How to test telephone wire with a multimeter

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Old 12-06-06, 10:40 PM
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How to test telephone wire with a multimeter

Hi all,
A long time ago I posted a problem we had with setting up our DoorKing 1812 gate system with our phone system. I just couldn't get it to work. I finally called in a professional and he said that the line going from the 1812 unit to the Telephone Interface Device had a short. I bought a multimeter and would like to test this out myself just to confirm. I would hate to lay out 100 feet of new telephone wire only to figure out that this wasn't the problem.

How would I do this? I have been searching the web and it says that I need to test for continuity.

There is wiring from the 1812 circuit board to the bypass switch and then wiring from the bypass switch to the Telephone Interface Device. The wire from the 1812 to the bypass is the one that is questionable. What is the proper way to test this wire for continuity? There are 4 wires on this strand. Is it possible that some of the wires are good and some are bad? How do I separate the good ones from the bad ones?

Any help is much appreciated.
 
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Old 12-07-06, 05:34 AM
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Well, the ideal way would be to test each wire individually by metering from one end to the other (to check for a break) and then from each wire to each adjoining wire (to check for a short between wires). Since the wire is 100 feet long that would be impossible, but what you can probably do is disconnect both ends and jumper two wires together to make a loop and then meter between the two wires at the other end. Alternate the wires you jumper until you've covered all possible combinations. With both ends disconnected, you can still meter between individual wires to see if one is shorted to one of the others.
 
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Old 12-07-06, 06:14 AM
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your checking with a meter isn't likely to tell you much , you hired a pro take his advice .

very common for buried cable to go bad ,when you replace the cable to the gate be sure to use direct bury cable
 
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Old 12-07-06, 10:08 AM
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Originally Posted by the_tow_guy View Post
Well, the ideal way would be to test each wire individually by metering from one end to the other (to check for a break) and then from each wire to each adjoining wire (to check for a short between wires). Since the wire is 100 feet long that would be impossible, but what you can probably do is disconnect both ends and jumper two wires together to make a loop and then meter between the two wires at the other end. Alternate the wires you jumper until you've covered all possible combinations. With both ends disconnected, you can still meter between individual wires to see if one is shorted to one of the others.
That's what I will do. What setting do I use on the multimeter? The reason why i want to do this myself is because if I ever have a problem again I will know how to trouble shoot it myself. I just want to learn. Also, the wire from the circuit board to the bypass switch is actually not one contiguous wire. It actually goes from the 1812 circuit board to a box and then from the box to the bypass. So there are actually 2 sections of wire that could possibly be problematic. The wire from the circuit board to the box is buried. The wire from the box to the bypass is not - it is just stapled against the house.
 
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Old 12-07-06, 12:19 PM
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unless you use something like this the test is pretty well meaningless

http://www.datacomtools.com/catalog/tempo-sidekick.htm
 
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Old 12-07-06, 12:22 PM
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A little pricey for the average diy'er. MangoMan is likely right that you may not be able to discern much with your meter, but doesn't hurt to experiment a little. You'll want the continuity scale on the meter; it might beep when you touch the two leads together in that position which is an easy, audible indication that the circuit is closed. Other wise you can use the resistance (ohms) scale and be looking for "some" resistance; "0" or no reading would indicate an open.
 
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Old 12-07-06, 12:58 PM
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point is a VOM just wont find all faults and if a test cant point out all that could be wrong whats the point ?

I have a upper end Fluke VOM and I would never waste my time trying to test cable with it
 
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Old 12-07-06, 03:20 PM
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Originally Posted by the_tow_guy View Post
A little pricey for the average diy'er. MangoMan is likely right that you may not be able to discern much with your meter, but doesn't hurt to experiment a little. You'll want the continuity scale on the meter; it might beep when you touch the two leads together in that position which is an easy, audible indication that the circuit is closed. Other wise you can use the resistance (ohms) scale and be looking for "some" resistance; "0" or no reading would indicate an open.
Ok. I am going to give it a try. I don't need to know exactly what is wrong, just that something is wrong. The guy that came out here to look at it was using a multimeter to test. Does this mean he might not have been completely certain himself that it is the line?
 
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Old 12-07-06, 04:19 PM
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VOM will show you major problems but cable can look OK with the VOM but still have issues that would cause your gate not to function

have fun but this is wasted time from a troubleshooting perspective . suppose your meter tests show no problems

what then ?

you still have a non functional gate .

where do you go then ?

pay somebody else to tell you the cable is bad ?

start replacing expensive components ?

seems like replacing the cable would be the easiest cheapest place to go .


can you go to the gate , put a jack on the cable and get dialtone ?

place a call ?

receive a call ?

is the line clear or does it have static ?

thats how I would test it



(im assuming you have verified that all other components are functional and correctly hooked up )





i
 
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Old 12-07-06, 07:03 PM
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Originally Posted by mango man View Post
can you go to the gate , put a jack on the cable and get dialtone ?

place a call ?

receive a call ?

is the line clear or does it have static ?

thats how I would test it

i
If this is a better test, then I will do it. Do I just get a jack and hook it up to the wires?
 
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Old 12-07-06, 08:01 PM
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disconnect the wires at the gate , wire in a standard phone jack then plug a phone in to test .
 
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Old 12-08-06, 06:10 AM
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In addition to simply wiring in a phone as a check, would something like one of these work, Mango?:

http://www.specialized.net/ecommerce/shop/seriesmaster.asp?series_id=Line+Checkers
 
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Old 12-08-06, 07:09 AM
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no all thats doing is verifying voltage and polarity .

just hooking a phone up verify s voltage with dial tone

polarity hasn't been a issue in years , older equipment was polarity sensitive , newer stuff has polarity guards built in

radio shack sells one for 5.00

http://www.radioshack.com/product/index.jsp?productId=2103388&cp=&origkw=phone+tester&kw=phone+tester&parentPage=search

its handy to tell weather your phone or jack is bad (assuming you dont have a known good phone to plug in )
 
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Old 12-08-06, 10:22 AM
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Based on the low price I was guessing you wouldn't get much more aid in troubleshooting than you would by plugging in a phone and listening for dial tone and/or static.
 
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Old 12-09-06, 08:48 AM
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You should be able to test this with your multimeter just fine. Just check the impedence (Ohms) from one end to the other. The suggestion to unhook all four wires and hook two together at one end to form a loop is a good idea. You could also use a second exterior wire that would span the distance to form your loop. Test your wire first and note the impedence across it. Your phone wires should not add much to it when in the loop. If it does I would say you definately have a problem.

If you use the internal wires themselves to create your loop on one end take them all apart at both ends first and test between them at both ends. You should see an open circut.

Using the phone would also help but phones only use two of the wires and I think it would take you more time to hook it all up and switch between wires than just to use your multimeter.

As one poster said your pro probably did just this and found a break somewhere or a short between a couple of wires, but I understand you wanting to check it for yourself.

I would not purchase anything more than a simple meter to test this.

My two cents!

Best of luck
 
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Old 12-09-06, 09:12 AM
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If it was me I would disconnect all the wires at one end. Go to the other end and test for shorts between all the combinations.
If no shorts then connect all the wires together at one end and test for opens.
 
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