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: Dial pulse distortion caused by loop leakage
Keywords: SK2086, phones
Message-ID: <5000@kitty.UUCP>
Date: 3 Jun 91 04:29:00 GMT
References: <1084@eplunix.UUCP> <1991May29.084859.5324@specialix.co.uk> <8085@nst>
Followup-To: sci.electronics
Organization: Recognition Research Corp., Clarence, NY
Lines: 19

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.

	There could well be a problem if rotary dial pulsing is used.
Such current leakage of 7 mA or less can well result in dial pulse
distortion, especially if pulsing an "A-relay" on a longer loop in an
electromechanical central office.  Loop leakage effects are much more
evident due to residual magnetism in a relay, as opposed to rotary dial
pulsing with electronic loop current detection.

	This is not, of course, a problem when DTMF signaling is used.

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