Is 18 gauge wire sufficient for N scale layout?


Night Train

Night Train

Member
Planning to use 18 gauge solid for my bus and track connectors. Going to have at least 10 track connections going on. Will run no more than 3 locos on layout.

Layout is the Philly-Reading...13 foot x 6 foot layout using Prodigy Express DCC.

Yea or Nay?
 
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18 is a bit light for the bus, but would be OK for the feeders......not sure if that counts as a yea or a nay.
 
I use 18 for feeders and 16 for trunk (bus) lines. There was a discussion of this awhile back with most saying around a minimum of 16 for bus lines.....as best I recall. 18 might work without much margin for overload.

Yeah, Carey said it best.
 
Thanks for the replies. I'm going to use 14 gauge for the bus and 18 for the feeders. Really trying to do this right for the sake of smooth and reliable operation.

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With this being N scale, you could go with smaller feeders for the track, as long as they weren't more than 18" long. The smaller feeders would be a lot easier to hide, unless you're going to solder the feeders to the underside of the track.
 
Here's more than you want to know: A rule of thumb is that the resistance of #10 AWG copper wire is about 1 ohm per 1000 ft. and doubles every 3 wire sizes. A #19 AWG wire would therefore be around 8 ohms per 1000 ft. A 13x6 layout would add up to almost 40 feet of wire and a round trip of 80 ft with around .6 ohms. There would be a voltage drop of about .6 volts at one amp for #19 wire -vs- .025 for #10. A pair of 6 inch 19 AWG feeders would only add an insignificant .008 ohms. With PWM control we're dealing with peak currents much larger than the average and that drop across a #19 wire is even more significant. With the smaller wire sizes each loco would have a significant effect on the others, 18 AWG is probably unacceptable.
 
IshkaBibble said:
Here's more than you want to know: A rule of thumb is that the resistance of #10 AWG copper wire is about 1 ohm per 1000 ft. and doubles every 3 wire sizes. A #19 AWG wire would therefore be around 8 ohms per 1000 ft. A 13x6 layout would add up to almost 40 feet of wire and a round trip of 80 ft with around .6 ohms. There would be a voltage drop of about .6 volts at one amp for #19 wire -vs- .025 for #10. A pair of 6 inch 19 AWG feeders would only add an insignificant .008 ohms. With PWM control we're dealing with peak currents much larger than the average and that drop across a #19 wire is even more significant. With the smaller wire sizes each loco would have a significant effect on the others, 18 AWG is probably unacceptable.
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Did you mean unacceptable for the buss?..........or feeders also?
 
Sure, 18 AWG is fine. By the rule of thumb, 22 AWG would only be .016 ohms for a pair of 6 inch feeders. My choice would be 20 AWG stranded. Don't use mechanical connectors, the become resistive over time. Soldering is the only way to go and be sure that all the strands are soldered.
 
Night Train said:
Planning to use 18 gauge solid for my bus and track connectors. Going to have at least 10 track connections going on. Will run no more than 3 locos on layout.

Layout is the Philly-Reading...13 foot x 6 foot layout using Prodigy Express DCC.

Yea or Nay?
Click to expand...
I don't know what the Philly-Reading is but assuming this is around the room and not a table layout, then the longest bus run would be 19 feet. As the math from the prior posts show that would only be a voltage drop of 0.6 for 40 feet. I don't know what the standard output from a Prodigy Express is but most DCC systems are in the 17.5VDCC to 15.0VDCC range, so whacking 0.3 V off that is not a significant amount. I would be more concerned about locomotives that have a huge current draw, which you also don't seem to have. So had it been me I would have used the 18 gauge for the bus. 19 feet isn't really all that much of a bus.
 
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Maybe we're beating a dead horse here, but keep in mind that an under-the-table bus with #12 solid wire won't cost much more than a #18 stranded and is much easier to strip and solder taps. A drop of .3 volts doesn't sound like much from a 17 volt supply, but you have to consider real operating conditions. A DC driven motor probably won't start rolling with 3 volts and will probably run faster than you'd like with 4 volts and it's tough to make a realistic start. When you're trying to operate at low speeds that .3 volt variation is a very big deal. The why is a little complex, but it has to do with the back emf (electro-motive force), where a spinning motor tends to act like a generator.

At rest there is no back emf generated and the current is the result of the applied voltage divided by the total resistance. Once the motor starts spinning the current is the result of the applied voltage minus the back emf divided by the resistance. With a fictional frictionless motor and no other loads the current would drop to zero because the back emf would be equal to the applied voltage. In the ideal world and with the motor spinning, the speed will be directly proportional to the applied voltage and the current will be directly proportional to the load.

In the real world the resistance of the motor windings, internal wiring and external wiring all gets into the act and the "effective" applied voltage is the source voltage minus the product of the current and the resistance. In this real world, the current will drop once the motor starts and the effective applied pops up, it’s difficult to achieve a smooth start and the more resistance in the circuit the worse the starting lurch will be.

When you’re operating at low speeds and even with a constant load, as you slow down the back emf decreases, current goes up and the “effective” applied voltage decreases. The end result is that you’d slow down disproportionally to the applied voltage and you can’t achieve the slow speeds you’d like.

An extra .3 ohms resistance from the bus wire will affect performance and you may not like it. The penalty of starting with a #18 bus wire and having to re-wire with a heavier wire is severe, let caution rule and start with the heaviest wire you can afford.

Rich
www.railroadmicro.com
 
At least dead horses don't complain when you beat them. I think it was Yogi Berra who once was quoted...."In theory, theory and practice work the same, but not in practice".
 
the Philadelphia & Reading trackplan is in 101 Trackplans, By Linn Wescott, published by Kalmback(plan 97 I believe).
 
otiscnj said:
the Philadelphia & Reading trackplan is in 101 Trackplans, By Linn Wescott, published by Kalmback(plan 97 I believe).
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Ah, I should have thought to look in 101. That is a serious "not around the room" railroad. I see at least six reversing sections. If you place the the DCC command station near the front (left) center, it looks like the longest bus run would be about 10 feet back to Williamsport, and the opposite way in a "t" back toward Reading/Sunbury.

When you were talking about 10 feeders, I assume you mean just for the main, because I see the need for 25 right there in Philadelphia.
 
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