Track Wiring:

There are times when a larger wire may be better. While you could "get by" with #18, a #12 or #14 for the main bus line would be more beneficial. On a large layout where there are many locomotives on at tracks at the same time voltage drops make for a less than desireable operating session.

Anyway, here is a little calculation that should make the point. With a 12 volt 5 amp circut 18 gauge wire loses 1.3Ohms per 100 feet, 16 gauge .818 Ohms per 100 feet and 14 guage wire .516 Ohms per 100 feet.

Remember a 25 foot length of wire has 2 sides or a total of 50 feet of wire. The voltage drop is the same for both sides.

So for 18 gauge wire you lose 5A x 1.3Ohms / 2 = 3.25 Volts in the wire, leaving less than 9 at the loco. 16 gauge: loses about 2 Volts, and 14 guage loses about 1.25.

It shows that 18 is almost certainly a bad idea, 16 might be ok, 14 is a good idea, and if you are going longer you might want even more. To an expert this seems like overkill, but the extra expense and difficulty in going to 14 gauge isn't much to ensure you don't have a problem later on. Technology in this hobby has been growing rapidly and new things we haven't even though of yet may require power through those same wires soon. Don't get caught later without power, plan for it now.

The DCC signal isn't added onto the power 'signal', it IS the power signal. The reason you might lose the DCC signal is because of the power loss. Because of the nature of the DCC signal, the decoder might still be decoding long after the level has dropped to the point that it can't drive anything.

The voltage drop for a 2-wire, 25’ run using 18ga will be 1.646 volts. Now if your power supply is for example, a 12 volts you would only have 10.354v available to the trains. A loss of over 13%! Take into consideration other factors such as rail joiners and connections and it is conceivable that you will loose or “drop” 2 volts.

Using the example with 14ga wire the drop will still be .648 volts. What that means is that even thought the circuit has the ability to provide enough current, your power supply will not have the ability to overcome the loss using small wire. Wire is so inexpensive in the scheme of building a model railroad it is the last place you want to economize. 14 gauge wire isn't that expensive in bulk, especially when you consider it as a percentage of what the entire layout is costing you.

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Wire Gauge Selection Table

Circut Amperes for 6 Volts	Circut Amperes for 12 Volts	Circut Watts for 6 Volts	Circut Watts for 12 Volts	3 Feet use Wire Gauge	5 Feet use Wire Gauge	7 Feet use Wire Gauge	10 Feet use Wire Gauge	15 Feet use Wire Gauge	20 Feet use Wire Gauge	25 Feet use Wire Gauge
0 to 2.5	0 to 5	15	30	18	18	18	18	18	18	18
3.0	6	18	36	18	18	18	18	18	18	16
3.5	7	21	42	18	18	18	18	18	18	16
4.0	8	24	48	18	18	18	18	18	16	16
5.0	10	30	60	18	18	18	18	16	16	16
5.5	11	33	66	18	18	18	18	16	16	14
6.0	12	36	72	18	18	18	18	16	16	14
7.5	15	45	90	18	18	18	18	14	14	12
9.0	18	54	108	18	18	16	16	14	14	12
10	20	60	120	18	18	16	16	14	12	10

Editors Note: Alan Gartner has a great page devoted to the reasoning for this on his website Wiring for DCC.

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