Telephone Ringers: how & why

Floyd,

That is weird. How did a static charge keep that "dry" leased line from working?

By the way -- I see you're in Alaska. Have you ever had any dealings with Witham Reeve?

Bob

What it really was, was a high-resistance splice caused by oxides on the wires. Most any voltage would "seal" it again.

"Don Bowey" wrote" [snip]

Ahhh. I see.

My POTS line gets noisy some times. Maybe because I rarely use it. The best cure seems to be to get my line to ring and then go offhook in the middle of the ringing. It works every time (for a while).

Bob

If the static charge is higher than the signal level... the continuity for signal is zilch. The real cause though is corrosion from dampness and poor insulation at splice boxes and connectors. The corrosion causes various effects (resistance, diode effects, and capacitance) that allow a charge to build up and be maintained at a higher voltage than the signal. At that point, the line goes totally dead. Usually just a lower resistance (for example plugging in a test set on the line) would dump the charge and make it work again. That didn't change the cause though. On the other hand, hitting the line with 100 VAC of 20 Hz ring voltage would often change the electrical characteristics of the corrosion, at least for awhile.

That was not something commonly experienced until the

Which of the 600,000 people in Alaska would Witham Reeve be? And does he live in Los Anchorage, or actually in Alaska? ;-)

It is the oxide flim that form on the wires, but it isn't usually just high resistance in series alone that is the problem, and it would rarely be a (soldered) cable splice. Terminal boxes, with punchdown or the old screw type terminals do indeed get high series resistances, but otherwise there are the other effects shunting the line too.

It used to be that often the lack of VF continuity would be corrected by just putting a test set on the line (which would bleed off any charge on it, and perhaps even zap the corrosion in the process). Sealing current (e.g. 10-15 ma) is not a corrective measure, it prevents the oxide film from forming.

When no sealing current existed, to correct it often required the high voltage (and current) available with ring voltage, which breaks down the oxide film that has formed.

Did anyone ask for a brain dump of what you may know? You didn't say anything I don't know from experience.

I know how static charge works. I recall back in the early 90's we had a freak snow storm that dumped a few feet on the city in a very short time. A friend and I worked emergency communications for the Red Cross.

When the group of us got to the radio room we discoverd that they'd cut off the cable ends on all the coax and because the storm was still blowing you could see the center conductors arcing to the ground braid on all the cables all because of static electricity.

Imagine if we could harvest and store that energy.

So, in other words, you called the cops with your ass? ;-)

Cheers! Rich

Yeah - you have a bad pair. Eventually even ringing it won't help and it'll just stop working.

I recall an incident with Nynex back in the day where my line was absolute crap. Whining, crackling, etc. whenever it was very windy, rainy or both.

Took several months of constant calls to Nynex to fix that one. After it was fixed, every time it would rain or a strong wind would blow they'd contact me to ask if the line was still working.

If there's one thing I am, it's persistent.

Brings new meaning to talking out of ones ass.

If it's the really old kind, with a carbon mic element, just whack the mouthpiece end against the heel of your hand - this will unstick the carbon particles, which is what the ringer is doing now.

Cheers! Rich

Once again I corrected errors in your article. Sorry that upsets you. You'll get used to it.

That might be doing something. But usually a POTS line that is noisy sometimes (often when there is high humidity) and is fixed with ring current, has corrosion (literally green stuff growing) around a terminal somewhere, and that is providing a low resistance to ground.

Stray current to ground that is unequal between the tip and the ring causes noise that has a lot of popping and sounds like a frying pan with hot grease in it.

The ring voltage provides more current than the path to ground can handle, and literally burns it out. For awhile at least, but it will grow back on the next humid day and need another treatment, or get so bad the ring current won't help.

Sometimes that sort of corrosion causes a slightly different problem, called "ring trip". The low resistance path is between tip and ring, and when hit with ring current it starts conducting... and continues to conduct between the ring cycles. The DC loop current then also goes through the corrosion and the extra current makes the line appear to be offhook, which of course stops the line from ringing. Symptoms would be just one, usually abbreviated, ring when someone calls. If the called line is then answered, the calling party is there and they can talk. Sometimes though, the ring is so abbreviated that it isn't even audible. Everyone who calls gets a dead line after one ring and nobody ever answers the phone.

That can sometimes be fixed with a long burst of continuous ring voltage on the line, but it usually requires outside plant to go find the terminals that are corroded and clean them up (and tighten the screws or repunch the punchdowns, to get a better connection).

What do you think you could do with a little static?

You corrected nothing. You just dumped your blog.

Back before the "endless September" arrived, when Usenet was THE place to get answers; an expert on sealing current enlighted us.....

place to

One thing is important to remember, 'sealing current' (which appears to be a new term for what was always known as 'wetting current' as far back as I can remember), was never intended to be a panacea for correcting oxidation of joints in the cable transmission loop. All physical joints in a copper transmission circuit are meant to be 'properly' made so that oxidation at these points is not possible. Of course we all know that sometimes errors and poor workmanship do produce poor joints.

The idea of the wetting current is to overcome oxidation of contacts on interface cards or other equipment which may be interposed in the circuit loop, not on oxidation of joints on the line itself.

That is an interesting observation. As near as I can tell the term "wetting current" is the more commonly used term outside of the telephone industry, or perhaps more specifically whenever the application is something _other_ than a telephone cable.

"Sealing current" seems to be rarely used for anything other than describing the way "wetting current" is applied to telecom cables. And there is it, as far as I know, univerally used. I can't recall ever seeing anything that referred to it as "wetting current" when it was strictly for telecom cable. (I'm sure that somebody somewhere manufactured a device they described using "wetting", but all of the ones I can recall now were describeds as "sealing".)

Basically true, but still there are a lot of "pressure contact" connections made in telecom equipment. That includes screw terminals, punchdown blocks and the ubiquitous wirewrap.

The effects of not using sealing current on a dry cable pair are virtually guaranteed to be encountered too. It isn't some percentage of cables that will be affected, it's *all* of them.

"I was personally the researcher that did the sealing current work while at Bellcore. And you are right on target....sealing current does effectively keep a copper loop intact (through a process called electromigration). I could bore you with all the Material Science theory behind it...but it does work on copper loops which have splices." Brad Bennett, from the above URL

It pretty clearly was intended to maintain copper loops.

Certainly in other industries it is commonly used more often to maintain metal switch contacts, for example.

It is not a deficiency though; it is a physical property of cable pairs, and they will *all* suffer from it sooner or later.

There is no way to "be running around fixing" the problems that sealing current corrects, short of periodically redoing *every* splice in *every* cable. That of course *would* be a very poor engineering practice, given the simple technology (granted that it is not well understood by most) available.

...

In the "old days" there were few cables used that did not have current flowing. The idea that cables were well maintained then and not now is not correct at all (cable was cheaper to replace then than it is now, making maintenance more productive today than it has ever been).

That just is not true. And even if it were true, that would *not* prevent the problem that sealing current solves.

It is mandatory, but not at all for the reasons you surmise.