Home phone lines short, low resistance

stinkytigerSeptember 5, 2012


I was trying to phone home and was always getting the engaged tone.

Got home and discovered that the phone line to the house from Verizon was OK. I plugged in a "basic" phone at the house junction box and got a tone.

I disconnected all the phone pairs coming in and tested eash one. All where open circuit except for one which had a resistance of about 129 ohms. This was the one that was causing the line to get the engaged tone. I removed that one and and reconnected the others, and everything worked. I have one line, not sure where it goes to, which is not connnected.

Can someone tell me:

1) What could cause such a low resistance "short" in a line not connect to anything? I removed all phones etc.

2) How can I trace / track the line to the other end of it so that I can investigate further.

Best, Mike.

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Based on experience, I'd suspect corrosion in an outdoor telephone jack, or even one located in a garage. You may want to look around around a little. Also keep in mind rodents enjoy chewing on exposed wiring.

To trace a hidden wire you usually use a tone generator & amplified probe to follow it - unfortunately "short" at the end may attenuate the tone too much for it to work for you.

    Bookmark   September 5, 2012 at 6:08PM
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Ron Natalie

Last time I had a problem like that, I found that one of my girlfriend's cats had pissed on the terminal block under the desk in her office.

    Bookmark   September 5, 2012 at 7:28PM
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LOL - damn cats. Agree, check the fittings. Also, if it's a punch-down, it may not have been completely punched down and a little push on it may fix it. Any junction is a possible issue, also it's possible there's moisture in that line, or a screw or nail penetrated it. Sometimes these things don't show up straight away.

    Bookmark   September 10, 2012 at 2:55PM
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A very common repair is to isolate the bad line section and then just run a new lone.

The time and effort to find a defect that is not easily accessible is just not worth the effort.

    Bookmark   September 11, 2012 at 10:11AM
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Assuming running a new line is an option, sure.

    Bookmark   September 11, 2012 at 2:11PM
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"Assuming running a new line is an option, sure."

Running a new line is just about always an option.

Folks have been adding phone jacks for at least the past 50 years or more.

It used to be a big deal when the TELCO claimed they owned the inside wiring, and would bill by phones.

They could go so far as to measure the ring current and determine how many phones the line was feeding.

Electronic ringers put a real crimp in that (or anyone that disconnected the ringer on the 'extra' phones.

    Bookmark   September 11, 2012 at 2:50PM
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Given the motivation, anyone can do just about anything, if they're prepared to go to the trouble and expense.

If upstairs and downstairs are all finished, it's going to be pretty difficult. As an alarm tech I think I know most of the ways you can run wires in a retrofit.

Stinkytiger, here's a really easy thing to try no-one's suggested yet: assuming you don't want to run a new wire just yet, and you've eliminated the connections at both ends as a culprit, you could try switching to another pair of wires.

If it's station z old school, line one is probably on red/green. There should be two more, yellow/black. At both ends, put the yellow/black where the red/green was. If it's ok, you're golden.

If it's cat 3 or cat 5, you'll have 4 pairs. Line one is Blue/white blue, line two is orange/white orange. Try removing blue/white at both ends, use orange pair. You can try all the pairs, in fact before you do anything, test the spare pairs with your meter.

Assuming you're not running a business or off-track betting at your place, you're only going to need one line.

    Bookmark   September 12, 2012 at 4:47PM
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Thank you for all your kind help.

The "solution" I went for was to disconnect the offending line. Which jack in which room that line connects to I have no idea. All the phone connect points that I use are working, so no difference for me right now. I have maybe 10 lines from all the bedrooms, garage etc. so am in no hurry to find out which one it is.

At some point in the future I may need *that* line. In which case I will have to struggle with it. Fortunately I think the cable is CAT 5, so I could try another cable pair.

Thanks again for all your kind help.

Warmest regards, Mike.

    Bookmark   September 12, 2012 at 5:24PM
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If, in the future, you do need to locate the other termination point of that line, you could use a good quality network cable tester with TDR built-in on one of the other pairs - it'll at least give you the cable length and may provide a clue in figuring where it goes.

    Bookmark   September 13, 2012 at 9:23PM
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I haven't seen one of those testers before. Pretty sweet, but not cheap.

A regular toner, especially a prosumer model would at least allow you to trace it, and cost If the line's not required and problem solved, it's probably not worth pursuing. It might have been an unterminated spare run somewhere, or perhaps even run for an alarm panel.

Some phone techs get a bit zealous and connect everything in sight, even though, typically, the alarm tech doesn't want their line punched down with everything else, because they want line seizure.

I just saw that Leviton make a really neat phone module for a structured media panel that has a jack ready to go for an alarm panel. Kind of neat, and gives line seizure.

    Bookmark   September 14, 2012 at 2:09AM
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