18ga wire questions

According to the chart Dale referenced, 18 gauge wire is good for up to 16 amps if the wire is in "free air". I assume that means it is not enclosed in a conduit. Or is there more to it than that?

Dale and C.W. , thanks for the quick replies.

Bob

Thanks for clarifying that Dale. I'm getting ready to redo some wiring and will make sure everything is correct.

Bob

If you have hundreds of feet of #18, and want to use it (and not waste it) you can use two parallel runs to loads that require heavier wire. The formula is very simple for copper wire: if you double the wire conductors, you get a virtual conductor that is three sizes bigger. (Three gauge numbers smaller).

So, two #18 wires in parallel gives you the same ampacity as a single #15 conductor.   (18 minus 3 = 15)

In real life, we electricians are prohibited from doing this when working on line voltage (120/240, etc) except for certain cases in which feeders require really big ampacities in the same conduit,  but we low-voltage train guys can do it safely and without any worries.

Here are a couple other examples: If you have any Cat5 (4 pairs of #24) lying around, and you use all 8 conductors in parallel, that would be the equivalent of one #15.  Cat6 uses 4 pairs of #23, so all 8 conductors of that would yield an equivalent gauge of #14.

Using the CAT5 or CAG6, you'd also have something equivalent to Litz wire for DCS compatibility.

I agree with Dale that 18-gauge wire will cause too much voltage drop, which drop increases as load increases, further aggravating operations.  Arthur is also correct about doubling the number of conductors, which is ok on a train layout but NEVER on higher voltage service or critical or high-amperage service.

I appreciate all the support. The buss wire is 12ga supporting a loop about 150 feet. Some of the feeders are 18ga wire but no more than 18-24 inches. I plan to add another loop. These are not star wired. Can I use the same common buss, 12ga, for both and just run another hot?

Bob

Dale,  Each loop is 150 feet total length. I have a z4000 running both loops. Most of the time I run conventional or TMCC. I have a TPC 400 but never hooked it up. I have more 12ga wire so running another buss is no problem. I plan to hook up smaller loops for future DCS. I do run passenger cars and  the amp meter on the z goes to 8 or 9 sometimes. I will converting to led in the future.  My Lionel CP passenger set has pullmor motors and will quickly go over 9amps on the meter. I'll heed your advice and run more 12 ga wires next week. Maybe I will star wire the second loop.

Thanks,

Bob

Bob, is the loop connected together at the ends?  That will reduce the resistance by being able to feed current in both directions around the loop, cutting the maximum resistance to half what you would have if you have a "T" with a feed at the center and the ends dangling. 

TMCC won't care that it is a loop.

18 gauge is 6.5 milliohms (.0065 ohms) per foot per wire.  If you use 2' feeder on both leads, you will add .027 ohms to the circuit.  With 10 amps of current, that will drop .27 volts just in the feeders.

Hi Dale,  I just checked and it is a complete loop with a wire tapped in to the transformer.  I can shorten the 18 ga feeders to 6-8 inches if you think that will help. This started as temp wiring and due to back injuries it has been hooked up for a few years. I'm feeling better now and need to crawl around and make a solid permanent fix. I am going to get more 12 ga wire this weekend. Thanks for the info. Hope to see you at Cal-Stewart this year. I first met you when you were running your upside down layout, very cool.

Bob

An 8" feeder will cut the drop I calculated above to 1/3 of that value.  That would be much better.

I will be at Cal Stewart.

I want to thank everyone for their help!

Bob