Path: utzoo!utgpu!cunews!software.mitel.com!grayt
From: grayt@Software.Mitel.COM (Tom Gray)
Newsgroups: sci.electronics
Subject: Re: Drawing DC phone current
Keywords: SK2086, phones
Message-ID: <8129@nst>
Date: 3 Jun 91 16:40:20 GMT
References: <8085@nst> <107170@sgi.sgi.com> <1991May31.135017.13702@specialix.co.uk>
Organization: Mitel. Kanata (Ontario). Canada.
Lines: 31

In article <1991May31.135017.13702@specialix.co.uk> stevem@specialix.co.uk (Steven Murray) writes:
:rpw3@rigden.wpd.sgi.com (Rob Warnock) writes:
:
:>In article <8085@nst> grayt@Software.Mitel.COM (Tom Gray) 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".
:

The periodic tests on the subscriber loop will not normally look for faults 
between tip and ring.

Also to render a little bit of reality back into this discussion, there 
is automatic equipment designed to operate at the end of telephone loops.
In the days before microprocessors and integrated op amps (when dinosaurs
ruled the world and I travelled daily past the brontosaurus store), these
detectors consisted of high resistance relays. If your tip to ring
resistance is greater than 10koms nobody is going to get excited
(ie 4mA). If your tip to ring resistance is greater than 30kohms,
nobody will ever know.