[Asterisk-Users] Do I need a ring capacitor to use TDM400P cards in UK

[Mark Elkins]

On Wed, 2005-06-08 at 23:39 +0100, David John Walsh wrote:
> Angus

Jumping in with both feet....

> a "BT" socket with a capacitor in is commonly refered to as a "Master
> socket", and are very cheap even without wholesale.  It gets its name
> from being the socket that BT installed into the house for the line,
> all other sockets in the house will be slave or secondary (ie no
> capacitor) (and its against the law to play with the one BT installed
> - but thats off topic!)

..and it complicated my understanding of how to get ADSL working at the
same time.... so ADSL filter was installed before the Master...


UK Phones at homes historically had a separate bell - mounted in the
hallway. Phones where then placed where convenient. This allowed one
loud bell (sucking current) and multiple (quieter, less current thirsty)
phones...

To do this, the 2-wire line from the Telco was altered into a three wire
line inside the residence, the job of the 'Master Jack'. This is done
with a capacitor from one of the legs to provide the third wire. Look
inside the 'Master' to confirm... (there might also be a resistor from
the other leg to the new third leg too).

(I can remember playing with a crystal radio set, that needed an earth,
and the instructions saying to use the metal (silver coloured) finger
stop on the rotary dial as an earth - so there may be an earth as a
fourth wire...)

Because of this - many phones sold in the UK will only ring via this
third wire...

I vaguely remember bringing a cordless phone from the UK to South Africa
(where the US 2-wire equipment work fine) and adding a capacitor inside
the phone to make it Ring... 

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