Sidings show reading of 3.5 volts when switched off.

First confirm how you are measuring the track voltage. If you are using a high impedance digital meter and do not have a load (like a lighted car or engine) on the siding, then the meter may well read some voltage thru leakage in the track, switch or otherwise. Put a load on the track and then read the voltage. See what you get...it should show zero if conditions are as I mentioned above.

Residual voltage from caps bleeding down possibly?

Chuck,

Thanks for the quick reply. You are right. I am using a digital meter, and the voltage went to 0 when I put a lighted car on the siding.

willygee posted:

Residual voltage from caps bleeding down possibly?

Nope, a typical multi-meter set on AC will indicate significant voltage just because of stray capacitance.  A little bit of capacitive coupling through the switch and you can get impressive readings on a dead track.

Gunrunnerjohn,

I had to look up capacitive coupling, but I think I get the general idea. It sounds like the impedance of the digital meter increases the noise voltage.

No, not quite. The capacitance coupling is a high impedance but the meter is a higher one. So the capacity passes some AC voltage to the siding and the meter can read the voltage with out shorting it out because it has a really high impedance to read with. When the load (car) is placed on the siding it loads the leakage voltage down to about zero.

If you had an old analog meter (much much lower impedance) you would have read zero the first time and this thread wouldn't have happened. Instruments can be quite deceiving if you don't have the experience of years of being deceived by them. ��

cjack posted:

Instruments can be quite deceiving if you don't have the experience of years of being deceived by them. ��

No, say it ain't so.  Test equipment readings deceiving? Never happens! (says me who been fixing electronic stuff since 10 years old).  Amazing how all that book learning goes out the window when real world meets and learn from mentors how things are and how to get instruments to yield real data, especially the world of UHF and microwaves where components take on capacitance and inductance that have to be factored in.  But I digress.

Quoting a recent ad on tv, "We know a thing or two because we've seen a thing or two!"