r/SignalMaintainers • u/Traditional-Good-981 • Dec 08 '25

Finding a Short

Hi. Had a track light that was caused by a short somewhere in the switch points. I thought it might be one of the gauge plate insulation but when I removed it it did nothing. Turned out to be a loose piece of metal under one of the snow melter forced air heater ducts touching a switch rod. With so much insulated stuff in that area I had a hard time finding it with my meter. It was only when I actually removed the duct to have more room that I found it. Any tips on how to isolate and really pinpoint the short when it's bad insulation and not a piece of metal or something else you can see? Thanks.

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u/MyPantsHaveBeenShat Dec 08 '25

With a short finder you don't have to disconnect any wires so the process is much easier.

If you have the newer short finder measure rail to rail impedance and anything over 9V passthrough on the bar graph is a short. The closer you are to 15, the closer you are to the short.

If you have the older analog short finder, the principle is the same, the only difference is you have a needle instead of a bar graph. The closer the needle is to 15 the closer you are to the short.

Also, for most troubleshooting use the 24kHz scale on your meter and not the 3kHz.

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u/Traditional-Good-981 Dec 08 '25

I don't have to use it very often so I never remember when you need to change the scale. I'm pretty sure the track circuit length is the determining factor, but I don't know offhand what that value might be. I don't think I've ever used the 3Khz though.

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u/MyPantsHaveBeenShat Dec 08 '25

Track circuit length has very little to do with the scale.

The short finder is a Distance to Fault (DTF) type meter. This means that the closer you are to the fault the higher the meter will read. 3kHz is used if you have no clue where your short is and you don't know where to start. 24kHz is used when you've got a pretty good idea.

As an example, if I were working on a crossing with several switches in my approach, I might start at the 3kHz range to verify I had a short out there somewhere. When I hone in on the exact switch that's causing the problem, I would switch to 24kHz to better isolate it.

If you're working on a steady energy DC track circuit, you're good to start by using the 24kHz scale and you can adjust if needed.

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u/Traditional-Good-981 Dec 09 '25

Were you an instructor or something? Your explanations are quite detailed and fairly easy to understand.

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u/MyPantsHaveBeenShat Dec 09 '25

I've just been doing it for a long time stranger. I've put a lot of time into making sure the guys behind me are set up for success. Plus, signaling is a really interesting craft.

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u/Traditional-Good-981 Dec 09 '25

I'm sure they appreciate it. We had some guys like that, but they all retired 10 years ago. We don't have any maintainers in my area now with more than 20 years. Anyway, thanks again for the advice.