Depends on how large your layout is, how long said wires will be, and how much power your locos draw.
If you layout extend 50 feet around the room, #18 will be too small, there will be too much voltage drop. Even #16 would be too small for that long a run. If yor layout is around 4x8 in size, then #18 will be fine, even with O scale.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Wire gauge recommendations seem to nearly always be extreme overkill because people refer to references for 110 Volt AC usage instead of our lower voltage DC or DCC (DCS) requirements.
But as suggested, you should ask this question over on the Classic Toy Trains Forum because that's where the O scale modelers hang out.
The Classic Toy Trains forum would be a better place to ask this question, as that's where the O-Gauge Gang hangs out.
A lot depends on the size of your layout. If you've got a 4x8 and don't plan to expand it, then 16-gauge will probably be enough. Since you are running O with the higher power demands, I would recommend a track bus with 14 or even 12 gauge wire, and feeders with 18. The thinner wire is sufficient for feeders, as long as they are spaced every few feet, but you should go with heavy wire for your main track bus.
It takes an iron man to play with a toy iron horse.
May or may not be much help, but here is my $.02.
I model in HO scale and I don't know off hand the power requirements of O. I figure 1.5 amp max for sound DCC's, so let’s figure 2 amp for O averaging. 18 gauge wire is pretty small to me as it carries 6-7 amps safely. If you have three 2 amp draw engines running you’re maxed out. 16 gauge gives you 8-10 amps to work with, or 5 engines. Sufficient for most people but figure in on how much you want to run plus accessory draw, lighting, etc.
Keep in mind that the more amps you pull, the more the wire will heat up.
I use 16 or 18 gauge wire just for track feeds, ran into a 14-12 gauge buss line, wired to track every 3-5 feet myself. I usually over wire but I'm also wiring a large club layout that may have 15-25 HO trains running at any given time and I want to make sure it never dies on us. Also larger wire is easier to sloppily solder. (=
DCS recommends 16 gauge wire, but as you add more engines those power requirements will go up. If I were you, I would wire 18 gauge for track feeds if you already have it and use 14 gauge for a main buss line (17 amps). This would give you plenty of room to expand and you could comfortably run anything.
If you only want to run 1-3 engines, 18 is acceptable depending on how large the layout is and if you have a buss line. If you have only a few power feeds, spend the extra $$$ and use larger wire.
Re-wiring isn't fun so plan ahead for future needs. (=
Well that's my $.02.
I'm just starting out with MTH DCS System for my o scale layout. I have 18 guage wire. Can I use that to wire my layout? Some of the guys I have talked to said to use 16 guage wire, and othe guys told me 18 guage would be fine. I just want to get different opinions on this subject. Thanks.