Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!swrinde!ucsd!casbah.acns.nwu.edu!nucsrl!telecom-request From: jon_sree@world.std.com (Jon Sreekanth) Newsgroups: comp.dcom.telecom Subject: Re: Should Projects be Connected to the Phone Line? Message-ID: Date: 15 Feb 91 17:37:55 GMT Sender: news@casbah.acns.nwu.edu Organization: The World Lines: 54 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 118, Message 7 of 12 In article <74667@bu.edu.bu.edu> atn@cory.berkeley.edu (Alan Nishioka) writes: > Is this safe? Are there other concerns here that I am missing? The thrust of FCC 68 is that you don't damage or overload the telephone network. Hence the load limitations : maximum of 1.6K AC to ring current, max of 5 Meg DC on-hook. Another concern is signal power injected back to tip and ring. If your device does not intend to send back audio signals, then there are (generous) limits on out of band signal power, such as leakage from high frequency clocks in your digital section. The isolation requirements call for up to 1500V of insulation between tip/ring and any user accessible, outside parts of your box. FCC 68 also specifies that after a simulated lightning strike, 800V spike, 10uS rise, 560uS fall, 25 amp max surge, your equipment should still meet the impedance and signal power limitations. If you use an MOV on tip and ring, that should cover it. A relatively new requirement, UL 1459, is required from July, 1991 onwards (for phones, I'm told). The big deal about this test is your circuit must not burst into flames upon application of 600V RMS across tip and ring for 30 minutes or more. (The test is sneaky: if you use a series fuse, they're allowed to current limit just below the fuse limit, and see if the rest of your circuit burns) All this sounds a little overwhelming, I know, but the reason it's so fresh in my memory is because we're going through the process ourselves. I covered the main points above, but there might be some more that I missed. > Should *anyone* build *anything* that connects to the phone line? Can > it be reasonably priced? Does the phone company really care? Should > I do it anyway and just kinda feel guilty? :-) From personal experience, if an experimental circuit is briefly connected across a line, the telephone company does not notice it. But I'd not leave such a circuit connected while I'm not around to observe it. My judgement is : the few dollars saved by leaving a hacked up circuit connected to the line are not worth the potential risk of the insurance company refusing to pay for a fire or personal injury that the device caused (to take an extreme example). Regards, Jon Sreekanth Assabet Valley Microsystems Fax and PC products 346 Lincoln St #722, Marlboro, MA 01752 508-562-0722 jon_sree@world.std.com