SSPRR Run Room

Playing with Toy Trains

Toy Train Layout Wiring - Glossary Plus


Basic Intermediate Advanced Wire Management Bus Wiring 120V Train Room
Glossary Plus Wire Sizes Switches Load Calculations Soldering Troubleshooting

Glossary for Electrical Wiring of O Gauge 3 Rail Toy Trains

  • AIU, DCS Accessory Interface Unit for wireless remote control of turnouts and accessories.
  • Amp, Ampere, unit of electrical current and the measure of heat in a circuit. 10 amps should be the maximum for all O Gauge 3 Rail Toy Train circuits.
  • Amp Meter, measures amps being used by trains or accessories. If there is no load there are no amps.
  • Block, insulated section of a Power District. (example - four switched stub tracks powered through one District would be four blocks within that district)
  • Brick, Fixed voltage ac transformer with no controller.
  • Bus, wire, bar, or strap used to distribute power that is tapped at intervals.
  • Can Motor, runs on DC current. (see "Pulmor and Can Motors" at )
  • Circuit, a. the complete path of an electric current, including the source of the current, intervening resistors, loads, etc. b. any well-defined segment of a complete circuit.
  • Color Code, a system for identifying electrical wires.
  • Common, Outside Rail, U*, ground, black, (-)
  • Components, examples are switches, circuit protection devices.
  • Consist, the cars which make up a train.
  • Continuity, unbroken connection between two points.
  • Conventional or Command Control, Conventional controls trains with track voltage as postwar trains were originally controlled.  Command controls with digital signals sent through track to the engines and operating cars. Track is normally set at 18 volts.
  • Current, the movement or flow of electricity measured in amps (see current types). *
  • District, see Power District.
  • Electromechanical, of or pertaining to mechanical devices or systems electrically actuated, as by a solenoid.
  • Ground, the pole of a toy train transformer to which all lighted, motorized, or magnetic devices may be attached by one of their two wires.  Any other pole of the transformer will provide a predetermined amount of power to these devices in conjunction with the ground (thus the term "common ground").
  • Ground plane, (don't use, too nebulous).
  • Jumper, short conductive connection between two conductive points.
  • Latching Relay, Latching relays have no default position and remain in their last position when the drive current stops flowing.  see also Non-Latching Relay
  • Load, power demanded by devices. (for our purposes amps x volts = watts = power)
  • Lockon, factory made connector for attaching wire to track.
  • Modern era, 1970 to present.
  • Non-Latching Relay , A non-latching relay has an initial position of normally closed (NC) maintained by the force of a spring or permanent magnet while no current flows. The normally open (NO) contact is maintained by the force of a magnetic field while current flows through the coil. When the current stops, the relay reverts back to its initial NC position.
  • O 027 Gauge, trains run on 3 rail track with 1 1/4" between the outside rails. *
  • Parallel Circuit, several devices (such as light bulbs) are connected to both power source taps. **
  • Phase, a particular stage or point of advancement in a cycle.
  • Phase tape, colored electrical tape for identifying electrical wires. **
  • Phase transformers, plug two or more ac transformers into a 120V wall outlet so the low voltage sides are "in phase". **
  • Postwar era, toy trains produced after World War II, 1945 through 1969.
  • Prewar era, toy trains produced before World War II, 1900 through 1942.
  • Power District, track and/or accessory section powered by one transformer output. This District has "variable voltage/center rail" input isolated/insulated from all other "variable voltage/center rail" transformer inputs.
  • Primary, the wires that connect the transformer 120 V winding side to household current (120 V).
  • Relay, an electromagnetic switching device consisting of an armature which is moved by an electromagnet to operate one or more switch contacts.
  • PTC Resettable Fuses, Positive temperature coefficient (PTC) thermistors **
  • Secondary, the wires that connect to the low voltage side of transformer winding (5 - 25 V).
  • Series Circuit, two or more devices (such as light bulbs) are connected one after another. The first device is connected to one power source tap and the last device in the series is connected to the opposite power source tap. **
  • Short Circuit, condition where the electric current by-passes the motor or other device it is supposed to operate and flows to the outside rail/common which is connected via circuit protection to the transformer. When a short circuit occurs the train stops, the lights dim or go out altogether, and the circuit protection breaks the connection. Modern trains and accessories have circuit boards that can be damaged by short circuits. The circuit protection in transformers protects the transformer, not the trains.
  • Solder, alloys fused and applied to the joint between metal objects to unite them without heating the objects to the melting point.
  • Spade lugs, solderless connector tabs.**
  • Switch, a device that connects, disconnects, or redirects the current in a circuit.
  • Tap, wire connected between distribution/bus wire and track or accessory, connect wire between two points.
  • Terminal Strips, multiple screw clamp terminals (best for terminating mixed sizes of wire)
  • Terminate, attach one end of a wire to a point (more than one wire may terminate at one point)
  • Tinned, wires or connector contacts coated with solder.
  • Transformer, 3-Rail O gauge toy train layouts are powered by ac transformers that reduce 120V ac house voltage to 14V to 25V ac voltage. Exception - a few sets and small motorized vehicles are designed for dc voltage. An ac transformer will damage a dc engine or dc motorized vehicle.
  • Tug Test, gently tug wire after connected to confirm connection.
  • Turnout, track assembly for switching a train/car onto a different track.
  • Voltage, electromotive force. 3 Rail O gauge toy trains operate at 25 volts ac or less. Household voltage is 110-120 volts ac.
  • Volt Meter, measures voltage on line or track when voltage is being applied to line or track.
  • Wall Wart, plug in the wall transformer.  see example
* Click for more information
** Click for illustration and more information


Abbreviations and Symbols

  • AKA, also known as
  • U = common
  • V = Voltage
  • vac - alternating current voltage
  • A = Amps
  • ac = alternating current
  • dc = direct current
  • term = terminal

Abbreviations for Switches

  •  sw = switch (not turnout)

  • sp = single pole

  • spst = single pole single throw

  • spdt = single pole double throw

  • dp = double pole

  • dpst = double pole single throw

  • dpdt = double pole double throw

  • NC, electrical contacts Normally Closed.

  • NO, electrical contacts Normally Open.

  • HP, horsepower

  • VAC = volts ac  (alternating current voltage)

Abbreviations for Colors

blk - black rd - red blu - blue brn - brown or - orange yel - yellow
  prp - purple grn - green wht - white gry - grey  


  • V x A = Watts

Light Bulbs

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