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.

PECO Insulfrog Description

The PECO Insulfrog is DCC Ready right out of the box! With DCC there is a potential shorting problem as metal wheels go through the frog. This occurs particularly with the Peco Medium and Large Radius Turnouts. On analog/direct current layouts, the Insulfrog was often used for its power routing abilities to isolate a siding. In DCC practice, all track is energized all the time from the power bus. This is where the shorting issue comes in. The momentary short can trip the booster or restart the decoder.

If installing an Insulfrog on a DCC layout, insulated rail joiners on the point rails will solve most of the common issues found with DCC and Insulfrogs. When converting existing trackwork to DCC, follow the instructions presented here to identify and correct any issues which will arise.

As you can see in the table below, the Insulfrog is considered "DCC Ready" as the switch/closure rails are electrically connected to the stock rail nearest to them. Unlike the Electrofrogs the Insulfrog controls the flow of electricity to the routes that come out of the turnout (Power Routing).

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 switch 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.
The usual source of frustration with turnouts and DCC is when the switch rails are electrically bonded together and a metal wheel bridges the gap between the open switch rail and the stock rail. The Insulfrogs switch rails are independent of each other, with the electrical connections made by a tab, as seen in the picture above.

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 at the toe of the frog. Wires beneath the frog carry power from the closure to the point rails. Which point rail is energized is determined by the position of the switch rails which power their closure rails. There is no electrical connection between the stock and point rails outside of the switch rails. On larger numbered turnouts the point rails at the heel of the frog can be bridged by a wheel tread, creating a short circuit.

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

The DCC problem with an Insulfrog is where the two point rails converge at the heel of the frog. A metal wheel can bridge across them and cause a short. Adding insulated rail joiners helps, as per DCC practice all trackage is energized from the power bus, not the switch rails. Meaning the Insulfrog's switch rails are not controlling the point rails.

Insulated rail joiners will also eliminate the possibility of a short between the stock and switch rails, as it would be backfed from the point rails.

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

InsulFrog Modifictions

Once the turnout is installed, making corrections to the installation isn't easy. Prior to installation, installing insulated rail joiners on the point rails will allow the switch rails to control their respective point rail, which eliminates the wheel bridge issue. Cutting and filling gaps with a nonconductive material also works to isolate the point rails from downstream trackwork.

External Links

PECO Technical Page