Having 2 cables on each side means that you don't have to have the cars all oriented a certain way and plus it has a measure of redundancy. If there is a problem on one side, you can short-loop the bad side and still power the cars to the rear. You can't do that with just two runs of cable.

Good point. It does almost seem like the standard writes itself. But, again, someone had to choose the connectors and actually do this for the first time.

filmteknik,

I think what you are looking for is who created the C&NW plan for 480VAC HEP. By default, the plan became a C&NW standard, but it certainly wasn't used by the industry yet. At this time, what industry-wide standards existed were maintained by the American Association of Railroads (AAR), and I am not aware of them touching the issue of HEP.

Amtrak first use of 480VAC occurred with their purchase of intercity bi-levels from the C&NW. At first they leased C&NW F-units to power these cars and later rebuilt some ex-PRR E-units with HEP generators. As Amtrak refined the system commuter agencies tended followed their specifications when ordering or rebuilding equipment. In the past decade (or so) The American Public Transportation Association's Passenger Rail Equipment Safety Standards have updated much of what existed as company specific plans/standards or standards that were last updated by the AAR before Amtrak.

I still think looking for the patents is your best bet for the question about the connectors - and IRM is a great place to start the research. I you can post here the patent numbers you find I (and others I'm sure) would be interested in helping you research it further.

Regarding the connectors, I'll offer an additional hypothesis. They may have been originally designed for marine shore-power - but proved to be readily available when the C&NW was looking for a HEP alternative.

Thomas Cornillie

There are 3 additional pins besides the big power pins - a sense wire and two grounds. The sense pin is shorter than the other pins so it 'makes' last. The grounds are simply to give a reference for ground-fault detection.

The locomotive puts a signal on the "sense" pin of connector 1 and expects to see that signal come back on the "sense" pin of connector 2. At the end of the train, each side does a "loop back", the HEP cable from connector 1 is connected to connector 2. Same thing for 3 and 4. Think about what this means: nowhere on the train will you find an unattached cable or connector that might allow curious fingers to find 480vac.

This protection is bulletproof: If a curious hand unplugged an HEP cable, that would disconnect the sense wire even before he got the connector halfway out, which would trip the HEP.

It is possible to "short loop" one side of the HEP, so connectors 1 and 2 run the length of the train while 3 and 4 do their loopback somewhere in the middle.

What does that do to "curious fingers" protection? If every car is wired so that the 1-and-2 bus is isolated from 3-and-4, then no problem. The sense wire will not detect connectors 3 and 4 being loose and exposed, but there wouldn't be any power on them either. However each car would need a switch to decide which side it draws, and staff would need to actively manage this to avoid overcurrent on one side. However, if all 4 buses were wired together in ANY car behind the short loop, then cars behind the short loop would be "lighting up" side 3-4 without "curious fingers" protection. That latter way is how Amtrak operates.

Obviously you know the last car has power; so you know at least one side is wired continuous to the back. However that doesn't tell you which side, and one side could be short-looped while having dangling connectors behind it. Only a 2-side walking inspection can tell you this.

I could foresee adding a data link as a modulation on top of the sense wire, to allow microcontrollers in the cars to chat with locomotive and network* about such topics. Add a magnet, wait, RFID to each connector and inductor to each socket, and the onboard computer could get a very complete picture and propagate that for long term diagnostic purposes.

Yeah, I know about the safety circuit; I just didn't know they were sending a ground along the way.

VIA uses / can use the two sides separately. I presume cars wired to their standards do have switches to decide which side to tap. But USA cars (I presume) all four cable sets are commoned at the car junction box.

If that is the case I recall seeing an error on an FRA document regarding the policies on short looping when the need arises. As I recall the document stated that all current will be concentrated on one side after a short loop. If I understand things correctly, that is not true. The current would be concentrated to one side only from the junction box before the short loop until the junction box after the short loop but from that point to the rear of the train, it would once again be handled by all four buses.

Thomas, did C&NW go HEP before CB&Q? C&NW's bilevels were built as steam & battery as were the Q's. If so then they might be the ones, phase order differences not withstanding.

PS: We met once years ago aboard an IRM RPO.

You are understanding correctly.

The short-looping method has another method besides the normal method, only to be used when you can not locate exactly where the problem is: short-loop 1&2 on the rear of the locomotive, and short-loop 3&4 on the rear of the 1st car, using the common bus to energize 1&2 behind the short-loop on that side.

This is one benefit to the arrangement with the car's HEP trainlines connected together. In the event of severe problems keeping everything together, you can short-loop as above for the purpose of getting the train to it's destination with power.

From the rear of the 2nd car, power will be on all 4. Clever.

Why don't they just have a safety circuit override switch (something you have to break the seal on)? No more dangerous since any short loop creates the condition that cables and connectors could be accessible while live. At least with an override switch there's the possibility that the problem you're addressing is with the safety circuit itself and full ampacity is preserved.

Because it would not be long before the attendant went right for the override because checking the train takes too long, and who cares that one of the cables is danging with no plug and just nakkid wires hanging out.

What "standardization" there is in HEP ends at the TLC circuit. A quick look through the locomotive wiring schematics within reach showed the following TLC control circuit variations among major passenger operators:

Pin 1 TLC circuit, Pin 2 and Pin 3 go to ground connection at HEP cabinet
Pin 1 TLC circuit, Pin 2 and Pin 3 go through the unit end to end with no connections
Pin 1 or Pin 3 TLC circuit, selectable by position of the TCM switch
Pin 1 plus Pin 3 TLC circuit, with the two pins wired in parallel at each receptacle
Pin 1 plus Pin 2 plus Pin 3 TLC circuit with the three pins wired in parallel at each receptacle

And a look at several schematics from one agency shows their TLC circuit arrangement changed over the years, they were originally wired with TLC on Pin 1, and now are wired with TLC on Pins 1, 2, and 3 in parallel.

PC

Because that's the easy way, and with the short-looping methods, even the last-resort one I listed, you have walked the train at least twice, on both sides, and if you are short-looping, you take every precaution to ensure the cables behind the short-loop are secured and not dangling free.

A button, even with a seal, is a simple way out of fixing the problem, and crews will just push the button and go rather than getting down and diagnosing the problem and putting eyes on the cables and connectors.

FRA's policy on short looping:

http://www.fra.dot.gov/eLib/Find#p1_z10 ... _s35_kloop

If this does not work, go to http://www.fra.dot.gov/Page/P0044 click on Technical Bulletins in the right hand column and search on "loop" or "98-38"

Steve

Yup...and there again is the error in point 2. The double current thing exists only from the junction box of the car before the short loop until the junction box of the car after the short loop after which the current is redistributed to all four buses.

Furthermore, as long as there are less than 8 cars behind the short-loop, you will not exceed the current rating per cable pair. Once you get 8 or more cars behind the short loop, you are supposed to start limiting current draw in the cars behind the short loop.

That choke point is the ruling factor in what the cars behind it may draw. Pull more than 50% of 4-cable rating and you start thermally stressing things in that connection. Weakest link in the chain and all that. Even worse, if one of those phase connections is marginal, it's now sharing the work with only 1 other path instead of 3.

Of course, having the full width pipe behind the choke point will ease resistive losses somewhat, but that's a footnote and would have happened anyway.


That depends on if one is a diner. Different cars have different loads.