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In the Peco turnout the switch rails perform both the mechanical action of guiding the train wheels through the turnout and an electrical action of switching power from the stock rail to it's adjacent switch rail. To ensure a good contact a small tab is bonded to the underside of each switch rail which makes a rubbing contact with the underside of it's corresponding stock rail. If you're depedning on these for your electrical switching then make sure they stay clean, i.e. be careful if you paint the rails through the turnout. Additionally traditional ballasting, loose ballast secured with dilute PVA glue, can cause two main problems. Firstly ballast getting under the stock rail and fouling the tabs. Secondly PVA coating the contact surfaces. |
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What happens electrically at the crossing nose (frog)
depends on wether the turnout is Insulfrog or
Electrofrog. The illustration shown here is for an
Electrofrog turnout. The two wing rails (and
closure and switch rails) are electrically bonded to the
crossing nose (frog) and, the Electrofrog being a 'live
frog', to both the point and splice rail. This
means that the selected route electrically sees
continuity with the stock rails and the opposing route
sees a short circuit. For an Insulfrog turnout each
wing rail is individually bonded to the point or splice
rail corresponding to it's route. The bonding is
insulated so as to avoid a short circuit between the two
wing rails. This results in the selected route
seeing continuity as for the Electrofrog but the opposing
route has one rail isolated, instead of seeing a short
circuit.
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Rather than bending the rails as in the
prototype Peco have pivoted the switch rails. These
pivots are another place to take care with ballast. I
have had problems with turnouts where capillary action has
drawn the PVA glue up into the gap between the switch and
closure rails. These required some careful attention
with a dental probe to restore a free action. Looking at the underside of the turnout just forward of the pivots there are holes and slots suggesting an alternative bonding arrangement was considered as per Allen Gartner's DCC turnout wiring guide, i.e. switch and closure rail bonded to adjacent stock rail. |
