Page 31 - B2B 1 to 7

An alternative is to solder to the web of the rail on the outside of the track. Careful filing and a little paint can make it near invisible.
Points
In a point, the switch rail and its associated closure rail provides a connection from one running rail to the other and as everyone knows this means short circuits. To avoid this gaps or insulated joints are required. With commercial points this has usually been taken care of but it is as well to understand what is going on.
The wiring of points is quite simple but just needs to be carefully considered. Points come in two basic flavours – those with a solid metal frog (often termed an “Electrofrog”) and those with either a plastic frog or where there is insulation between the frog rails (the “Insulfrog”).
Power beyond the point no longer relies on a good contact between switch blade and stock rail.
To achieve this arrangement a gap is needed between the switch rail and closure rail. On a commercial point this is done by removing pre- fitted wires. The wires between the switch blades and frog should be removed and the switch rail wired to its stock rail. This avoids relying on the switch rail/stock rail contact and prevents any shorting between switch and stock rail via the wheels as both are always at the same polarity.
An alternative to switching the polarity of the frog available in DCC is the “frog juicer”. When a wheel bridges a gap in the points that causes a short circuit, this device very quickly reverses the polarity of the frog so as to remove the short circuit. These are not available for d.c. layouts.
Now let us consider the “Insulfrog”
In the “Insulfrog” version, the 4 rails converging on the frog are insulated from each other. The four rails can be connected up in a number of ways. One method is to wire all 4 rails together to make it the same as an “Electrofrog”. This would mean either relying on the switch blades for contact or introducing a switch.
The other way to wire it is as shown below.
A B
This arrangement avoids the possible short circuit to the back of the wheel and avoids the need to provide a switch to switch the power. For D.C. users, one possible disadvantage is that moving the points against a train does not remove power from it (Locos A and B both receive power). For DCC this is a benefit in that it keeps power to all parts of the track.
Construction of the insulated frog must be such that wheels cannot bridge the insulation at any point so as to short opposite polarities together.
Diamond Crossings
A crossing with electrofrogs requires some switching. If a train is travelling East-West over the crossing below, the rail polarities must be as shown. If however the move is North-South, then the polarities need to be different.
The Insulfrog version is much simpler in that there is no need to change polarities. However, the angles involved on a diamond can be larger than on a point so clearances can be eroded. There have been instances of shorts due to wheels bridging the insulation in the crossing.
For Electrofrog crossings, the North East and South West corners do not change polarity but the North West and South East corners need to be switched. There are a number of ways of doing this but a two
Firstly we will consider the “Electrofrog”.
X
A
B
The simplest arrangement is shown above. To receive power, a loco needs one polarity on one rail (e.g. red) and the other polarity on the other rail (e.g. blue). Locomotive A receives power but Locomotive B does not as both rails are at the same polarity.
Whilst this arrangement is simple, it has some drawbacks. The main problem is that the power to Loco A and the track beyond, the point relies on a good contact between the switch rail and stock rail at point “X”.
Another possible problem is that if the switch opening is at scale openings, there is a chance of the back of the wheel shorting as shown below because the stock rail and switch rail are at opposite polarities.
Short
An alternative is to switch the polarity of the frog.
A B
A
The switch is linked to the movement of the points. This could be a contact on the point motor or a slider-switch used to move the point. The contacts of the switch are used to change the polarity on the frog.
B