Simple but vexing electrical engineering question

Most of that kind of wire has some distinguishing mark on it. Sometimes the wire is silver on one and copper colored on the other. Sometimes there are tiny red threads running thru one wire. And, sometimes there is a raise edge on one side of the zip cord.

In lieu of any of this, use an ohm meter once you have it routed and measure which wire is which...alternatively, you can strip one side a half inch and not the other...and determine which is which on the far end.

You can use a battery or any other source of DC. If you use a battery mark the lead that goes to the Plus battery terminal. If you use a Power Pak or similar use a voltmeter to determine which lead is plus. Then go to the other end of the wire and use your voltmeter to determine which lead is plus and mark that. 

Pete

Paul,

   1st with a big layout I would definitely be using multi strand wire, my preference is 14 Gauge although many use the 16.  It almost sounds like you have some older single strand 16 gauge wire, if you do, I would only use it for my Legacy runs, not DCS.  IMO it's better to use the stranded 16 or 14 Gauge wire for DCS layouts.

PCRR/Dave

Use the continuity feature on your multimeter. Connect one probe to a wire at the transformer end and the other probe to a wire at the other end. If you get the audible beep you can connect one end to middle rail and the other to the "hot" terminal on the transformer or alternatively.... outer rail and U terminal.

Roger

cjack posted:

.... And, sometimes there is a raise edge on one side of the zip cord.

...

this is the most common indication i've seen on plain brown zip cord.
put your fingers on either side of the wire, one side should feel rough, one side smooth.

I like Pete's answer, it's positive and works no matter what characteristics the wire has.

Guys, I am electronically challenged. I have a volt/amp meter but don't understand what you're saying to do? It has two probes - how do you do this? I guess I have to make sure the meter has a working battery, first, right?

I cannot tell one side of the wire from the other - other than it is copper stranded.

Dave: it is stranded copper wire - seems to be 16 gauge at least - may in fact be 14.

Set the meter on Ohms, and touch one probe to one end and the other probe to the far end to identify a continuous wire. The ohms will be infinite on the wrong wire and very low, a few ohms on the continuous wire.

The ohmmeter method is fine if you can reach both ends of the cable with your meter. If the wire is on a reel then you might have unroll it to get to the other end. The voltmeter and battery method allows you keep the wire on the reel for easier running and determine which conductor is which after the wire is in place. It would work even if the ends were multiple city blocks apart.

BTW Paul if this wire is common lamp cord then indeed like Chuck says they will be already marked. One side may be smooth all around and the other side will have a small raised ridge. Check closely.

Pete

Can you post a picture of your voltmeter and one end of the wire?  All voltmeters are different and we could give you a very specific step by step if we saw YOUR voltmeter.

Banjoflyer Mark's instructions are very good (if you have access to both ends, i.e. before you run it through the wall).  If not, I can write up step-by-step for either the battery or the continuity to ground method if still needed after all the previous posts.

PCRR/Dave makes a good point.  Running O Gauge, 80' is too long a run to use 16-gauge wire.  I would use 14-gauge stranded THHC wire.  Voltage loss is a critical factor when running low voltages.

John D. posted:

Can you post a picture of your voltmeter and one end of the wire?  All voltmeters are different and we could give you a very specific step by step if we saw YOUR voltmeter.

Banjoflyer Mark's instructions are very good (if you have access to both ends, i.e. before you run it through the wall).  If not, I can write up step-by-step for either the battery or the continuity to ground method if still needed after all the previous posts.

John, every multimeter I have come across going back over 50 years comes with one red lead and one black lead. The red lead should be plugged into the hot terminal and the black into the common. Digital meters display postive and negative numbers. Analog meters only show positive numbers so if the needle tries to move below zero you have to reverse the probes. If you attach your wires on to any battery, mark which lead is attached to the plus and minus then go to the other end of the wire and put your voltmeter leads across the two wires, if your meter reads a positive voltage then you mark the wire the red lead is touching as positive. If you voltmeter reads a negative voltage you mark the wire that the black probe is touching as positive. If you reverse the probes so that the red lead is on the wire you just marked positive then the voltage will also be reading a positive number.

Pete

While everyone has good suggestions, I would connect the wire as usual at the control end, whether that's to a TIU or transformer, or what have you.  Assuming there is live track somewhere near the other end of the wire, even if it has significantly dropped voltage, I'd then use an AC volt meter connected between one rail and one of the two wires.  No voltage?  connect that rail to that wire.  Some voltage?  The other wire connects to that rail.  

JGL

Thanks everyone. I have to get a new battery for the meter - haven't used it in at least 10 years - and will give this a try. Pete, I'll try the battery method if I can get the meter to work. I'll see if I can take a photo of the wire, too.

Norton posted:

John D. posted:

Can you post a picture of your voltmeter and one end of the wire?  All voltmeters are different and we could give you a very specific step by step if we saw YOUR voltmeter.

Banjoflyer Mark's instructions are very good (if you have access to both ends, i.e. before you run it through the wall).  If not, I can write up step-by-step for either the battery or the continuity to ground method if still needed after all the previous posts.

John, every multimeter I have come across going back over 50 years comes with one red lead and one black lead. The red lead should be plugged into the hot terminal and the black into the common. Digital meters display postive and negative numbers. Analog meters only show positive numbers so if the needle tries to move below zero you have to reverse the probes. If you attach your wires on to any battery, mark which lead is attached to the plus and minus then go to the other end of the wire and put your voltmeter leads across the two wires, if your meter reads a positive voltage then you mark the wire the red lead is touching as positive. If you voltmeter reads a negative voltage you mark the wire that the black probe is touching as positive. If you reverse the probes so that the red lead is on the wire you just marked positive then the voltage will also be reading a positive number.

Pete

The knobs/dials/selectors are different and I thought it would be helpful to use a picture of his voltmeter to show him which selection to use for each of the methods above.  The symbols can be tricky.  I've been designing electronics for 10 years as a mechanical engineer, and I would still be a little lost with another person's DMM.

By the way, my DMM has THREE places to hook up the red lead.  Only one will work for reading voltage and continuity...

John, you are over thinking this. Set the multimeter to DC volts in a range suitable for the battery you are using assuming its not an auto ranging meter.

If you know how to read the voltage of battery whether it be a 1.5v, 3v, 9v, or 12v you can read the voltage at the end of a wire. No difference.

Pete

Norton posted:

John, you are over thinking this. Set the multimeter to DC volts in a range suitable for the battery you are using

 I was reacting to this:

Paul (Original Poster) posted:

Guys, I am electronically challenged. I have a volt/amp meter but don't understand what you're saying to do? It has two probes - how do you do this?

Paul, if I've offended you or not given you enough credit, I humbly apologize. If you would like me to make you a pictorial step by step for any of the above methods, my offer still stands.

I think I achieved success using my meter...it only took one AA battery - I set it to "RX1" Ohms. It was confusing at first because it defaults to infinite Ohms at rest - so I calibrated like Mark instructed - and proceeded to connect probes to ends of wire. Thus, and correct me if I don't understand, when probes are connected to both ends of continuous wire Ohms was zero or thereabouts, and when probes were connected to different ends of different wire Ohms spiked. I guess this is intuitive since Ohms is measure of resistance and thus there would be little or no resistance when probes are connected to the same wire?

Picture shows meter spiking when probes were connected to ends of different wire - on my meter zero is on right side. Brown wire in question is on right side of picture - looks just like lamp wire. I put tape on the same wires to tell them apart, but I'll paint them.

BTW: I closely examined the brown wire and I cannot tell any distinguishable difference between the two strands. I forget where I bought it ~ 15 years ago - but I figure its around $50 of copper wire ~ 170 feet in two 85 foot lengths, so I'll use it. Some speaker wire sold today has one strand aluminum and one strand copper - I suppose for ease of telling polarity.

Thanks again, and correct me if I am wrong on any of my conclusions.

Great...it's used to be not aluminum in the  new wire but tin plated on one side I think. Although a lot of wire is now copper clad aluminum to save copper costs. And, it is almost not stated in the manufacturers' wire description...especially on ebay. You have to watch that because the resistance is higher and requires you to go down a gauge number or so to be equivalent to the all copper gauge resistance.

If it is truly like lamp cord and can be separated like lamp cord, pull it apart and make two single wires.  Then mark each end of one wire with a Sharpie mark to signify it. 

It is better not to run ac wires in close pairs at higher voltages of say 110v due to possible induction between wires.

Charlie

"It is better not to run ac wires in close pairs at higher voltages of say 110v due to possible induction between wires."

W H A T ? ? ? 

When you run a zip cord, the ac current resultant fields would fact cancel themselves between the two wires. And running two intact zip cords together is therefore a non problem if one was worried about inducing noise, each in the other complete zip cord. Now if one runs a single wire with a strong ac current flowing in it next to a data wire or some such, there could be an issue. So what Charlie pointed out can be real, but probably not a problem here.

One more thought:  While you have solved the immediate problem of which wire is which, you do need to permanently and visibly mark them.  Since it's always more difficult to see under the layout, you might want to seriously think about using color coded zipcord (red / black).  And 14 gauge is also a good idea.  A number of vendors make this (Google it).

I understand the temptation to use whatever wire is lying around, but that is a false economy.  I color code and label my wires with tags and I have a wiring plan, and it's still hard to tell what goes where when you are under the layout.

Food for thought.

George

Induction

I ran paired 18 ga lamp zip cord wires to each Marx 1590 switch, one for the straight solenoid and one for the curve solenoid for each switch.  The ground was not included in this run as I use a common ground for the layout and the switch motor was grounded with the track common.  I use 14 vac for switches and have a home rewound transformer used only for the 27 switches on the layout.  The switches did not work correctly when the button was pushed.  I separated all the wires on the lamp zip cord and keep them a few inches apart and everything worked fine.  The problem was worst on the longer runs.  Induction would be worse for 110vac.

Charlie