Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!rpi!bu.edu!telecom-request From: kabra437@athenanet.com (Ken Abrams) Newsgroups: comp.dcom.telecom Subject: Re: How to Hook up a Phone For a Play Message-ID: Date: 25 Feb 91 21:30:39 GMT Sender: news@bu.edu.bu.edu Organization: TELECOM Digest Lines: 29 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 164, Message 12 of 13 In article floyd@ims.alaska.edu (Floyd Davidson) writes: > In reference to using 117 VAC 60 Hz to ring a phone: > One more time: 100 VAC 20 Hz is JUST as dangerous, if not more so, > that 117 VAC 60 Hz. Using house current to ring the phone is no more, > and no less, dangerous, than ANY other reasonable way you can make the > ringer work. The REAL issue is not the voltage applied but the ability of the source to provide current limiting. 10,000 volts at .00000001 ma is not dangerous (static electricity). 100V, 20HZ and 117V, 60 HZ are both deadly if they are not current limited. The wall socket that provides the 117V certainly is NOT current limited (to any practical degree) without a device in series to accomplish that. A suitable current limiting device would make 117V, 60 HZ suitable for use to ring the phone with little danger. The 88-100V, 20 HZ normally used to ring a phone on the network is current limited at the source AND by virtue of the loop resistance between the CO and the phone (typically 200 to 500 ohms or greater). Standard telco ring voltage will give you a nasty surprise but is not (usually) dangerous because it IS current limited. Ken Abrams uunet!pallas!kabra437 Illinois Bell kabra437@athenanet.com Springfield (voice) 217-753-7965