Frog Types


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Insulfrog, Electrofrog and Livefrog Explanations!

A turnout may be described as a Point or Switch.  

This section is not intended for anyone wishing to construct turnouts from components or kits, it is intended to explain the terminology of a turnout with particular reference to all track supplied by Peco . It will also explain the difference between Peco Insulfrog and Electrofrog turnouts and how to alter the Peco Electrofrog turnouts to Livefrog turnouts and the benefit of doing so. The following image shows the basic terminology that will be used to describe a Peco turnout. The image after the descriptions shows the frog area of the turnout in more detail and shows the components not described on the image below.

Turnout Terminology - some essential information is contained within these definitions:

  1. Toe - The description of the shape of a turnout is taken from a foot. The toe end being the single road input into the turnout, and the heel the exit route which can be either two or three road if a standard or three way turnout. The assumed place for track feeds is from the 'toe end'. The toe end we have two stock rails - the two fixed rails that extend the full length of the turnout.

  2. Stock Rails - The outer continuous fixed rails extending from the toe to the heel. On Peco turnouts they have a machined rebate in the upper profile of the rail to allow the switch rails to locate tightly onto the stock rail.

  3. Tie Bar - The moving bar attached to the switch rails which moves from side to side when the turnout is operated by hand or mechanical means. On a Peco turnout the tie bar is plastic and is controlled by an over centre spring to lock the tie bar against the stock rail for running and electrical continuity. The tie bar has a central hole and two outer spigots to allow alternate connection of a turnout motor. The switch rails attach on more recent turnouts with a tab on the base of the switch rail locating into a slot on the tie bar. On older Peco turnouts the switch rails attached via a small wrap round metal plate.

  4. Switch rails - The moving rails that switch the direction of the train using the tie bar and the switch rail pivot. The switch rails taper towards the toe end to form a 'blade' allowing them to fit tight against the stock rail into a machined rebate. When a switch rail is not in use a gap is present between the switch rail and the stock rail to allow a wheel to pass through. On both insulfrog and electrofog Peco turnouts the switch rails also act as an electrical switch. The contact between the switch rail and the stock rail is essential to pass the power through the frog. If any dirt or obstruction accumulates on the back of the switch rail blade or in the stock rail rebate, the running quality and electrical continuity will be reduced. This may be why you have to push the tie bar when a locomotive stops on a turnout.

  5. Switch Rail Pivot - Located at the end of the switch rail before the fixed closure rail extends to the frog/vee via the acute crossing (closure rail and acute crossing not shown on the above diagram for clarity but shown on the image below). The pivot allows a slight rotation of the switch rail as the tie bar moves the switch rail. 

  6. Frog/Vee - As the switch rails extend towards the exit route of the turnout they become diverging closure rails. One route has to cross the other via the acute crossing which features a small gap to allow a wheel to pass through. Once this gap is crossed the frog or vee is found allowing the final divergence of routes.

  7. Check Rails/Wing Rails - Not shown on the above diagram for clarity but shown on the image below, the check rail pulls the wheel towards the stock rail ensuring the correct road is taken and preventing derailments. The check rail location is critical as it has to pull the wheel before the acute crossing is reached as the gap in the rails at this position is sufficiently large enough to allow the wheel to drift either side of the frog/vee. The wing rails work with the check rails once the wheel has passed through the acute crossing to ensure the correct road is taken.

Insulfrog/Electrofrog Comparison

The following image shows the frog area of both an insulfrog and electrofrog Peco turnout. They are easy to tell apart by looking at the acute crossing and frog/vee. The insulfrog turnout has plastic sections in both the acute crossing and frog making the two frog rails that form the V electrically insulated, as compared to the electrofrog which is all metal and therefore the two frog rails are not insulated. The continuous metal on the electrofrog turnouts makes it much more reliable in operation as the locomotive wheel used to collect the power from the track rarely looses contact with a conductive rail ensuring high quality running.

If you are still unsure turn the item over and look at the wiring on the underside of the frog. The insulfrog turnout will have the wiring crossing over from just before the acute crossing to the frog rail as shown in the diagram below, or on modern turnouts the crossing does not occur but the wires are separately routed to and from the same places to effect a crossover bridge. Electrofrog turnouts have one continuous wire between the closure rails and the frog. This may be as illustrated in the diagram, or as an extended 'U'.

To appreciate the benefits of electrofrog turnouts it is important to understand how both the insulfrog and electrofrog turnouts work electrically. 


This insulfrog description also applies to Peco and Hornby Setrack turnouts as they are unavailable as electrofrog. With power fed from the toe end the stock rails will always remain live. With the switch rail in contact with the stock rail the closure rail becomes live and using the 'crossover bridge' the correct frog rail is powered. As the frog rails are insulated, only one side of the V will be powered. Where the switch rail is not in contact with the stock rail no power will be present and therefore one rail of the V will always be electrically switched off allowing a locomotive to stand on this track as it electrically off. Hence the tie bar acts as an electrical switch using the switch rail to pick up the power from one of the stock rails. This is also why the back of the switch rail blade and the stock rail get dirty as they suffer a small electrical arc each time the turnout changes which causes a small dirt spot to develop.


Again assuming power has been applied from the toe end, the electrofrog turnout works the same as the insulfrog turnout with the switch rail collecting the power from the stock rail but this is where the similarity ends. Once the switch rail is live, it  passes the power to the closure rail which is bonded to the V and opposing closure rail making all rails live to one polarity except the opposing stock rail. The image below shows the electrical working of an electrofrog turnout in both positions. The diagram also illustrates two possible issues with electrofrog turnouts:

  1. The frog rails change electrical state as the turnout changes from straight to branch. If these rails are not protected by insulated (plastic) rail joiners/fishplates it is likely they will cause a short circuit.

  2. If metal stock wheels are not accurate it is possible they may cause a short circuit as they pass through the toe end of the turnout as trailing unused switch rail is close to the opposing polarity stock rail. This can be a particular problem on DCC layouts as a short circuit may cause the unit to overload or cause 'run offs'.

LIVEFROG - Why alter a brand new turnout?

Peco electrofrog turnouts can be altered to work in a similar manner to a hand made turnout achieving the best possible running for a little extra effort. The alterations required are shown below:

The small red lines represent a bridge wire soldered between the stock rail and its respective closure rail after the switch rail pivot about one third of the distance from the acute crossing. This may require the removal of some of the plastic web from the back of the turnout. It is sometimes possible to solder the wire between the two web mouldings on some turnouts. The easiest material to use is 20swg tinned copper wire.

The small blue lines represent a cut in the closure rails about two thirds of the distance from the switch rail pivot to the acute crossing. This cut isolates the frog and acute crossing from the closure rails preventing a short circuit from the wires inserted above. This cut may not be necessary on some Peco turnouts (selected items within the OO gauge code 75 Finescale range) as Peco have inbuilt a small plastic section as part of the closure rail. Out of the box this plastic isolator is bridged by a short length of tinned wire on the underside. Carefully remove with a scalpel or craft knife. 

The green lines show a new area created by the cuts in the closure rails and the insertion of plastic insulated rail joiners/fishplates on the two frog rails marked in yellow. The area is now electrically isolated from the rest of the turnout and will need an electrical switch to change the polarity to match the route selected through the turnout i.e. the polarity of the frog must be the same as the switch rail feeding it. This switching is shown in a later diagram.

What are the benefits of this alteration?

  1. By soldering the stock rail to its respective closure rail (and cutting the closure rail nearer the acute crossing) we have created a safe permanent link between the two rails removing the reliance upon the contact between the switch rail and stock rail for electrical continuity. As the stock rail and switch rail now share the same electrical polarity, dirt in the stock rail rebate or on the back of the switch rail blade make no difference to the turnout operation and no more electrical arc. The familiar requirement to push the tie bar particularly on older turnouts as the over centre spring deteriorates disappears. How many times have you seen that at exhibitions? 

  2. We now have adjacent switch rails and stock rails permanently of the same polarity. No chance of a short circuit on DC or DCC layouts

The diagram below shows the operation of the new livefrog turnout when working with an electrical switch to change the frog polarity as the tie bar moves. The two detailed benefits above are clearly illustrated.

How do we switch the frog polarity?

Switching the frog polarity requires a simple SPDT (single pole double throw) switch connected to the stock rails as the inputs, and the frog as the output - a SPDT switch will always have three contacts where two input contacts always switch to one output contact (or in reverse one input can select two outputs). This can be a standard toggle switch requiring the user to change the toggle switch after the tie bar has moved, or automated into the movement of the tie bar by a microswitch, or more frequently by a switch attached to the point motor e.g. Peco PL-13. The diagram below shows this simple wiring. With the turnout set straight, the frog will polarise with the polarity of the red stock rail - shown by the black link between the red switch input and the green switch output. If you get it wrong (assuming you have the correct output contact) just changeover the red and blue wires.

Is this extra effort worthwhile?

Without doubt! You will see a vast improvement in the performance and reliability of your layout. It may be a little complex but you will have the running quality of the better exhibition layouts constructed with hand made track. Professional Layout Services will always recommend you have this conversion completed where possible on layouts we construct, or when we lay track for clients. Especially recommended for DCC users!


When planning a layout it is wise to check the standard of your rolling stock wheels if you intend to use slips or crossings particularly where finer scale track is to be used. If back to back wheel measurements are not accurate, or if the wheel has a wide tread it may cause short circuits on slips and crossings. This will be a problem with both DC and DCC control.


All electrofrog crossings need some form of polarity switching on the frog or V to ensure the correct setting when a locomotive runs across. The scissors is exactly the same as it has a crossing between four turnouts. In analogue use and with some digital users a switch or relay is used to change the crossing frog polarity. DCC users can simply install an auto reverse module to automatically change the polarity as the locomotive enters the crossing. Ensure the crossing is insulated correctly on the frog rails and if it connects to other turnouts as required; then simply connect the outer crossing stock rails to the DCC ring main together with the auto reverse module inputs, then connect the module outputs to the crossing frogs - one to each frog. No need for complex wiring, switches or relays!


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