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What type of switch is required to control a point motor?

When turnouts are operated by point motors, they require the same forces applied to them as they would do operated by hand, to move the point blades force needs to be applied, but the rest of the time no force is required and the blades sit quite happily in their chosen position. This means that a way is needed to deliver power to point motors in occasional short bursts opposed to a constant live feed and this is where a passing contact switch comes in.
Regardless of which way the switch is set, a passing contact switch emits no constant power feed, instead, it delivers a short burst of power halfway through being thrown. This short burst of power switches the polarity of magnets on the point motor, in turn, switching the point blades.
As is often the case, you may want your switch to control more than one set of points, for example, where there's a crossover or an entire route to be set. This is possible with a single switch, however, you will likely need more energy to be released when the switch sends its burst of power to energise the numerous magnets involved.
An enhanced burst of power can be achieved by installing something called a CDU (Capacitor Discharge Unit) into the circuit between your controller and the switch. A CDU's job is to store up power from your controller's auxiliary port (16v-AC or 12v-DC) and release it all in one go when you throw the switch. A CDU will generate enough power to comfortably operate up to four point motors simultaneously.
Wiring a passing contact switch is relatively simple and a basic understanding of electrics plus a diagram specific to the number of points to be powered will suffice.
Passing contact switches are available with different coloured levers that correspond with the colours that would be used in a real signal box. This is done to add realism and play value to your control panel, so rest assured, the different coloured switches are purely cosmetic and do not affect their operation. If this idea appeals to you, Peco produces a console unit for their switches to fit neatly into and it looks great on a control panel.
A commonly asked question is, are all point motors wired in this way? the answer is no, there are powered motors known as slow action point motors that change slowly for visual effect, but they are seldom used. It's safe to say that 95% of regular solenoid point motors will require operating with a passing contact switch, but as always, the advice is to check with your local model shop to be sure.
Posted in: Model Railway, Power and control

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