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Wiring part 1 : the basic rules

On this layout, I use a system of "Bus" to distribute power supplies such as DCC, lighting models, turnout motors, electronic circuits, etc.. . .
Here, the "Bus"is a twisted pair of single strands wires 1.5 mm , which runs along the entire layout.

From this bus, I feed all the points with wires of smaller gauge (AWG 22 and 26).
You will find at the bottom of the page, a matching table between AWG (American Wire Gauge) and mm .
You will also find the various laws that allow the calculation of the cable sections.

This page is partly inspired by the work of Allan Gartner with his kind permission.
Visit his website about wiring and DCC, garden train and much more : Wiring for DCC (see links page).



Rule n 1 :
Specify a color code and stick to it.


Here is my color code :

Blue - Gray : DCC main bus
Blue - Black : DCC secondary bus (Block bus)
Blue - White : DCC rail feeder
White - White : 12 V AC stuctures lighting
Orange - Grey : 12 V AC turnout motors
Red - White : 18V AC DCC station power supply
Black - Red - Blue : 12V and 24V DC for all electronic circuits and relays.
Green : frog of the turnouts

On this picture, you can see various buses that running through the layout.

Note the smaller section wires (AWG22) supplying a piece of rail from the DCC bus.




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Rule n2 :
Never use undersized wires, there are risk of overheating and even fire !


On this layout :

1,5 mm twisted pairs : the Bus
AWG22 : Rail feeders
AWG26 : Connections between bus and turnout motors, lighting models, etc..

The AWG 22 and 26 wires are stranded for greater flexibility.

4 pairs telephone cable 0.6 mm :
to command the signals, switches, etc..


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Rule n3 :
Make good solders.


Use a soldering iron suitable for work, 40 to 60 W
seems to me to be a good choice.

Choose it with interchangeable tips, use a fine tip for electronic circuits and a medium tip for wiring.
(see photo)
Prefer tips "long life" made of alloys Cu - Fe - Ni - Cr
rather than tips made of copper that oxidizes rapidly.
This tip should be well tinned and clean.
Choose the solder electronic type made of 60% Sn and 40% Pb with a diameter of + / - 1.5 mm.
Plan a damp sponge to wipe the iron before and after each solder.
Never breathe on a solder to accelerate its cooling, it will weaken it
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Rule n 4 :
Each piece of rail must be solded to something :

- either to the DCC bus or to the next rail
- via 2 wires stranded AWG22 or equivalent.

Do not trust the rail joiners for electrical conductivity, their role is limited to a mechanical holding and to the alignment between the rails.

Step 1 : Preparation of the rails for soldering.

Before soldering, the rails must be free of varnish, oil or other polluting residues from their manufacture.

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Step 2 :  tinning of the wires and the rails.

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Step 3 : soldering of a AWG22 wire on each rail, respecting  the color code and the "polarity".

Although the DCC is an AC square signal , you must follow the "polarity" between rails otherwise you'll get a short-circuit!

  N.B.
To the eye, a good soldering should be bright.


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Step 4 : Preparation of the bus before installation on the layout, it will facilitate wiring when you will lie beneath the structure.

Here, I prepare each connection point, two AWG22 wires that will be connected to both rails wires.

This bus is twisted with a simple drill,
from 1.5 mm solid wires, the type used in electrical housing installations.

Why do I twist the wires:
1 - Increases its mechanical rigidity.
2 - Enables better identification Bus.
3 - Reduces cross talk between the wires, ie, the electromagnetic influence of a bus to another.


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Step 5 : soldering of the AWG 22 wires from the rails to the bus of the concerned block.

During this operation, cut the wires as short as possible.
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Step 6 :
Isolation of the connections.

For this operation, prefer the shrink sleeve to that sticky stuff that always end up to come off!

The layout wiring should last for years !

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Next step : comfort is also important when you must wire for hours!

Note the small pillow under the head!

You will find a description of this little truck on the Special Tools page.
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Rule n 5 : 
Choose connectors to be solded or crimped.


When you need to disconnect some cables in the layout (eg, the junctions between modules), prefer the connectors to be soldered or crimped.

Here are different types of terminals "Fast-On " well known in automotive wiring.
They offer a good contact, are available in various sizes, highly resistant to manipulations,  easy to find and cheap.

However, for a proper use you should:
1 - Use a suitable crimping tool.
2 - Adjust the size of the terminal to the size of the wire.
Warning: this terminal is designed for stranded wires.

There are specific insulators (see photo).
However, a shrink sleeve will be just fine.
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It is possible to use these connectors "Fast-On " on  solid wires if we take some care:

Step 1: crimping

In this case, the crimping does absolutely not give a good electric contact.
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Step 2: Solder the terminal on the wire.

This will severely restrict the contact resistance and will ensure a good mechanical strength.
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Rule n6 :
the stranded wires fixed by screw must be tinned

This will assure them a good surface of contact and greatly enhance their mechanical strength.

If you need to connect multiple wires in the same terminal strip 1 cm, twist and solder them together before introducing them into the terminal.


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For connection to printed circuits, you can use:
- The solder lug,
- The terminal "Fast-On" on a soldered terminal.
(see photo)

Here is a current detector (block occupancy) , you will find his complete descrition on the
Technical / Wiring part 3  page.

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The basic laws of electricity

Ohm's law : U = R x I
U : the voltage in Volts   R : the resistor in Ohms   I : the current in Ampres

A conducting wire carrying an electric current (I) offer some resistance (R) to the current flow.
This resistance (R) will be greater as the wire is thin and long.

We can calculate the resistor of a conductor (wire) : R = rho x L / s
R : resistor in Ohms   rho = 17 x10 -9 for cupper  L : lenght of the wire in m   s : section  of the wire in mm
The bigger is the Wire section , the lower is the resistance to current flow.

The electric power : P = U x I that could be transformed as : P = R x I
P : electric power in Watts.

Joule's law : W = R x I x t
W : energy (heat) in joules  t : working time  in seconds.
The bigger the wire section will be, the less it will get hot.

Introducing the contact resistance
When you connect two wires together, or a Wire into a terminal, or two rails via a rail joiner, etc.. . .
It appears at the connection point of these two conductors, a contact resistance due mainly
to the oxidation and at the weak contact surface of the metals.

To reduce this resistance, we must :
Solder the conductors to each other and use good quality connectors

Conversion table AWG vs mm

AWG (American Wire Gauge) is a way to express the wire sections.
You'll often find this type of expression in the wires and cables for electronics.

AWG
D mm
S mm
R Ohms / m




13
1.83
2.63
0.0065
14
1.63
2.08
0.0082
15
1.45
1.65
0.01
16
1.29
1.31
0.013
18
1.02
0.82
0.021
20
0.81
0.52
0.033
22
0.64
0.32
0.053
24
0.51
0.20
0.084
26
0.40
0.13
0.134
28
0.32
0.08
0.213

For example : if  I = 1 Amp  and wire length = 10 meters, we will have a voltage drop across this Wire: U = R x I
AWG 26 = 1.34 V
AWG 22 = 0.53 V
AWG 15 = 0.1 V
AWG 15 is equivalent to 1.5 mm wire that the Bus is made of
Meaning that the voltage drop across this bus is 13 times less than in a AWG26 Wire.
Thus, we see the interest of using wires with largest possible section.

Resistivity of the materials (rho) Ohms . m

Metal
Symbol
rho



Silver
Ag
16 x 10-9
Copper
Cu
17 x 10-9
Gold
Au
22 x 10-9
Aluminium
Al
27 x 10-9
Bronze

50 x 10-9
Zinc
Zn
60 x 10-9
Brass

70 x 10-9
Tin
Sn
142 x 10-9
Lead
Pb
207 x 10-9
Nickel Silver

300 x 10-9
Stainless Steel

550 x 10-9

This means that our rails in Nickel Silver (Cu - Ni - Zn) offer a resistance 18 times greater than the copper.
It is thus interesting to connect these rails as often as possible to the power supply (bus).
You also see the very poor conductivity of the association Nickel Silver (rails) with Stainless Steel (rail joiners).

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