As has been reported a few times here on the forum, some people have had electrical conductivity problems with Lionel's 6-81248 and #2025050 and FasTrack Girder Bridges new out of the box. When a bridge is fitted to regular FasTrack, the result is that trains may stop on the bridge. This post is not intended as a critique, but rather to be informative and provide information and some possible solutions.
Since the reasons for the problems with this bridge discussed here on the forum thus far have been inconclusive, I decided to buy a new 6-81248 at a Local Hobby Shop and investigate. I believe the #2025050 Christmas version is likely made of similar construction materials and this post may apply to it as well.
After checking it out for myself, I owe an apology for previously passing along some misinformation I'd read here on the forum in an old post. I have gone back and edited my old replies that were in error and intend to reply with corrections elsewhere as appropriate. More on that is explained below under the Apology/Explanation heading.
If you're reading this and just want to get to the part with some fixes, please see the Solutions heading.
Bridge Construction
The bridge's 3 tab rails appear to be made on a different set of machines (including the forming dies) than normal 10” FasTrack 4 tab rails. In addition to the different number of tabs to secure the rails to the roadbed/bridge, the rails also have a different end profile. When comparing their ends, the bridge rails are round on top and regular FasTrack rails have a flatter top. The dies used to form the bridge rails also seem to have a greater tolerance.
The mating pins were so loose inside the bridge rails that there was an average 8 thousandths of an inch gap on both sides between the pins and rails. Pins measured 0.0975in. at their widest and inside width of rails measured 0.1135in. just below the crown. This may sound like a small gap, but for low voltage, it's enough to prevent current flow.
This video demonstrates how loose the pins were when new out of the box.
TESTING
Also before the first use, there was also no electrical conductivity between the track pins and the bridge rails while still disconnected from the other track (infinite Ohms on two different known good test meters; both analog and digital on their highest ranges).
When I connected the bridge to some known good straight FasTrack sections, there was no electrical conductivity from the normal straight sections to any of the 3 corresponding rails on the girder bridge.
All of this explains why there is poor or no electrical conductivity through the bridge and why trains stop on it.
APOLOGY/EXPLANATION
I apologize for replying in a previous thread by repeating some (unbeknownst to me at the time) misinformation about these Girder Bridges. I had read in an old OGR forum topic on this subject that someone had identified the bridge's rails as being made from aluminum. The dull matte surface of the rails, the fact that they have a different rail profile, their historically poor conductivity, and different number of folded tabs underneath all tended to make that assertion somewhat believable. Maybe it was true at one time, maybe not.
At the time, not having one of my own to verify this aluminum assertion, I repeated it with the intent of offering some solutions to the “train stops on bridge” issue. Now that I do have one, I can say definitively that THE RAILS ARE DEFINITELY NOT MADE OF ALUMINUM! They're attracted to a magnetic field and the metal they're made from is harder, like steel. I'm sorry for any inconvenience my erroneous reply may have caused.
SOLUTIONS
If you're wanting a quick pseudo-fix without soldering, the rails on the girder bridge could be squeezed with pliers to tighten them around the mating pins, but this might be a temporary fix at best and would likely create a noticeable bump at the rail joint entering the Girder Bridge section because of its unique rounded top rail profile and comparatively oversize dimensions.
My recommendation is to solder feeder wires to the bottom of the bridge rails which either connect to the track power bus or connect to adjacent track pieces which already have good conductivity to the track power bus. Here's how I did it.
Using a surplus 16 gauge power cord from my parts bin, I cut two 22” pairs of feeders (long enough to reach further than the closet track piece if needed) plus a third single wire jumper to go between the two outside rails. After stripping 1/4” from the ends of each, I tinned the bare wire ends and soldered them onto the rail tabs underneath the bridge.
Next I attached Faston connectors to the 4 ends of the feeders. Those connectors plug into the tabs underneath most regular FasTrack sections.
After everything was connected like this, there was no measurable resistance on each of the rails from end to end.
Testing also reveals that a train traveling across the bridge now has no electrical issues.
I hope this post helps anyone who may have experienced issues with or is planning to use a FasTrack Girder Bride on their layout.
SteveH
Also, per your other thread, so glad to see you will soon be working on solving some of your own problems on a layout of your own, as well as doing such an excellent job on helping the rest of us.
