Path: utzoo!telecom-request Date: Fri, 7 Jun 91 18:25 GMT From: Proctor & Associates <0003991080@mcimail.com> Newsgroups: comp.dcom.telecom Subject: Re: Busying Out a Phone With a Resistor? Message-ID: Organization: TELECOM Digest Sender: Telecom@eecs.nwu.edu 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 434, Message 6 of 9 Lines: 31 In issue 425, Marc Unangst writes: > I recently had one modem in the middle of a 15-line hunt group go out. > Not wanting to move the rest of the modems up a line each, I did some > investigation with a VOM and a telephone, and discovered that plugging > a 270 ohm resistor into the phone line (across tip and ring) should > have almost the exact same effect as an off-hook telephone does -- > thus busying out the line. Now, my question is, is there anything > wrong with doing something like this? Will a 1/2W resistor be enough? A half watt resistor is not enough. The worst case would be if you were next door to an old C.O. running fixed battery feed of 52 vdc and A-relay resistance of about 400 ohms. This would give you about 78 ma of loop current and the resistor would have to dissipate around 1.6 watts. So that the resistor wont heat up too bad, it is best to spec the resistor wattage around twice that, so figure a three watt resistor. As long as you can draw at least 20 ma of loop current, the C.O. should detect an off hook condition. A safe bet is to use a 400 ohm resistor, which will give you a lower current draw. But the higher the resistance, the more power must be dissipated by the resistor for a GIVEN amount of current. If the C.O. battery was 48 volts and total loop resistance was about 700 ohms, the power load on the 400 ohm resistor (this all is emitted as heat) would be about 3/4 watt. Paul Cook Proctor & Associates Redmond, WA 206-881-7000 3991080@mcimail.com