Why do we often hear that we should attach drops every three feet or better yet, to each and every piece of track and each turnout? What could happen if we disregard the experts and just attach our power at one spot and allow the track to carry the current around the layout? People that try it find that it can work quite well – for awhile. What are we missing?
01. Rail joiners and rails are made of dissimilar metals. This is never a good thing over time. Corrosion can creep in and eventually the electrical connection can fail.
02. The electrical conductivity of track is far inferior to that of a proper-sized copper bus wire. The resistance of track or smaller gauge wire can introduce so much resistance that the power pack circuit breaker does not recognize a short circuit as a short and will not trip. This can result in melted wheels and/or burned out electronics. Yeah, you say. That cannot happen. WRONG! I know of one model railroader that had several meltdowns when locomotives shorted out on a turnout far from his booster. We added four DCC Specialties PSX-Series circuit breakers, he broke up his bus into 4 runs and he ran a new 10 gauge bus wire to the distant section, replacing a 14 or 12 gauge bus. The result: No more melted wheels.
(DCC) RESISTANCE & VOLTAGE DROP for Wire & Track
CONDUCTOR RESISTANCE @ Voltage Drop Voltage Drop
1 Ft. (Paired) @ 10kHz (DCC) @ 1 Amp @ 3 Amps
#24 Stranded 0.0276 0.051 0.153
#22 Stranded 0.0173 0.032 0.096
#20 Stranded 0.0106 0.021 0.064
#18 Stranded 0.0048 0.010 0.029
#16 Stranded 0.0060 0.012 0.036
(low Cu content)
#14 Stranded 0.0027 0.005 0.016
#12 Stranded 0.0018 0.003 0.010
#14 Solid 0.0028 0.006 0.017
# 12 Solid 0.0019 0.004 0.011
#10 Solid 0.0013 0.003 0.008
Code 55 Ni-Ag trk. 0.1107 0.222 0.664
Code 70 Ni-Ag trk. 0.0757 0.151 0.454
Code 83 Ni-Ag trk. 0.0424 0.085 0.255
Code 100 Ni-Ag trk. 0.0275 0.055 0.165
I = E/R *or * Amps = Voltage / Resistance
Material Resistance/Ft Track resistance vs. copper wire
Code 55 track 0.1107 Ohms Track resistance is
Stranded #12 wire 0.0018 Ohms 0.1107 / 0.0018 = 61.5 greater **
** This is why we use a heavy main power bus with many drops!
- Try to keep power bus runs below 30 feet in length.
- Be consistent with your wire color-code.
Model Train Operations 