Solenoid Devices

SolenoidA coil of wire which, when an electric current is passed through it, causes magnetic attraction.

There are three groups of devices in Z-Scale that use solenoids for operation; remote track switches, remote uncouplers and relays. The notion of “remote” is one of the great advances in model railroading.  With remote control, you can operate devices from a distance, and it is possible to remotely control these devices from two different locations, or more. In short, remote control adds fun to the model railroad hobby.

Track Switches (Turnouts)

Probably the first improvement in model railroading was the creation of the remote turnout.  With this remote operation, you could direct a train to go in two different directions without walking around to throw the turnout by hand.  (Note that we use the word “turnout” to describe the track switch to avoid confusion with electrical switches, which are also present on model railroads).

The turnout has one moving part, the points; these are the moveable rails which guide trains in one direction or the other.  In a manual turnout, you simply move a lever to move the points. With a remote turnout, you can also throw the points with electricity.

Here is a diagram of the wiring connections for a turnout:

The yellow wire provides power to the two solenoids of the turnout. Internally, the yellow wire is connected to one end of each solenoid coil of the turnout.  At the other end of each coil, a blue wire is connected that is then connected to the control box (note the 7072 is an earlier generation of the momentary control box for such devices). At the control box, a gray wire is connected to the transformer. When operated, a button is pressed on the control box and electricity flows through the coil, pushing a slug of metal into the opposite coil. This slug of metal has a linkage to the turnout points, which results in the points being moved to the opposite position.

Although different in appearance, the double slip switch is operated in the same fashion. Likewise, curved turnouts also are operated similarly.


The uncoupler is another remotely operated device.  When operated, the uncoupler raises a gray plastic ramp with teeth that disengage the couplers between two cars.

The 8587 uncoupler is wired in the same fashion as the turnout, but because it has only one solenoid, many modelers connect both buttons on the control box so that pushing either button will operate the uncoupler.  The thrifty among us often use the pair of buttons to control two uncouplers, but I always have trouble keeping straight which button controlled which uncoupler.


Relays are another interesting remote operation device. These devices have electrical contacts which are switched instead of having track points which are moved. The 8945 Relay is Märklin’s basic relay.

   Internally, the 8945 looks like this:

   At the top are the two solenoid coils, each with a common yellow connection and each with their own blue wire connection, one with a red plug and one with a green plug.  At the lower edge of the relay are a series of electrical contacts. The left connection is “either/or”.  When the relay is in one position, the two right pairs of connection points are “open” or “off”. When the green coil of the relay is activated, the two right hand connections are “closed” or “on”. The 8945 relay can be operated by hand, using the lever on the top of the case, or momentary electrical contact will operate the coils.

More about using relays for automatic operation here.

The 8947 Relay is a special application relay used primarily for controlling return loops.  With two-rail DC trains, a problem occurs when a track loops back upon itself:

The 8947 Relay provides an automated way to handle train movement through such a reverse loop.

   Internally, the 8947 looks like this:

At the top are the two solenoid coils, each with a common yellow connection and each with their own blue wire connection, one with a red plug and one with a green plug.  At the lower edge of the relay are two pairs of electrical contacts. In the “red” position, the contacts 1 & 4 and 3 & 2 are connected. When the relay is in the “green” position, contacts 1 & 3 and 2 & 4 are connected. Details of this operation are here.

While not a solenoid device, the 8946 Manual Signal Controller operates in a similar fashion to the 8945. Internally, it has the same electrical contact arrangement but only has a manual switch for operation.

   More about the 8946 here.

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