Telephone Ringers: how & why

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.

There are sporadic news items about departments here and there that are installing the equipment "as we speak". I guess 911 calls from call phones are a real problem, especially when the person doesn't know where he is, probably because he refused to ask for directions. ;-)

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.....

Don ---

If you knew 1/1000th of what Floyd Davidson has learned over the course of his telecom career, you'd be considered quite knowledgeable.

Sadly, the latter doesn't seem to be the case.

He never insulted you or acted rudely to you. All he did was try to answer the original question in a factual manner and expand upon some aspects of it in a constructive fashion which are of interest to many of us (if not to you). Please try to return the courtesy in the future.

FO

Ah... a well thought out constructive response.

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.

far

I spent 37 years in the telephone industry and when I went through training school in 1956 - 60 were were taught that it was "wetting current", but as you say, that was in relation to switches, contacts etc, not line plant. To my knowledge there was no need to prevent oxidation on a copper pair circuit because all joints were made properly. If they weren't solid then they had to be made so, and a quick fix of using a "sealing current" to overcome deficiencies in line plant was 'not on'.

Line plant pairs that required protection from oxidation were in dry air or gas filled cables.

I notice that CISCO use the term 'wetting current' in the documentation for their WAN cards.

Of

I have had a re-think on the whole issue in the light of current practise and I have come around to agree with your thinking.

From memory, when we did our introduction to insulation displacement terminations (by both L.M. Ericsson, Krone and others) the information was that IDS joints were gas tight and oxidation at the knife contact points did not occur. The same was the case for wire-wrap on square posts. Of course any joint is only as good as the workmanship and the use of the correct tools to make them. Most of the joints of whatever type would also have carried some DC component which would have masked the effects of any oxidation which did occur, so this defect would not have become obvious.

I agree, more copper pairs in use today are used for circuits which carry no DC component at all and if there are joints which are not well made then the use of a wetting or sealing current will aid in overcoming the deficiencies in those cases. In today's cut-throat world most telco's don't want to be running around fixing the old copper cable plant just to make a better connection so they will rely more and more on the cover-up use of devices which supply wetting or sealing currents. Not really good engineering practice in my opinion, but that's the economic bottom line today.

I remember many years ago that 3M were touting a new cable gel sealant to Telstra so that they would rarely have to open cable joints ever again. After a few years in service it was discovered that the gel had actually absorbed moisture and all the joints where it was used started corroding.

Well it probably became the intention mainly due to the cost of maintaining copper cable plant and the reticence of telco's to carry out the work necessary to maintain the plant in good order. In the old days the cable plant would have been fixed when it started to display evidence of variable or high resistance. Any cable loops which did not employ a DC component to provide a wetting or sealing current would usually be carried in pressurised cables. But of course, there are many more circuits in use today which don't have a DC component and which can't be provided in a pressurised cable so I agree that in this environment the use of wetting or sealing cureent on line plant circuits is almost mandatory these days.

Yes, it is mandatory to arrange for wetting current to be provided where relay/switch contacts carry only low level ac signals.

I can see that it was probably necessary to devise the term "sealing current" where it applied to copper line plant in order to distinguish it from the "wetting current" which was generally used to describe the use of a small DC current on local circuits within a piece of telephone equipment. Overall, there is some sense to the use of both terms but I just hadn't heard of the term "sealing current" in relation to telephony line plant circuits. In my day "wetting current' was used to describe local application as well as on line plant.

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.

T wrote in news:MPG.21437710ce5e9d3898a214 @news.east.cox.net:

I got bit by stactic discharge during a hailstorm, when I was unlugging my radio gear.

It would be impractical to collect, store, and convert.

I'm fully aware of those facts. All I'm trying to say is that there's a lot of energy floating around out there that we can't even begin to tap into.

Another aspect.... sealing current implies DC continuity.

That makes craft level loop testing far easier. Larry Lippman made a long post detailing the various bridges [Whetstone, etc] the Test Board used to find where the fault was, but I can't find it in the Google archives.

So, are you telling me that all Arizona 911-centers are fully equipped to locate a caller with GPS?

Please note that just because a telephone set has a capability doesn't mean the 911-center has the capability. You need both.