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Wire size for track feeders #18 VS #12

L LIONEL6457OGR Forum Member
BEFORE I saw the most recent discussions on wire gauge size for the feeders coming off a buss line I used some #18 stranded wire for the feeders inside a tunnel. With some difficulty I can get to those wires. I have purchased some #12 wire for the rest of the layout. Should I go back and replace those 6 wires with #12?
Thank you
LIONEL 6457
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FM Former Member
Just make sure you don't fuse your set up with an ampacity greater than the 18 gauge wire can handle.The # 12 wire can obviously handle a great deal more load.

My suggestion is don't go back and try to fight getting #12 wire in the tunnel but mount a fuse block where the 18 gauge wires are and connect them to the smaller fuse. That way if you have a problem with the 18 gauge wire it won't burn like dynamite fuse because it's fused to high.

David
Michael HokkanenMichael HokkanenOGR Forum Member
quote:
Originally posted by LIONEL6457:
BEFORE I saw the most recent discussions on wire gauge size for the feeders coming off a buss line I used some #18 stranded wire for the feeders inside a tunnel. With some difficulty I can get to those wires. I have purchased some #12 wire for the rest of the layout. Should I go back and replace those 6 wires with #12?
Thank you
LIONEL 6457


MY LHS has used #18 and even smaller for year on layouts that sometimes run 8-10 hours a day with no problems.
gunrunnerjohngunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
I think all the flap about fusing correctly for a short feeder from the main bus is pretty silly. From the Handbook of Electronic Tables and Formulas, the maximum current for 18ga wire for chassis wiring is 16 amps, and for power transmission is 2.3 amps. Clearly, the short runs don't have to be fused at the lower value. I'd feel very comfortable fusing a layout with a 12ga bus and 18ga feeders at 10 or even 15 amps. The 18ga wire is NOT going to get hot before the fuse of a fast tripping circuit breaker goes.


Try this simple experiment, wire a length of 18ga wire to a 15 amp fuse and then crank up the power and see which one goes first.

Hint: It won't be the wire!
FM Former Member
quote:
Originally posted by gunrunnerjohn:
I think all the flap about fusing correctly for a short feeder from the main bus is pretty silly. From the Handbook of Electronic Tables and Formulas, the maximum current for 18ga wire for chassis wiring is 16 amps, and for power transmission is 2.3 amps. Clearly, the short runs don't have to be fused at the lower value. I'd feel very comfortable fusing a layout with a 12ga bus and 18ga feeders at 10 or even 15 amps. The 18ga wire is NOT going to get hot before the fuse of a fast tripping circuit breaker goes.


Try this simple experiment, wire a length of 18ga wire to a 15 amp fuse and then crank up the power and see which one goes first.

Hint: It won't be the wire!



You think it's silly but as the old saying goes :There are a thousand ways to do it ....But only one correct way.

There are all kinds of flammables both on and under a train table and you can use the excuse that "We've always done it that way" or "So and so told me to do it that way"

People used to drink out of lead cups too.

David
gunrunnerjohngunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
IMO this does not run the risk of any of those terrible things you're picturing. Note that I agree you should fuse the feed for any type of wiring anyway. I'm not losing sleep over the possibility that #18 feeders are fused at 15 amps, and I don't visualize them as even getting warm before the fuse blows.

I simply don't agree with your contention that my way is not a correct way. Oh, and there is rarely only one correct way to do most things, this task included.
gunrunnerjohngunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
I also point out that the Lionel 180W PowerHouse has a 10A breaker and a nice long run of #18 wire to the Molex connector on it's output. I was testing capacity and I had four 8 ohm 75W resistors paralleled on the output for a 2 ohm load. The PowerHouse supply kicked out 9.5 amps at 17 volts under what is pretty much a full load. The wire doesn't get warm at all after running for an hour, but the Molex connector was a bit warm, not bad but noticeable. Smile

If it's good enough for Lionel, it's good enough for me. Big Grin
AP Arthur P. BloomOGR Forum Member
quote:
watts is what matters not amps.


Wire is rated for the amount of current (amperes) that it can carry. No need to use Watts, and then try to guess the voltage, then do the Ohm's Law math. You just wind up back at current. All the wire ampacity tables, such as the ones in the linked website for boat wiring, are in amps, by definition.

Same goes for fuses and circuit breakers. They are all rated in amps.
E 400eOGR Forum Member
quote:
Originally posted by Arthur P. Bloom:
quote:
watts is what matters not amps.


Wire is rated for the amount of current (amperes) that it can carry. No need to use Watts, and then try to guess the voltage, then do the Ohm's Law math. You just wind up back at current. All the wire ampacity tables, such as the ones in the linked website for boat wiring, are in amps, by definition.

Same goes for fuses and circuit breakers. They are all rated in amps.


I am not guessing at voltage, I know a prewar z is 25 volts, my circuit breaker is 10 amps, my wattage will be 250 max, = 2.5 amps, 18 gauge will work no problem and be at 25% duty cycle. My point is KNOW your max amp draw then use the chart to size the wire then use the voltage drop calculator to size the mains. The way some guys tell you to wire you could plug the layout into a 110 outlet and be safe, there is no need because the ampacity of the wire goes up as the voltage goes down. At the end of the day an 18 gauge drop a foot long, with a 10 amp circuit breaker, at 50 volts or less, will NEVER be a problem in any way.
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