[Asterisk-Users] FXO vs FXS question

[Andres Tello Abrego]

I have blown one fxs module in that way :(

It´s a warning, and you MUST be careful of tring no to do so.

Steve Underwood wrote:
> Andres Tello Abrego wrote:
> 
>> The way I explain the difference between fxo and fxs, is electrically...
>>
>> The telco lines, PROVIDES voltage and current to makes the telephone 
>> ring, so the FXO is a device, adapted to recive this voltage an current.
>>
>> The phone, NEEDS voltage and current, to ring, so the FXS is a device, 
>> adapted to provide this voltage and current.
>>
>> So, if you plug an FXS to a Telco Line, both equiments PROVIDE voltage 
>> and current, so... what you have? Sparks and a short cut, and at least 
>> like 75usd of the fxs module or even worst, like 100usd for iaxy or 
>> fxs card :(
> 
> 
> When I designed line cards for the PSTN we specifically tested that this 
> sort of thing would not happen. Phone lines are handled in a pretty 
> sloppy way. If a line card in an exchange blew up every time someone 
> shorted two lines together they would be replacing cards all day.
> 
> Regards,
> Steve
> 
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