Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!ub!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Drawing DC phone current
Summary: Automatic line insulation testing
Keywords: SK2086, phones
Message-ID: <5001@kitty.UUCP>
Date: 3 Jun 91 04:40:20 GMT
References: <1991May29.084859.5324@specialix.co.uk> <8085@nst> <107170@sgi.sgi.com>
Followup-To: sci.electronics
Organization: Recognition Research Corp., Clarence, NY
Lines: 27

In article <107170@sgi.sgi.com> rpw3@sgi.com (Rob Warnock) writes:
>|  Telephone line circuit switch hook detectors are designed to operate
>| at currents ABOVE 12mA. They are also designed NOT TO operate at
>| currents LESS than 7mA. 
>| 
>| No problem will result if you draw less than the 7mA from the loop.
>
>No *immediate* operational problem... However, in the nightly automatic test
>scans [forgot the Telco acronym], your line will be flagged as "leaky", and
>may eventually spit out a trouble ticket. When they figure out the "leak" is
>inside your house, they'll send you the "repair bill" for a "false service
>call due to customer premises equipment".

	In general, automatic line insulation test apparatus (ALIT) is
concerned with leaks to ground or presence of foreign EMF from another pair.  
Such conditions are indicative of cable faults.  The primary purpose of
ALIT is as an early warning of outside plant cable trouble - and not as
an indicator of subscriber instrument trouble.

	While it is possible to configure more intelligent ALIT apparatus
to perform a tip-to-ring resistance test, this is generally not done due
to the possibilty of false alarms.  Such false alarms are most commonly
caused by old, leaky series ringer capacitors.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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