The newer demarks have lightning protection and a loop back to isolate the customer equipment from the line. I have a 6 line unit with this feature. It depends on when the equipment was installed as to which type of protection is at the customer premis. The loop back is used in conjunction with the MLT computer systems to perform loop resistance tests, ground tests and customer equipment resistance tests. This is done daily in offices so equipped. In a lot of cases I equipped them. Vern Bob Ammerman wrote: > > So, if I understand you correctly: > > For residential installations the telco generally have one pair hard copper > directly from the CO to the home. They have a loopback/isolator at the CO, > and a lightning arrester at the demarc. And that is all. > > No wonder I never saw one. > > Bob Ammerman > RAm Systems > > ----- Original Message ----- > From: "Larry Taylor" > To: > Sent: Monday, September 22, 2003 10:16 PM > Subject: Re: [PIC:] Stealing power from the phone line update > > > BOB! The loopback is in the treatment card that interfaces with the phone > > line to the customer equipment not in the Demarc. The Demarc is after > there > > equipment. That is normally power locally but can be powered from the > Phone > > Company. If this is at a home that little thing that the phone company > wires > > to is just a Lightning protector that goes to ground when there is a > strike > > that can be close to the phone lines. Treatment cards are used for looping > a > > 4 wire line. Tx on one pair and Rx on the other pair. This is used on Data > > lines,Phone Trunks, not on a regular phone lines. Ring voltage 90 vac > 20hz, > > 48vdc minus line lost to phones. Phones look like 600 to 900 ohms.when its > > off hook. They trigger the loop back with a tone 2817hz. > > Larry Taylor KF6JBG Telecomm > > ----- Original Message ----- > > From: "Bob Ammerman" > > To: > > Sent: Monday, September 22, 2003 3:01 PM > > Subject: Re: [PIC:] Stealing power from the phone line update > > > > > > Hm... > > > > Never saw one around here, but it sure makes sense. > > > > I do have a demarc box a buddy just gave me. It is pretty recent. I'll > have > > to look inside. > > > > Any idea how they trigger it? > > > > Bob > > > > ----- Original Message ----- > > From: "Vern Jones" > > To: > > Sent: Monday, September 22, 2003 3:44 PM > > Subject: Re: [PIC:] Stealing power from the phone line update > > > > > > > This isolation relay, or loop back relay is in the Telco Demark box in > > > recent installations. This is used to let them know whether the trouble > > > is yours or theirs. > > > > > > If your service hasn't been upgraded for 30 years, then you won't have > > > one. > > > > > > Vern > > > > > > Bob Ammerman wrote: > > > > > > > > > In the states with Telephone offices equipped with MLT (most with > > > > > electronic switches and former Bell companies), lines are normally > > > > > tested 1 time each day, testing for line faults. If current is being > > > > > drawn, it looks like a bad pair to MLT. > > > > > > > > > > They may look more closely using the isolation relay to determine > > > > > whether it is the pair or your equipment. This could possibly > generate > > a > > > > > letter to you requesting that you fix your equipment, or disconnect > > it. > > > > > > > > > > Vern > > > > > > > > Where is this 'isolation relay'? I have never before heard about that. > > > > > > > > Bob Ammerman > > > > RAm Systems > > > > > > > > -- > > > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > -- > > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu