Peco Insulfrog

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Part of a series on turnouts or track switches and Digital Command Control

Digital Command Control: Turnouts - PECO Insulfrog

Thanks to Railway Bob for the information and permission to use it.

Also see the PECO Electrofrog page.

If you have problems with a particular locomotive or rolling stock (equipped with metal wheels) causing shorts when travelling through a turnout, you should begin by checking the wheel gauge using an NMRA guage appropriate for your scale.
A PECO Insulfrog. Note the tabs on the switch rails, which control power routing.
The Peco Insulfog functions just like an electrical switch: Tabs under the point rails route power to a closure rail, under the frog, then to the correct point rail. A spring under the cover above the throw rod keeps the switch rails in position.

Insulfrog Description

The Peco Insulfrog is DCC Ready right out of the box! There is a potential shorting problem as metal wheels go through the frog. This occurs particularly with the Peco Medium and Large Radius Turnouts.

As you can see in the table below, the switch is considered "DCC Ready" as the point/closure rails are electrically connected to the stock rail nearest to them. Unlike the Electrofrogs it does not control the flow of electricity to the routes that come out of the switch.

The usual source of frustration with switches and DCC is when the point/closure rails are electrically bonded together and a metal wheel bridges the gap between the open point and the stock rail.
PowerRoutingInsulfrog.jpg


Details of the PECO Insulfrog
The frog is cast plastic, so it is non-conductive. The metal guard rails are also unpowered. Note that gap filled with plastic on the left isolating the closure rails from the wing rails. Wires beneath the frog carry power from the closure to the point rails.


As shown in the pictures, the diverging rails are powered using small wires which bond the appropriate rails together.

The usual problem with an Insulfrog is the point where the two point rails meet at the heel of the frog. A metal wheel can bridge across them and cause a short.

These tabs on the underside of the switch rails electrically connect it to the stock rails. Power is then available on that switch rail, and through the closure rail is supplied to the appropriate point rail. This is how the power routing is done.


Wiring on the underside of a Peco Insulfrog connecting the point and closure rails
Power flow across the frog of an Insulfrog


Electrical Issues

Short Circuit Caused by Wheel

NoShort.jpg
Wheelbridging.jpg
PECO-InsulFrog.jpg
As the wheel moves from the mainline or diverging route into the frog and toward the points, the inside diverging rail and the inside mainline rail of the frog get narrower until they terminate in the plastic section of the frog. While this narrowing is not obvious in the photo, it is very obvious with large numbered turnouts. In the diagram, as the locomotive's wheel travels along the inside diverging rail, it begins to overhang the mainline rail. As it gets closer to the point of the frog, the wheel can cross the gap between the energized rails. A short occurs when the wheel bridges both rails and the command station/ booster shuts down.


InsulFrog Modifictions


External Links

PECO Technical Page PECO Home]