Basic track wiring (applies equally to DC and DCC layouts).

How should I connect power to the tracks?

How to route power to your tracks

There are many ways to feed power to your tracks. With classic switched control panels the natural method is to run wires from your throttle(s) to the switches on the control panel and then a wire from each power switch to its associated track section. This naturally uses a lot of wire, and makes lots of thick cable bundles to route around.

An alternative is to run a 'ring main' from each throttle around your layout and then route power as required to each track section with relays. If the wire from each throttle runs around the whole layout and then back to the throttle (if it makes sense in your installation) then you can use thinner wire because current can flow both ways around the loop. The relays are of course controlled from the switches on the control panel, but to save wiring you can use RPC modules, with either a PC or a Merg RPC PTP module to drive the relays from the switch settings. This way you have far less wiring, and if you want to add an extra track you only have to connect an extra relay to the appropriate ring main(s).

I do something different again. I use one remote controlled throttle per track section. It sounds expensive but my QTU (Quad Throttle Unit) module works out quite cheaply. So I put one or more QTUs under each baseboard to feed all the track on that board. I then run a ring main of low voltage AC around the layout to feed all the QTUs. The power output from each QTU feeds everything else on its baseboard such as infra-red sensors, solenoid and slow action turnout motors, lamps. The only long-distance wiring I have is the AC power feed and an RS485 data cable. The only inter-baseboard wiring is for tracks that cross baseboard boundaries.

What wire should I use?

How thick must my wires be?

The volt drop depends upon three parameters:

  1. The current being drawn

  2. The length of the wire

  3. The thickness of the wire

The current varies a little between locos, and a little with speed, but mainly it is the scale you are using that defines current. Some starting point assumptions might look like:

Scale Slow speed Full speed Stalled

Z  80mA   250mA  400mA
N  100mA  300mA  600mA
OO 150mA  400mA  800mA
G  400mA  800mA  1200mA

but these are all approximate and will vary between locos, track and throttles.

You do NOT need to design for stall current, except to ensure that your wires will not melt - do not worry about this even ribbon cable will not melt on a stalled G scale loco.

The length of each run is obviously a function of your particular installation and I cannot give you any guidance at all on this one.

The other variable is obviously the thickness of the wire. Thicker wire costs more, is harder to install and make much bigger bundles. Think carefully before jumping in with wire that is thicker than you really need.

To calculate what thickness of wire you need:

r is the resistivity (in ohms per meter) of the cable you need: r = R/L
eg. 10m cable gives r = 1.25/10 = 0.125 ohms per meter.

Now pick a cable or wire with that resistivity or less.

Solid core

diameter AWG ohms per meter

1/0.52    24    0.094
1/0.55          0.070


wire type ohms per meter
7/0.1    0.055  0.384
7/0.13   0.08   0.227 (ribbon cable)
7/0.2    0.22   0.092 (ribbon cable)
19/0.127 0.25   0.0836
19/0.15  0.35   0.0561
19/0.19  0.5    0.0401
19/0.25  0.933  0.0212

I use ribbon cable on N scale and so I need 300mA and my runs are typically 6m.

Working the other way around my volt drop would be:

V = I*R = I * r * L = 0.3 * 0.227 * 6 = 0.4V

Which I consider perfectly acceptable.

Of course if you were to use a "ring-main" of ribbon cable, then you could clamp on a connector at any point to tap off power to a relay board. The resistance would then be halved (worst case). For example a layout in a room 3m by 4m might use a ring-main 14m long (the circumference of the room). The worst-case run from throttle to track is two 7m lengths in parallel. If you were using some double headed trains in OO scale then the volt-drop would be:

V = I*I * r * L/2 = 0.4*2 * 0.227 * 7/2 = 0.635V

which might be considered acceptable for the double headed trains.

Of course garden railways need much thicker cable. The currents are larger and the cable runs much longer. Suppose a typical length was 20m and we were double-heading and so wanted to supply 1.6A, but accepted a full 1V drop (G scale throttles have more volts to play with than OO throttles) then:

r = V / I / L = 1 / 1.6 / 20 = 0.031 ohms per meter and so you might need a 19/0.25 or 32/0.2 wire.