phone company data line voltage

[don_resqcapt19]

We cut a 300 pair phone line because the locator missed the cable by ~20'. When the phone guys came out, I told them I got a little tingle when I brushed against the bare end. He told me that you have to be careful, some of the high capacity data circuits have 260 volts between the conductors!!!
Don

 

[celtic]

Hope you're ok.

 

[mdshunk]

I don't know the real answer, but it sounds like smack to me. I know phone lines ring near 100 volts, and talk voltage is near 48 volts. It confounds me why data would ever need anything higher. It will be interesting to learn the real answer, which is sure to shortly follow...

 

[zbang]

Fast enough?
He's right. POTS lines are ~48v open circuit and ~100v for ringing, but data circuits with mid-span repeaters often use +-130v (or 260v PP).

 

[jrdsg]

locator error

locator error

Consider yourself lucky it was an easy to splice telco cable. Recently a contractor working on the street near my home hit a crude oil pipeline. There was a 40' high geyser that pumped copious quantities of oil into the nearby neighborhood, covering cars, lawns, etc., and eventually running down the hill to the shoreline of the inlet below. The various parties are still pointing fingers at each other while the people in the neighborhood live with the toxic aftermath.

I wonder what kind of telco line would run 200V or more, or for what reason. Most high-speed data [faster than ADSL] is fiber.

Even a low-current hit at 200+ volts could be bad for you under certain circumstances.

 

[don_resqcapt19]

I am fine, but was not really thinking about the possibility of a serious shock hazard from a phone cable. That was the real reason for the post...to make others aware that there can be dangerous voltage levels on phone cables. Had I known that there could be that much voltage, I would have got my gloves before moving the cable out of the way so we could finish out ditch. It was just a little tingle and I have no idea if it was the 48 volt dc from the POTS pairs or the + - 130 for the T1 pairs. The biggest issue was that my customer was out of phone and data service and because of the extensive use of an off site server for logon and security verification even communication between computers on the site was affected. When I cut the cable yesterday, the main T1 was still up...in a different cable...after the phone company started working on the break we lost the main T1. Phone company said it had nothing to do with there work, but I am not sure. The cable I cut had the backup T1 and that was restored about 2pm this afternoon...almost 24 hours after the dig in.
When I called the phone company, they told me that they couldn't even send any one out to look at the problem unless the actual customer called. I said "lady, this is a 300 pair cable and I am sure there are outages, but no, I had to get the plant people to call in outages and they still didn't get anyone on site until 12 hours after my first call. The cable splicer wasn't too happy...he said now that the phone company has contracted a third party locating service they have a lot more cut cables because of mismarking.
Don

 

[don_resqcapt19]

The various parties are still pointing fingers at each other ...

At least I don't have the finger pointing problem. The locating company said that they missed the mark. I did call my office and had someone run a camera out so that we could document where we dug up the cable and where the locate marks were.
Don

 

[dereckbc]

Don I can answer your question. Telco's use two battery voltages 48 VDC and 130 VDC.

The 48 VDC is used for every POTS line and is known as talk battery to supply power to the ole 500 sets. It is current limited at the switch so if you were to short it out on the back of th eswitch it would supply 60 milli-amps max. The further you get away from the office, the less current it is able to supply

The 130 battery supply is for T1 repeater circuits. It operates a little differently in that it is a 10 milli-amp current supply up to 130 VDC. T1 cicuits have to have a device called a repeater about every 5000 to 6000 cable feet before the signal degrades and needs regenerated. The 10-ma current is ran though a zener diode at each repeater to supply approx a 10 volt power source for the repeater circuitry. The only way to measure or see the 130 volts is to open the circuit like cutting the cable. The reason for the higher voltage is to overcome voltage drop over very long T1 which in most cases is only between telephone offices on what is called Trunk Cables. The standard T1 spans for buisnesses and customer use the standard 48 VDC supply limited to 10-ma.

So the only way to see 130 VDC is to cut a CO trunk cable. There are not many left now days because Fiber has replaced just about all the copper T1 trunk cables.

 

[hbiss]

There are still a lot of copper T1s out there. To put it simply the power for the repeaters and the terminal unit at the customer's premises is supplied on the two pairs and is constant current.

We are all used to constant voltage systems where the voltage stays the same as the current increases or decreases. With constant current the opposite is true- the current stays the same as the voltage increases or decreases to maintain a fixed current value. (Think of the old series string street lights). This is done to automatically compensate for varying loop lengths. The voltage will increase or decrease from the CO depending on the series resistance of the copper wire supplying the device to maintain 10Ma through the loop and the device.

Obviously then if the device (repeater or terminal unit) is removed or the cable is cut the resulting open circuit will make the voltage from the CO go to maximum looking to make that 10Ma current flow.

-Hal

 

[EV607797]

Let's not forget about OPX circuits (OL13A, B or C). In order for some long loops to be accommodated, the tip/ring voltage can (must) be jacked up significantly. We currently have a customer located about eight copper miles from the CO and the telco had to increase the voltage to -96 volts DC to compensate for voltage drop.

 

[dereckbc]

Let's not forget about OPX circuits (OL13A, B or C). In order for some long loops to be accommodated, the tip/ring voltage can (must) be jacked up significantly. We currently have a customer located about eight copper miles from the CO and the telco had to increase the voltage to -96 volts DC to compensate for voltage drop.

Must be a rural Telco who are too poor to afford a SLC :grin:

 

[don_resqcapt19]

Dereck,
The cable tech said it was a plus and minus 130 volt supply giving an open circuit voltage of 260.
If the voltage is 130, that would trigger the OSHA rules for 1000 volt rated gloves...I can't imagine working on 22 gauge conductors with 1000 volt gloves on! This cable does have at least 2 DS-1 (T-10) pairs. One for the phone system and one for the data connection. The conduit that i was installing was so that the phone company can extend a fiber connection into the customer.
Don
It should read (T-1) in the 3rd line.

 

[EV607797]

Must be a rural Telco who are too poor to afford a SLC :grin:

Actually, no it's in a major metropolitan area. Verizon just saw these as short-term installations while a customer was waiting for an office expansion build out. They couldn't justify the expense of a SLC or equivalent for only a six-month application.

Ironically, the two sites are only across the street from each other, but the CO is four miles away from each site. They just used Lorraine units in the CO to boost the voltage and cover the loop length. Of course, this also means that the message waiting lamps on the remote phones stay lit continuously.

OPX circuits are fairly rare any more, so I guess they just took the path of least resistance (no pun intended).

 

[dereckbc]

Don,
I have never heard of or seen any 260 volt systems in my career. Not saying they do not exist, just never heard of it. Doesn?t really matter the principle of a Loop Carrier is still the same regardless of voltage, as they are current supplies up to a voltage limit to overcome long loop resistance.

My only comment is I cannot imagine extremely long copper circuits in the Chicago Metro-Plex area without a CO within a few miles or using fiber for the long range stuff. 130 VDC is good out to about 10 to 15 miles depending on wire gauge.

 

[don_resqcapt19]

Dereck,
I am a bit more out in the "sticks" about 90 miles southwest of Chicago. The customer is about 5 miles out of town and about 8 miles or so from the CO. It is also on a cable that has a history of "water" problems for sometime.

130 VDC is good out to about 10 to 15 miles depending on wire gauge

The one I cut was 22 gauge, not sure if it is the same all the way back to the CO.
Don

 

[cnavarro]

High voltage...just in passing

High voltage...just in passing

Back in the day, I imported dial tone from my toll center to two of my tribs. The distance via the two Central Offices was about 25 cable miles A pair of Lorain loop extenders (one at each office) solved the problem of signalling.
After I transferred out of the tribs, they said it was like the 4th of July when they cut out the loop extenders wired back to back

Our first interconnect multiplexer used 260 volts on a single pair to derive 5 phone lines a distance of 1.1 miles. Since our pair was an OPS, we told the telco to safeguard the pair and they did, as most installers would not expect the additional voltage.

The second one, a real telco grade multiplexer, used something more reserved like 200 volts.

Carl

 

[VernB]

As a rule, +-130VDC was only found on analog carrier circuits (which would be VERY rare to find anymore), old style payphone circuits (only when operating, +130 signals the phone to collect the coins, -130 signals the phone to refund the coins), or legacy repeatered long run T1 circuits. The +-130VDC on analog carrier circuits and repeatered T1 spans is fused at only .180A so it doesn't require 1000V gloves to handle :roll: (Class A3 voltage).

Modern T1 over HDSL/HDSL2/HDSL4 uses approximately 180VDC for span powering, however, the 180VDC is limited to 1mA and not present until both ends of the circuit are connected (Class A2 span powering voltage).

If anyone really cares, the standard for this is Bellcore standard GR-1089-CORE. Rubber gloves aren't required until Class AB voltage (up to 90VDC or 90VAC, up to 15A, up to 1350VA).

Vern

 

[ryan_618]

You mean you didn't have an arc blast suit on while you were digging?