sundance-communications.com/forum Forums General General Telephone & Systems Information loop current

found this at https://www.mailarchive.ca/lists/comp.dcom.telecom.tech//2001-02/0291.html


At 20 mA or greater, it is offhook. At 18 mA or lower, it is onhook.

The switch should supply a minimum of 23 mA.

The absolute maximum allowed is 120 mA. The max recommended is 60 mA.

Typical values range from 23 mA to 55 mA, with 28 mA to 45 mA being the most common.

Perhaps the most notable thing about the above is that any resistance in series with a loop should be capable of dissipating the heat generated when 120 mA of current flows (and the assumption should be made that enough voltage can exist to cause that much current). That can be a significant amount of heat!

Thanks all,
Guess it's time to stock up on current regulators. Hate losing the fight, when I know I'm right, just can't prove it. Think I'm going to give this to the PUC. If I can't get them to correct the problem at least I can give them some grief.
Bill

Your rage is focused in the wrong direction. The manufacturers should be taking line conditions into consideration when designing systems.

Well Perry, I agree the manufactures should make there equipment met the ANSI standard, but the manufactures shouldn't have to make something that will work no matter what you throw at it, that's why the standards are there. I ran into this type of stuff a lot when working on special circuits. The circuits weren't up to standards, not AT&T standards, but the Bell standards. That's why they are there to protect the public and that is why the ANSI standard was developed, I only ask they live up to them. Since no one seems to know of any changes they are out of limits on their own standard. Not rage just trying to get someone to live up to their end of the bargain. And yes, I will put limiters on to fix the problem, but I won't give up trying to get the LEC to fix theirs.
Bill

I know this is an old post, I dug it up on purpose so as not to rehash this subject. Since I had some time and since I'm having problems related to what I believe is high loop current I did some digging. These are the specs companies list to meet loop current requirement, you can't get these specs without paying for them. Bellcore LSSGR Sec 6, TR-NWT-000506, EIA RS464A. Now here is the surprising part. The companies say these specs quote loop current as between 20ma and 120ma. I spoke to Mike Sandman and says he knows it's above 100 on the high end. So since many manufactures are using the old standard of 20-40ma you can have problems. I currently have a problem on a fax detect circuit on a Vodavi STSE, which I hope I've corrected with loop current regulators. Also I've had several people tell my there fax detect, fax machine or modems just don't seem to last long, which I think is also due to high loop current. This is just FYI for those that need it. I think this will be a problem more in the rural areas than in the cities. I am going to see if Qwest can provide me with any of the documents.

The telco here had a probem where they had a fiber coming into a remote in the bottom of this building and they were using Nortel single line sets and the message lite would come on and the message indicator came on by itself. The fix for them was to put a jack with a small cord on it and put resistors in series with each side of the line. Plug this into the wall jack and the set this jack with the resistors and everything was fine. Ordinary sets worked ok with out it.

form what I have been told 20ma to 120 ma is acceptable as per bell core spec but the preferred operating range is 20ma to 80ma, the closer to 20ma the better.
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other specs:
TYPICAL operating limits
talk battery -48VDC 47-->-105VDC
loop resist. 0-1300 ohms 0->3600ohms
loop loss 8 DB 17 DB
Distortion 150db N.A
RING SIGNAL 20hz @90vrms 16-->60HZ,40--130v
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The problem is the equipment manufactures are using the 70's standard of 20-40ma. At least that's what the manufacture I asked quoted me. As you know it used to be the trouble was low loop current, only in the last few years has high loop current become a problem. Thanks for the added info.

FYI the Qwest supervisor just called and he said the EIA standard is 23-70ma..still waiting for document in hand.

Justbill - from my experience (for what thats worth) is that when the loop current gets up above 34-35ma that some funky trouble will crop up. I recently had a customer that could not receive fax transmissions from customers in Texas, California and New York. Other LD customers were OK. The interesting thing is that this customer did not have any problems at their old location, but when they moved to the current location the fax problems started. That within itself made me think it was something related to the C.O. at the new location. I measured the loop current and it was 37ma. I added a current regulator and, viola, the problems disappeared!
I have also had problems where the line would squeal when a conference call was established with two trunks - again, current regulators solved the problem.

I believe that modern electronics are far more sensitive than equipment manufactured when >40ma was acceptable.

Bill

I agree 100% As Sandman said, we know this, but your not going to convince the LEC's or the equipment manufactures. That's why he sells loop current regulators. Hmmmmm$$$$$ how do ya make those things. :rolleyes: