[Asterisk-Users] Loop length supported by FXS module on Wildcat TDM400 card

[Brian Cuthie]

Steven Critchfield wrote:

>On Fri, 2004-05-14 at 16:12, Elliot Eichen wrote:
>  
>
>>Does anyone know (appoximately) the max loop length that the FXS module on a
>>Wildcat TDM400 card will drive an analog phone(over standard - say cat3 or
>>26 gage twisted-pair wire).  It's clearly not going to be 18kft, but perhaps
>>4000 feet?
>>    
>>
>
>I'd be wary of 4kft even if it could do it. Thats a long way for
>something to short/introduce power and fry your complete computer.  It
>would be pretty easy to put a cheap pc local and run a few feet of
>cable. This is especially true if you run more than one line. 
>  
>
Shorts won't be a problem since any reasonably designed FXS interface 
has current limiting. In fact, it's this current limiting and the 
relatively low loop voltage (I'm guessing 24V on a card of this type) 
that will restrict usable loop length. As you point out, induced 
transients are also a problem. So if you have a long loop make sure you 
put telco surge arrestors on each end.