Phone jacks fo wiring

Discussion in 'FAQs' started by jaijef, Nov 7, 2006.

  1. jaijef

    jaijef New Member

    Hello all,
    My name is Jai and I back after awhile being off The Gauge.
    I was starting to wire my HO scale layout.
    It is approx. 9x9 and was wondering if I can use an
    In Line 1/8in. Phone jack to connect my terminal wires to the main bus wires so I can connect & disconnect them when I need?
    Is 1/8 to small or what is the recommended practice for this?
    I am running a No. 14 AWG bus w/no. 18 AWG feeders.
    A friend told me the in line phone jacks will not work for DCC but I am doing DC until I can convert to DCC.
  2. MasonJar

    MasonJar It's not rocket surgery

    There are a few things within your post, and I will try to answer them as best I can.

    I would not use telephone wire to carry power to the layout, especially since you have gone to the trouble of creating a 14 ga bus. At the modular club I belong to, we use the "flat 4" trailer plugs to connect modules together (this is for powering two mains - for one main, we either pair the wires, or use the "flat 2" type - see more on standards at

    The other problem with telephone wire is that it is solid, so any little nick in the wire can cause a weak point where it is likely to break in the future - probably in a hard to find spot at a really inconvenient time... ;)

    There are all kinds of connectors available at electrical stores, or even the local Home Depot. If you don't have to meet any specific standard, then you could choose one of those instead.

    Phone jacks will indeed work for DCC but not for power - for communication. In fact that's what (for example) the throttles and other "LocoNet" components plug into. BUT - they are the six wire RJ-12 type, not the standard household four-wire.

    Hope that helps.

  3. shaygetz

    shaygetz Active Member

    It also can be very, very light stranded copper around a nylon cord, again very thin and a bear to splice.
  4. LongIslandTom

    LongIslandTom Member

    I was a bit puzzled when jaljef said "1/8-in phone jacks.." I've heard of RJ12, RJ45, etc. phone jacks.. But never 1/8" phone jacks.

    Maybe he meant 1/8" headphone jacks for stereo equipment...?

    The modular club here on Long Island I used to run with also used flat-4 trailer plugs.. I've never used headphone jacks for this application so I don't know if it will work or not..
  5. MasonJar

    MasonJar It's not rocket surgery

    Oops! I think you are right Tom... :oops:

    The TELEphone jacks are used in LocoNet wiring, but the phone (phono?) plugs can be used for power. A member of has powered a turntable - and provided a pivot point - using a 1/4" phono plug.

    The main challenge is to match the plug/socket to the wire gauge so there is no added resistance. There is no point in having a 14 ga bus if the 1/8" phono connection piles on the resistance to the transfer of power...

    Sorry for the misinformation. I'll have to read more closely...! hamr

  6. Jim Krause

    Jim Krause Active Member

    I'll go along with the four wire trailer connectors. We used them on the club layout when it was a modular system and they worked very well.
  7. doctorwayne

    doctorwayne Active Member

    Jai, do you actually need to physically disconnect the wires, or are you talking about disconnecting the power? For the latter, a simple toggle switch will work fine.
    A question for everyone else: my power pack, an MRC Controlmaster 20, is controlled by a hand-held throttle, tethered on the end of a 36' springy-type 'phone cable. While there is a heavy-duty bus wire, it merely connects the multiple jacks placed on the layout facia around the room, and thence back to the power unit. I believe that the hook-up wire from there to the track, about 4' long, is #16 wire. By all accounts, I should be experiencing voltage drops like crazy, yet I can run heavy trains with 5 or 6 locos, and still have power to spare. What gives?

  8. jaijef

    jaijef New Member

    thank you

    thank you for the information it was helpful.
  9. Russ Bellinis

    Russ Bellinis Active Member

    Was the throttle tether engineered by MRC to work with the control master? They may have used a wire with thinner insulation in order to allow a bigger gauge of wire in the same tether.
  10. doctorwayne

    doctorwayne Active Member

    Russ, the tether that comes with the ControlMaster 20 was a similar type of cord, but only 6' long. It plugs into a standard 'phone-type wall jack. The cord that I'm using was bought at Canadian Tire, and is meant for a telephone. I'm thinking that the reason that I don't get a big voltage drop is because of the way the throttle is set up to work. If the walk-around throttle is unplugged while the train is running, the train will continue to run, gradually slowing, and eventually stopping. If you then replug-in the throttle, without altering your previous speed setting, the train will resume its former speed. I don't think that the actual power that goes to the track also goes through the throttle; perhaps it's just some sort of control signal.
    When I built my house, I did all of the wiring, and had no problems.:thumb: However, anything beyond just getting the trains to run is mostly a mystery to me.:rolleyes:

  11. MasonJar

    MasonJar It's not rocket surgery


    I suspect this is the case.

    The problem is if you put something small enough in line with the power, you run the risk of reduced "transmission" and potentially other problems. After all, what is a fuse except a really small piece of wire in the middle of a bigger piece?

  12. DixonRobertson

    DixonRobertson New Member

    24 AWG telephone wire for turnout control?

    Has anyone tried telephone cable (including punch blocks and RJ-11/12 connectors) for turnout control wiring? I am about to bring on line a CDU for snapping coil switch motors. Will the 24 AWG wire handle the load?

  13. pgandw

    pgandw Active Member

    Because the load is momentary, the wire will not likely create a fire hazard. But it is marginal for the load, especially for longer wire runs, which means a portion of the energy is going to go into heating the wire, and you are not going to see the full voltage at the switch machine.

    Most twin coil switch machines draw on the order of 2-3 amps. Atlas switch machines tend to draw less than others.

    The following maximum safe current loads are based on National Electric Code. They are spec'd based on fire hazard, and ensuring circuit breakers work correctly. If voltage drop is an issue in an application, then a larger wire size should be used. Voltage drop is unfortunately an issue in model railroading, especially with DCC. Our often long wire runs (15-20ft both ways is not uncommon on a 4x8, double for a larger layout) make the voltage drop issues worse.

    12 AWG 20 amps
    14 AWG 15 amps
    16 AWG 10 amps
    18 AWG 7.5 amps
    20 AWG 5 amps
    22 AWG 3.7 amps
    24 AWG 2.5 amps
  14. Torpedo

    Torpedo Member

    24 AWG is rated for 3.5 amps for chassis wiring and only 1/2 amp for power transmission. The chassis rating is for a single wire not in a bundle (air cooled). The power transmission rating is for bundled wire. Both ratings are very conservative and are mainly concerned with fire protection. They are for continuous current. Pulse operation could be substantially higher.

    The bigger question is this: Is the wire's resistance too high for your application? 24 AWG is roughly 25 ohms per 1000 foot. If you had a switch machine 10 wire feet away from the power supply, for example, you would have 25 * 20\1000, or 0.5 ohms of total wire resistance, which might not hurt anything. On the other hand, if your switch machine was 100 wire feet away, you would have 5 ohms of resistance, which just might be a serious problem.

    How big the problem would be depends on the resistance of the switch machine's coil(s). The swich machine coil resistance would have to be a substantial multiple of the wire resistance in order for the wire resistance not to be an appreciable factor.

    Measure your switch machine's coil resistance using an accurate digital ohmmeter, then divide that by the calculated resistance of the full loop of wire. I suggest a value less than 10 would be entirely unacceptable. 20 or more would be much better, 100 or more would be ideal.
  15. DixonRobertson

    DixonRobertson New Member

    Thanks for the advice.

    I'm at work now (sigh) so the VOM testing will have to wait. Currently (no pun intended) my longest run from panel to turnout is 5' as the crow flies, maybe 7' with turns in the wire. I hope to add a module in the next year that may include turnouts up to 13' as the wire routes. The turnouts are all Atlas snaps; the CDU is from a circuit posted on this site, using a 2200 mF cap and a 24VAC power supply. Remember I was a political science major (decades ago), so anything more complex than long division will challenge me.

  16. Torpedo

    Torpedo Member

    I didn't know they taught punch blocks in Politcal Science. I'll bet most people have never heard of them.

  17. DixonRobertson

    DixonRobertson New Member

    OK, OK, so maybe I cabled my (solo) law office network, and the one that keeps growing at my house as I add replaced computers to it. And hey, if I didn't at least know how to solder what would I be doing in this hobby?
  18. pgandw

    pgandw Active Member

    You should be OK given the relatively short runs. Atlas switch machines are usually in the 12-17 ohm range, which means you could draw as much as 2 amps from a 24 volt supply (other brands of switch machines draw quite a bit more current).

    The weak point is going to be the wire to plug connection at the plugs. Those are generally pretty small contact surfaces. If they start arcing instead of conducting due to poor contact, oxidation, or corrosion causing high resistance, you will have escalating problems until the connection fails.

    just my thoughts
  19. DixonRobertson

    DixonRobertson New Member

    RJ-12 patch panel for turnout wiring

    It works!!!! Thanks for all the comments. My cab has a 24 VAC transformer feeding a CDU. Most turnouts are controlled directly by SPST NO momentaries, some of which throw multiple turnouts. The small ladder yard is controlled with a diode matrix (thanks to a Canadian poster here for the schematic and physical design). Each turnout control wire is punched into an RJ-12 jack mounted in a patch panel that in turn is mounted in the back of the cab box. Under the layout, adjacent to each turnout, is a simple RJ-12 wall-mounted box. My benchwork for this section allows foam without plywood beneath, so the wall boxes mount to the bottom of the foam with two-sided tape. From the patch panel to the wall boxes run varying lengths of Cat-3 cable with RJ-12 jacks crimped on each end.

    When I first hooked everything up it all worked, except for the "thrown" side of one turnout. (I can't remember anything else in my life that worked out so well on the first try--except my daughter, of course.) Turns out (no pun intended) I had reversed one of the jacks when I crimped it. Fixed that, and everything was copacetic.

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