Solved

Telephony: Minimum Loop Current on an Internal Telephone Line (FCC Specifications)

Posted on 2006-10-29
3
568 Views
Last Modified: 2007-12-19
Does anyone know if there are any FCC regulations specifying the minimum loop current on a telephone line. I am referring to the off hook current the is supplied to the telephone/fax by the carrier down the telephone lines. FCC part 68 specifies that the loop current should not exceed 100mA and there is reference to a minimum of 20mA, but I am not sure about this.
0
Comment
Question by:Vespa72
  • 2
3 Comments
 
LVL 20

Accepted Solution

by:
Lazarus earned 500 total points
ID: 17831487
Currently there are no FCC rules as to Loop current.

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!

There is an ANSI standard though:
I cannot give a real answer to your problem since I have not seen the specifications. However, the ANSI/ISA S50.1-1972 standard specifies the use of 4-20 mA current loop to communicate the value of a process variable corresponding to a 0-100 percent full scale value. This is analog data transmission.

Another specification used in data communications is known as the Bell 202 (Bellcore) standard that calls for a constant current, usually 20 mA, to be carried on a two- or four-wire circuit. The data is communicated by use of FSK, Frequency Shift Keying, where one frequency, 1200 Hz represents a mark or 1, and another 2200 Hz represents a space or 0.


This little write up on Loop Curent might be of help to you though.
http://www.sandman.com/loopcur.html
0
 
LVL 1

Author Comment

by:Vespa72
ID: 17831533
That confirms my suspicion of the problem I am having. The clincher for me will be to try and hold my carrier to supplying greater than the 20mA they are currently giving. Thanks!
0
 
LVL 20

Expert Comment

by:Lazarus
ID: 17831559
Good luck with that. It's to the telco intrest to keep them as low as possible. But it should be at around 23ma.
0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
perfect consistent volume 6 61
How to write an English digest paper 6 76
Problem to file 4 28
how many cores in note3? 5 49
Originally published Entrepreneur.com Booming numbers of freelancing professionals are changing the face of work. In the United States alone last year, the number of workers freelancing grew from 700,000 to 54 million, according to a Freelancers’…
With the shift in today’s hiring climate (http://blog.experts-exchange.com/ee-blog/5-tips-on-succeeding-in-the-new-gig-economy/?cid=Blog_031816), many companies are choosing to hire freelancers to get projects completed efficiently and inexpensively…
The Bounty Board allows you to request an article or video on any technical topic, or fulfill a bounty request to earn points. Watch this video to learn how to use the Bounty Board to get the content you want, earn points, and browse submitted bount…
Notifications on Experts Exchange help you keep track of your activity and updates in one place. Watch this video to learn how to use them on the site to quickly access the content that matters to you.

820 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question