telephone wiring (lightning)

[Matthew]

Had a serious batch of storms roll through last night, heard a pop, now one of our telephone outlets has failed.

At first I thought it was dead, but I can actually hear the dial tone (it is just extremely faint, barely audible.) I have an old ATT touch-tone phone with a light-up key pad I use as a tester, keypad lights up, and am able to dial, just that the volume is extremely low (only on that outlet).

Checked the wiring where the other lines are connected at the incoming junction in the basement, and didn't see any sign of arcing. Next step is to replace the wall jack.

I haven't dug out my meter yet, and the other three jacks in the house work fine.

Anybody have any experience or ideas on just how/what may have happened?

 

[mikea]

Had a serious batch of storms roll through last night, heard a pop, now one of our telephone outlets has failed.

At first I thought it was dead, but I can actually hear the dial tone (it is just extremely faint, barely audible.) I have an old ATT touch-tone phone with a light-up key pad I use as a tester, keypad lights up, and am able to dial, just that the volume is extremely low (only on that outlet).

Checked the wiring where the other lines are connected at the incoming junction in the basement, and didn't see any sign of arcing. Next step is to replace the wall jack.

I haven't dug out my meter yet, and the other three jacks in the house work fine.

Anybody have any experience or ideas on just how/what may have happened?

Is it really only one jack that's dead? That would be weird.

Obviously, if you see burn marks at the jack, you can disregard all of the following investigative technique.

There is lightning protection at the IT (inside terminal) on the phone company's side. They will have carbon fuses with a actual metal spring that shorts the lines to ground when the carbon vaporizes. As you can imagine it's very slow to work.

If the carbons fired all of your phones would be grounded and you'd have to get telephone repair service to replace the carbons. That's NOT inside wiring so you should not get a bill. If you have to call for service make it clear that the line is dead when it comes into the house.

More recent phone installs will have a RJ-11 jack at the I.T. where you can plug in phone to check if it's dead there.

If it really is just the one jack, check the wiring back to the junction, but it may really be you need to replace the jack.

 

[Matthew]

It's just the one jack. That's where I heard the 'pop'. I planned on replacing it tonight. I was curious as to how I'd be able to hear (very, very faintly) a dial tone. I'd think either it would work, or not work, and not be somewhere in between. I didn't have time to do much poking around last night or this morning.

The main line comes inside the house into the basement, then to a board where the 4 interior lines originate. All connections on that board look good and no evidence of arc.

I'm guessing I'll see the soot inside the suspect wall jack when I take it apart. Actually, I'm HOPING I see the soot. I'd hate to find out there's a break in the line somewhere between the basement and the 2nd floor. No way I can fish that through.

 

[mikea]

It's just the one jack. That's where I heard the 'pop'. I planned on replacing it tonight. I was curious as to how I'd be able to hear (very, very faintly) a dial tone. I'd think either it would work, or not work, and not be somewhere in between. I didn't have time to do much poking around last night or this morning.

The main line comes inside the house into the basement, then to a board where the 4 interior lines originate. All connections on that board look good and no evidence of arc.

I'm guessing I'll see the soot inside the suspect wall jack when I take it apart. Actually, I'm HOPING I see the soot. I'd hate to find out there's a break in the line somewhere between the basement and the 2nd floor. No way I can fish that through.

You can hear a faint dial tone if one or both sides is open and/or shorted to ground.

 

[gismo]

You can hear a faint dial tone if one or both sides is open and/or shorted to ground.

Not really. The phone line consists of two conductors labled "tip" and "ring" which come from the days when all calls were routed manually on a plugboard using three conductor plugs whose terminals were "tip", "ring", and "sleeve" (tip was... well at the tip, ring was the band next to the tip and sleeve was the rest). To draw dialtone there must be a current path between ring and tip or ground (earth). The voltage supply is nearly 50 VDC and IIRC you need several milliamps of current to get a dialtone. Unless you have a payphone, your instument places a load between tip and ring to "start" the line and get a dialtone. If the tip side of the line was shorted to ground you would get something similar to your problem except that all the phones would be affected even if the short was at the jack that doesn't work in your case. You'd also get a fairly loud hum as the short would unbalance the line.

Chances are a connection on that jack's circuit has developed some resistance. The most likely place is at the jack or wherever the line to that jack connects to the rest of the system. That could be at the network interface if you have one, the protector (an odd shaped black thing with brass studs and nuts), or another jack.

You can confirm this with a meter. With no off hook phones connected you should get 48-50 VDC between the two wires (tip will be the positive one). Switching the meter to amps you should measure something between 50 and 100 ma (I think that's the right value but you could compare it with a jack that works). If the current is much less than 50 (probably less than 10) you have a bad connection. To confirm go to the network interface or protector and short both sides of the line to ground (this will disable all the phones but won't hurt anything). If you have the network interface you can unplug the house circuits and just short them (the plug side) to ground, if you just have a protector, I'd leave the wires conected and just jumper them to the ground stud. Then go back to your bad jack and measure the resistance between each lead to a nearby ground like an outlet safety ground. The resistance should be no more than a few ohms.

 

[Matthew]

D'oh. (Insert image of me smacking my forehead with the heel of my palm)

Note to self: When testing a phone jack, make sure the corded phone you dug out of the closet wasn't tossed into the closet because it doesn't work anymore.

I verified the other extensions worked by simply picking up the phones already attached. We have a cordless extension upstairs, and rather than disconnect the phone/answering machine combo from downstairs and dragging it up, I just used our old corded phone that I stashed away some time ago.

I did take apart the jack and see the voltage with my old Micronta meter (that's what allowed the keypad to light up and make me think the phone was good). I didn't measure the current, maybe I'll do that just for fun.

By the way, the 'pop' I heard must have come from the modem that was connected to the questionable phone jack. Another trip to Best Buy and I should be back in bidness. The modem goes through all self-checks, but does not detect a dial-tone. The test phone barely registers the tone, so I put apple and oranges together and came up with 3. Oh well, it's the best I could do in the 10 minutes I had time for that night.

Something definitely got into the house that night.

Another note to self: When you get a high-dollar UPS for the computer, and it includes a protected phone jack, go ahead and use it.