Raised on the Erie Lackawanna Mainline- Supt. of the Black River Transfer & Terminal R.R.
First, don't be concerned about a fire hazard. 14-gauge wire is rated to 15 amps, I believe, and the meatiest DCC boosters are only 8.
I would leave the present wire in place. For the new section of the layout, run a new bus all the way from the base station with 12-gauge, assuming it's going the longer distance. It's fine to branch your track bus. Just don't loop it back on itself.
I'd also consider re-locating the base station to a more central location, so that 50-foot run might end up being two 25-foot runs instead. Depending on the number of tracks and locos, this would be a good time to consider true "Power Districts," electrically isolated sections of the layout, each with its own booster. Wired properly, you'll never notice when your train crosses from one to the other, but the load is spread among the booster units rather than all coming from the same source. If you're not up to boosters just yet, then isolate the tracks anyway as you install them, and install a few circuit-breaker units. This will help with troubleshooting when electrical problems arise. (Not if, when. Sorry. It's gonna happen.)
18x65 feet? Lucky Girl indeed. Hmmm, not a bad screen name, either.
It takes an iron man to play with a toy iron horse.
There's no need to rewire anything. For DCC, she should add a power booster in the add-on room. To do this, a separate power supply in that room could power the layout there and the only interconnection between the current command station and the booster would be a telephone wire or whatever is required to carry the command signal from the base station to the booster.
If she uses a power strip or surge suppressor to turn the layout on and off, an extension cord could be ran from there to the new booster's power supply so it too is turned on and off with a single switch.
Remember to add up the amps of the boosters and base station, so you don't overload a single household circuit. If you've got a 15-amp breaker feeding the wall socket, then you don't want to put two 8-amp boosters on it. In reality, they'll never end up drawing that much, since you probably don't have enough trains to get close to that capacity, but I'd still try to distribute the boosters to different circuits (not just different outlets on the same circuit) to be on the safe side.
EDIT: This isn't right, as Martin points out below. The 8-amp booster isn't putting out 8 amps at house voltage, but rather at track voltage. So, you have to convert to wattage, then back to amps at house voltage, and you'll find an 8-amp booster draws about as much power as a hundred-watt light bulb. I'd put them all on the same outlet strip for convenience.
Never mind.
I agree with both posts above. Keep the 14 guage wire and use 12 guage for the new room. The only thing I dissagree with is looping the power bus. There is no reason not to loop the power bus if you want to. It is no different than the track being looped. The advantage is that you have a power bus coming from both directions which will help keep the voltage at its highest level at the furthest point.
Bill
Bill54There is no reason not to loop the power bus if you want to. It is no different than the track being looped.
In theory, you should loop neither the bus nor the track. You should provide an insulated gap at the furthest point along, and wire the loop as if it were two separate branches.
The DCC signal is a modulated square wave. As the wave front goes out on two different paths, everything is fine. Where two paths come back together, though, the waves should ideally be kept "in phase" with each other. If not, when they meet, they will interfere with each other and "muddy up" the signal a bit.
In practice? Who cares? Relative to the speed of the signal in the track and bus wires, the modulation on the DCC waveform is very slow, so the amount of destructive interference is minimal, and would be hard to notice without putting a scope on it.
With Aluminum 14 Gauge wire 65 Feet, and 12V DC source, she'll drop 1.7 Volts @ 3 amps.
http://www.csgnetwork.com/voltagedropcalc.html
The problem isn't the voltage or length. After all you can run telephone wire for thousands of feet without a booster/heavier gauge. The problem is the current. The more current you push, the larger your drop in voltage.
But if her room is that large, she might consider breaking her layout into blocks and running seperate supplies to each block. If she switched to DCC then she could use blocks with boosters.
I better shud-up now. With all the posting I'm doing today, someone might actually think I know what I'm doing.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
DigitalGriffinWith Aluminum 14 Gauge wire 65 Feet, and 12V DC source, she'll drop 1.7 Volts @ 3 amps.
Well that's true, but who uses aluminum wire for a bus? Generally its only used for heavy loads (30 amps & up) when the cost of copper is prohibitive. Did someone find an old cache of pre-prohibition romex cable? Don't nick aluminum wire when stripping it or it will break.
The voltage drop is only 1.2 for copper BTW. Should be fine.
Also this is 65 feet from source to load just in case anyone gets confused.
The mind is like a parachute. It works better when it's open. www.stremy.net
MisterBeasleyRemember to add up the amps of the boosters and base station, so you don't overload a single household circuit. If you've got a 15-amp breaker feeding the wall socket, then you don't want to put two 8-amp boosters on it. In reality, they'll never end up drawing that much, since you probably don't have enough trains to get close to that capacity, but I'd still try to distribute the boosters to different circuits (not just different outlets on the same circuit) to be on the safe side.
The power supply for an 8 amp booster supplying 16 volts will pull just over 1 amp on a 120VAC circuit. You could safely run 8 - 10 boosters on a 15 amp circuit. That would be if all 10 were supplying the full 8 amps, which they won't be.
As far as wire size, more than a 1 volt drop is too much and will come back to haunt. 1.2 volts on HO is 7.5%. Try to keep the voltage drop under 5% for reliable operation .
Martin Myers
mfm37 The power supply for an 8 amp booster supplying 16 volts will pull just over 1 amp on a 120VAC circuit. You could safely run 8 - 10 boosters on a 15 amp circuit. That would be if all 10 were supplying the full 8 amps, which they won't be.
Y'know, he's absolutely right. I'd completely forgotten that your trains aren't running at full house voltage, so the current draw from the outlet isn't 8 amps, it's more like 1.
Go ahead and plug the boosters into the same power strip. No problem.
Capt. G:
How many locos are we talking about here per block?
Here, have a chart:
http://www.powerstream.com/Wire_Size.htm
One thing to remember is that if a wire burns out carrying 100A, it doesn't matter whether it's 100A 120V or 100A 6V...current carrying capacity doesn't involve voltage. Your car uses large wires because the currents are similar to your house current, even though the voltage is too low to shock.
However, it's going to be hard to burn out a large model RR bus wire. For one thing, we are running individual wires in air, not cable or conduit runs, which gives better heat dissipation. House wire is very conservatively derated because it isn't in free air. The table above shows that 14 AWG copper unbundled, exposed chassis wiring in free air is allowed 30A, and that's still conservative. You can run a lot of locos on 30A.
You don't want 30A on the bus, however, because if there's a short, that full 30A will flow through it, and may do nasty things to the shorting equipment. It may also burn out the feeder wires - if you're using stout 18AWG feeders, they've only got half the current capacity; these probably won't go, but small feeders might. The thing to do is divide up the RR into sections with reasonable potential current demand, perhaps 5A, and use the big bus so there isn't major voltage drop.
Voltage drop may or may not be a problem. 14AWG has about 2.52 ohms resistance per 1000'. A 50' long piece will have about .13 ohms. Calculate voltage drop by multiplying resistance and current (Ohm's Law, E=IR). At 1A, you're dropping .13v, and at 10A, 1.3v. I don't know if I'd want to go any higher than that on any given bus section, but I've never had a model RR that drew anywhere near that much - some people have, especially some Lionel operators.
Edit: I wouldn't expect wires to burn out the minute you cross the capacity line, of course. They might get hot, then they'll melt the insulation, and with increasing current you'll make a nice little toaster out of them. I have burned out wires instantly with 12v, however. In one case, I was using a wire of ~18 gauge to do some tests on a car, and accidentally created a short. It cleared itself quickly. Poof! According to my calculations, given the wire size and length, the wire passed about 200A in the instant before popping.