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: <8085@nst>
Date: 29 May 91 18:52:45 GMT
References: <8053@nst> <1084@eplunix.UUCP> <1991May29.084859.5324@specialix.co.uk>
Organization: Mitel. Kanata (Ontario). Canada.
Lines: 33

In article <1991May29.084859.5324@specialix.co.uk> stevem@specialix.co.uk (Steven Murray) writes:
>raoul@eplunix.UUCP (Nico Garcia) writes:
>
>>In article <8053@nst>, grayt@Software.Mitel.COM (Tom Gray) writes:
>>> Draw less than 4mA from the loop and you will not have any 
>>> problems.
>
>>Only works in the off-hook position, Tom. A standard phone is about 600
>>ohms, and has about 10 Volts across it off-hook. That's *about* 15-20 mA:
>>the standards are deliberately extremely broad. It's not clear at all to me
>>that 4 mA will not maintain the "off-hook" status in the phone company's
>>circuits. However, the phone company does *not* want DC paths available for
>>the on-hook state. 
>

 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.







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Tom Gray



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