I sure this has been discussed before but I am having some problems with a self-proclaimed expert on a mailing list who asserts that 6 wire flat telephone cable should never be used and Cat 5/5e UTP is the only suitable wire for a DCC command bus. Arguments used include: - "Cat 5e cable can handle higher frequencies, hence is suitable for longer distances compared to flat telephone type cable" - "flat telephone cable is proving to have a problem with interference with runs longer than 10 ft" - "no manufacturer says do not use cat 5e cable for DCC" - "Most manufacturers do not encourage using cat 5e cable simply because they sell hardware accessories that match the [RJ12] telephone plugs" Can anybody help with authoritative advice, especially from DCC manufacturers? Cheers David
There's any number of layouts running Cat 5 rated cables for the interconnects. The flat cable on the other hand isn't overly fussed by interference provided there is separation between the command bus and the track bus as a precaution. Most layout wouldn't have such a great distance between the UTP's to be a problem. NCE sells a 40' flat cable so it must be fine. Digitrax's page on cable making says a maximum of 600' between two devices using flat cable (6-core) but doesn't indicate proximity of other wiring having an effect.
I use Cat5e because I have tons of scrap cable and jacks/ends when I'm working. It's entirely up to you what you want to use. Its just more cost effective to keep the "garbage" in my bag instead of throwing it in the trash. You aren't going anywhere NEAR the max distance (~325ft) or speed of Cat5/5e even really need it. If I went into the nuts and bolts of how the cable operates, everyone who read this thread would fall asleep within 5 seconds. But if you do go to max distance on a Cat5e run, I want to visit and check out this empire. Cat 2/3/4 cable is just fine and dandy. Keep it a couple of inches from your power bus just for sanity's sake (and to keep things neat and pretty). Thats all you need. If a DCC manufacturer says 6 conductor flat cable is acceptable, I'd say there is a reason they said it. If you staple the cable, be gentle and don't pulverize it. If you go Cat5e, Just keep with the cable conventions throughout the whole thing and you'll have no problems. I use the regular 568A standard & RJ45 jacks and ends, and eliminate wires 1 & 8 (white/green and brown) if have to put on an RJ12 end. That way, I have my 6 conductors consistant. I use that standard every day, so its just comes natural now. In a nutshell: use whatever you're comfortable with and have access to, so long as you keep the bus consistant. I tend to stay away from mailing lists because there is typically someone who read something somewhere at some point who read a big word, and is now an expert. (I'm jaded).
From Page 4 of the North Raleigh Club's DCC pages (http://www.trainweb.org/nrmrc/dcc/loconetandloconetcables.pdf): "While communications cables with more than six conductors (such as 8-conductor Ethernet cable, 25-conductor serial cable, etc.) can be adapted for use with LocoNet, their electrical characteristics are not suitable. The voltages do not match, the pinout does not match, the cabling is different, the RJ plug is different, the protocols are different and the cable capacitance is different, generally too high. Use of such cables will draw down the LocoNet voltage too much, and when the LocoNet voltage drops too low performance can become flaky. The bottom line — use only 6-conductor telephone cable for LocoNet." While most of the above issues above can be dealt with in planning and implementation, the capacitance of the cable cannot. The Cat 5 standards assume a certain capacitance per ft. and cable terminations are designed based on this. LocoNet was designed assuming 6 wire flat cable, which has different characteristics. Cat 5 may work (and be cheap), but it is not optimum. YMMV.
Just finished setting up our NTRAK layouit in the B & O museum. Over 400 feet of flat satin cable on the layout. No problems now or the last 6 years. At DCE, they went through two and a half 1000 foot spools. That's in addition to the cables that were brought in already made up. Doug, you probably know best how many feet of loconet cable was run at Chantilly. We had 200+ feet on our loop, but that wasn't connected to the red line DCC. A.J. Ireland (owner of Digitrax) told us that flat 6 wire cable is the best to use. He does not recommend Cat5e. I'll stick with what the designer of the equipment says to do. Martin
Something nobody has mentioned is the fact hat different manufacturers use different signaling methods. Digitrax's Loconet uses a single-ended signaling method and will not benefit from twisted pair cabling like cat5 but actually perform better in the cabling it is designed for. Lenz and NCE both use RS-485, a differential signaling method that will work better over cat5; however, at the speeds and distances we deal with it really doesn't make any difference.
Well this is just another area where wiring is misunderstood. Assuming Cat5/e would be better was not based on understanding the signaling technology used, or the frequency of the signal being used. I guess is was just, since my computer uses Cat5 to communicate, it must be good also for DCC. They both are Digital signals. The selection of digital cables is based on the type of signal being used. The Ethernet protocol is vastly different than the DCC protocol. First the DCC protocol is so much lower in frequency, the cable reactance would be totally different than the cable reactance at 10/100/1000 woo woo woo/s. DCC is an always on protocol, where the ethernet is not always on. Because of this, there would be a lot more power loss in the Cat5 than in the flat phone cable. When evaluating any wire you need to look at the type of signal, the quality of the wire. It just isn't good enough to make blanket statements based on observations in other technologies. Modulation causes more frequency content to be transmitted and received. And you have to look at the frequency range of operation for the correct answers. It also makes a difference if the cables terminate in balanced or unbalanced load. Using LocoNet, this is not much of an issue since the cables are terminated in the devices with a matching load. The same holds true for buss wire. Using the AWG to size buss wire is also incorrect. In each case the numbers were derived emprically using DC and 60Hz AC only, and using the least quality grade wire. No analysis of the conductance or the reactance at DCC frequencies was ever looked at. And the quality of the wire, not the size of the wire, makes a bigger difference. But again, decisions were made looking at the wrong model using the wrong frequency domain.
I have used cat 5 form my digitrax loconet and "seem" to have no problems (except self induced LOL). This topic is interesting and has me considering changing the wire. In my local area I have been unable to locate flat telephone wire. Correct me if I am wrong but I understand the flat wire is stranded. I can get 6 wire round telephone cable I understand this cable is made from solid. My question is there any reason to use one over the other or is it that comparing the two - wire is wire? Tom
