sandboxes) were touching the uprights of the platform's railing. Different pix showed me how that's not the case.

Dude, I think that first pic you linked is from the same photo shoot as the one in Trains.

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Posted by Randy Stahl on Saturday, July 18, 2020 7:30 AM

The AAR has interhange rules on wire specifics so any and all interchange locomotives can be MU'ed with each other. For example pin 1 is slow speed control, pin 2 is MU alarm etc. 

Pin 19 is interesting, on the ATSF they used pin 19 as an additional negative, the Milwaukee used pin 19 as a positive for the MU bell system, they did not MU well.

Pin 4 is the MU negative and pin 13 is the MU positive.

On at least a couple of railroads I worked for they used the MU pins for crap like ditch lights and other stuff with predicatable results. Some people NEVER listen.

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