# Pressurized telephone cables?



## chewy

Dnkldorf said:


> What's the sense behind pressurizing the telephone cable coming into the demarc, inside a building? I can't figure it out.
> 
> Telephone cable, I dunno, maybe 200 pair, comes into building to the IT room.
> 
> About 2' before the casket looking j-box thingy, there is a air fitting and on the casket there is another. I assume they pressurize it for some reason?
> 
> Why, inside the building?
> 
> I can see why on a pole outside, but inside?
> 
> Anyone know why?


Never heard of that before? Any chance you can take a pic for me if security allows it?


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## 10492

I am googling an image right now. I think they called them telephone cabinets.


2 piece cast aluminum, with seals for the cables coming in and out. 3/8" bolts all around it, hold it shut.


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## chewy

Dnkldorf said:


> I am googling an image right now. I think they called them telephone cabinets.
> 
> 2 piece cast aluminum, with seals for the cables coming in and out. 3/8" bolts all around it, hold it shut.


That actually rings a bell for underwater cable laying but not in modern times, how old is it?


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## 10492

chewy said:


> how old is it?


No clue.....don't know much about telephone stuff...


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## jw0445

It's old cable, probably air core pic or stalpeth (paper insulated). Alot of manhole and vault cables had air on them to keep the water out and a compressor or canned air to keep the pressure at a couple of pounds. Is it black plastic or lead covered? Just curious.


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## Big John

I don't know if it's still done, but older cable was definitely pressurized with dry air to prevent corrosion form moisture intrusion and preserve the cable.

A buddy of mine used to do that work for Ma Bell: If they had loss of pressure on a line they knew they had a leak somewhere, and he'd have to run around listening for it. I think he used an ultrasonic amplifier.


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## Southeast Power

Dnkldorf said:


> What's the sense behind pressurizing the telephone cable coming into the demarc, inside a building? I can't figure it out.
> 
> 
> Telephone cable, I dunno, maybe 200 pair, comes into building to the IT room.
> 
> About 2' before the casket looking j-box thingy, there is a air fitting and on the casket there is another. I assume they pressurize it for some reason?
> 
> Why, inside the building?
> 
> I can see why on a pole outside, but inside?
> 
> Anyone know why?


There was a rig down the street from us when I was a kid. It had a tank chained to the pole and connected to the cable..
Thought it was fun to let the air out of the valve. It was like the one on our bike tires.


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## millelec

had an underground heating pipe spring a leak, 5000 gallons per day of 200 degree hot water. got into communications pit, and melted outer covering on phone cable. they came looking because lost air pressure. was prolly about 10 years ago.


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## randas

I've seen it done for tamper detection. Pipe looses pressure alarm goes off


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## SteveBayshore

I used to work in some old AT&T and Ma Bell switching stations.
Old lead sheathed communication cables had paper insulation on the individual conductors. Any moisture inside of the sheath would cause havoc. All taps and joints in the sheath were lead solder sealed. The cables were pressurized at the switching stations and monitored for loss of pressure. If pressure loss was evident, bottles of nitrogen were placed at various locations in the cable until the leak could be found and repaired. These were the high pressure cylinders you used to see strapped to the telephone poles.


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## Ty Wrapp

Dnkldorf said:


> I am googling an image right now. I think they called them telephone cabinets.
> 
> 
> 2 piece cast aluminum, with seals for the cables coming in and out. 3/8" bolts all around it, hold it shut.


Preform Splice Case...


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## TOOL_5150

ive dealt with the lead covered pressurized cables. they usually have paper wraped conductors, so you wouldnt want moisture in them, which is why they are pressurized.


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## big city

*Air pressure*

First post here! The air pressure in our area is around 5 psi...keeps moisture out. We dispatch on low pressure alarms, have pulp pic and paper. Wiping lead sleeves is a lost art.....not to many phoneman able to do this anymore. We use helium on direct buried cables under pressure to detect leaks!! Good work, most of the time spent in manholes. There is still alot of paper cable out there, although some being replaced with fiber. 

Those metal cases can be a SOB sometimes. 

If the cable is coming into a building, it should have a plug on it to restrict air flow...it may be that it is a case that justs has the fittings on it.

Trust me if you open it and there is pressure on it, somebody from telco will be out soon.

Please ask away...been doing this for 16 years:thumbsup:


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## five.five-six

to keep water out


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## Ty Wrapp

big city said:


> We use *helium* on direct buried cables under pressure to detect leaks!!
> Please ask away...been doing this for 16 years.
> 
> Helium...are you sure? We use nitrogen.


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## 10492

Here are the pics.










And a close up of the cable that gets pressurized?


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## Big John

Ty Wrapp said:


> ...Helium...are you sure? We use nitrogen.


 For my line of work we use helium for leak detection because there are handheld testers that can pinpoint the source.

With nitrogen it seems like the only option would be listening for it?

Do they still pressurize new cables, or is that an old technology?


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## ralpha494

They had a really informative demo on PBS's documentary on the aftermath of Sandy on this same subject.
The fuel pump for the generator flooded, the generator stopped, and the compressor lost power. The cables filled with flood water, and they had replace all the cables so they went to fiber. Took them several months but they got it done.


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## Ty Wrapp

Big John said:


> Do they still pressurize new cables, or is that an old technology?


New cables are Plastic Insulated Cable (PIC), filled with a water repellant gel. No way for air to flow thru. 

Old cables were pulp (paper) insulated and lead sheath. Any leak in the lead sheath would allow water to saturate the pulp insulation causing multiple faults. Air pressure was added to keep the paper insulation dry.


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## Ty Wrapp

Big John said:


> For my line of work we use helium for leak detection because there are handheld testers that can pinpoint the source.
> 
> With nitrogen it seems like the only option would be listening for it?


Schrader valves at every terminal and a air gauge will pinpoint a section.


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## jconn

*Its a pressure dam*

Its a pressurized entrance cable that is most likely "air core pic cable that travels through conduit from a manhole or "pullbox'. Most underground cable is pressurized even to to DMARC. If you'll notice, that's a "pressure Dam" placed ABOVE the valve to stop air flow at the bldg Terminal. Its all precautionary.Its been know that some splicers fail to put a Dam at Bldg terms and becomes a leak source.


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## Ty Wrapp

jconn said:


> "air core pic cable that travels through conduit from a manhole or "pullbox'. Most underground cable is pressurized even to to DMARC. quote]
> 
> Air core should not be underground :no:


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## jconn

Ty Wrapp said:


> jconn said:
> 
> 
> 
> "air core pic cable that travels through conduit from a manhole or "pullbox'. Most underground cable is pressurized even to to DMARC. quote]
> 
> Air core should not be underground :no:
> 
> 
> 
> Hey TY!
> 
> In most telco lingo Underground means beneath the street/ ground through conduit, which pressurized air core cable is everywhere!
> 
> "Direct Buried" which is beneath grade but without conduit,then yes should not be Air Core!
Click to expand...


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