I've used undersized wire for the drop feeds from my power routed n scale turnout frogs. I'm not sure what size it is but it is definitely smaller than the recommended gauge for drop feeds. I can splice in thicker wire under the layout boards but that would leave 2 inches (depth of the foam board) of under sized wire - am I likely to have problems? Thanks
It's very unlikely to cause problems if you keep them short. The volt drop on a wire depends on the resistance per unit length times the length, so a short piece of small wire won't add much to the losses. However, you should avoid feeding long sections with small wires - not a problem if you are putting in drops every few feet. If these are just feeding the frogs, then there'll only ever be one loco there, so definitely no problem. My wiring is metric, but I use fine fuse wire (about 5 Amp I think) which is about 27-28 awg for the first few inches from the rail through the board, then something insulated which is about 22 awg from there to the main bus which is usually about 6 to 12 inches. Main bus lines are about 14-16 awg. Darn it. Having converted it all to awg I see you're in the UK The 'fuse wire' is 0.35 mm dia (~ 0.1 mm²), my intermediates are 0.6 mm dia (~ 0.3 mm²), and the bus lines are 1.5 mm² cable. But my layout isn't large - if it was I'd probably go up to 2.5 mm² cable for the main bus, but the drops would stay the same.
Feeder drops can use smaller wire, and the smaller it is, the easier it is to hide. That said, you want your bus wires (the ones carrying current to the feeders) to be a good, heavy wires, like 16-12 AWG. For short runs, 18-20AWG is good, but for longer than 10 feet or so, go with bigger stuff. My mainline is about 45', and I used 16AWG for my bus lines, and 20-22AWG feeders, and have no issues.
I will simply re-inforce what has already been said. The drop feed wires on my layout are about 24aug yet the main bus is 16aug. I keep the feeder to no longer than 12" and there are many. The frog wires are actually only about 6" as the turnout control is under or beside the throw rod.
"Am I likely to have problems? I'l put it simply...No! If you are tuning in late I would recommend you read the previous posts to learn...Why?. Have fun!
The thin wires are really problematic, from the point of view of safety, for not being able to pass high amperage through them. Their thinner cross section makes the draw from a short highly resistant, and that in turn causes the wire to warm, even to the point of getting red or white hot for a period. It should be no surprise that this is highly undesirable anywhere except perhaps in automobile cigarette lighters. During a short, say when a metal wheel derails at points or at a fed frog, you get the full amperage wanting to go through that interface. However, obliged to feed that amperage to the affected area is the single set of wires you have chosen. If you have a 5 amp system and 24 gauge wires about 1 meter long in use as feeders, you can expect those wires to get darned good and hot...and smelly. So, as the others have said in slightly different words (fully credit :tb-biggrin, those thin wires are okay except in severe cases of greater necessary lengths and/or higher amperages, generally over the 4 amp and up range. Good rules to think of..if they're gonna be thin, keep 'em short, and keep the power demands which they could be called upon to provide down to 2-4 amps if possible. That means use more of them in smaller sections of gapped track, or what are known as blocks on DC layouts, and power districts on a DCC layout.
If those thin wires are only at the frogs, I think this will be no problem. Any engine will only get power for a short time through the frog. Most engines can bridge the frog. Did you run DCC? Try to shortcut with a coin. Will the booster shut down at once?? Then you're ok. Wolfgang
Given the (quite correct) concerns about shorts further up, 1.7 would not do, but I've checked my facts and the size I use (29 swg; ~27 awg) is 10 amp fuse wire. However, for fuse wire, the current rating is that which it will pass continuously, not the 'blow' rating, which is given by a graph of prospective short current against time. Rewirable fuses using this type of wire are notoriously inaccurate as protection (hence the rise of the MCB and electronic protection) and it is quite possible for them to pass double the rated carrying current for a good many seconds before heating up to melting point. Given that DCC systems have a fast (milli-seconds) and accurate cutout system a short length of thin wire should not present any problems at all. If you run a metre length of the stuff, in direct contravention of the OPs example and the advice given above about that, you will quite possibly have some problems with excessive volt drop. But I suspect that if it was bad enough to overheat the wire it would also be having a dire effect on running trains.
Mike, Lets face it, how much current does a turnout switch draw anyway? 0.5 amps? 10 amp fuse calcs are designed for a fuse length, not over distance, hence the different ratings. Like I said still adequate. Id say its somewhere in the middle. The AWG chart is conservative but correct. Better to err on the side of caution. Rick
The question is to do with track power - a turnout frog is involved, though the original post does not make it clear exactly how. The current could be several loco's worth. ... which is why it has been said above that this is only good for a short length. Volt drop over longer lengths would become unacceptable for proper operations and possible hinder correct operation of the short circuit protection (see ref to the coin test). Anything less than about 5 amps is not adequate as it could expire before the protection trips. It might be OK for a small 2A DCC system, but most are 5A. I don't know which awg chart you are referring to, but if it is to do with use of cables in household wiring it is of limited value here. For applications in the 12-20V range the voltdrop in the wires often limits the smallest conductor that can be used long before the maximum current carrying capacity is reached. Which is why we use heavy-gauge bus wiring for the long runs and short, light-gauge wire droppers to connect to the rails. This picture shows how I do it: I use copper clad panel pins as terminal posts for supporting the bus wires and for connections between my intermediate wires and the 'fuse wire' connections to the track. I have a 5A DCC booster - the 1.5mm² bus cables in the foreground have a 'mains' rating of about 15A, but there is no way I'd consider using 0.5mm² for their job, and in an earlier post I actually proposed 2.5mm² for a larger layout.
Actually, the turnout, like any piece of track, draws nothing. If a loco derails at the turnout (not uncommon) and shorts across the rails, the current can be significant (10 Amps or more if not protected). That's why command stations and power managers have cutouts in the 1.5 to 4.5 amp range that trip in the order of 10s of milliseconds to a half second or so. If you are talking a turnout motor, a pulse of 500 ma for a twin coil solenoid sounds about right, but it's only for a short duration (that's why capacitor discharge circuits are often used). Stall motors draw 5-10 ma when in transition and 15-20 ma when stalled. so the answer is .... "It all depends!" <G>
