Master socket for PABX?

[boombox]

Just wondering why the advice is to fit master sockets for PABX such as the BT/Lake range of PABX? I'm sure I've just used slave sockets in the past and they've worked fine?

Thanks

[Dave Moll]

They'll be fine as long as the telephone equipment plugged into them doesn't require the separate ringing wire. Anything that does won't ring, but should probably otherwise work OK.

[boombox]

Originally Posted by Dave Moll

They'll be fine as long as the telephone equipment plugged into them doesn't require the separate ringing wire. Anything that does won't ring, but should probably otherwise work OK.

Ah OK. The phones connected to this particular PBX are modern, imitation GPO telephones. Guess that's why they work! Thank you!

[julie_m]

There used to be such a thing as a "PABX Master" socket, which included the ringing capacitor and sometimes the resistor but no surge protector.

If you were wiring up a big enough site, you might make a saving using them .....

[TonyDuell]

Last time I looked in Maplin they sold 3 types of telephone adapter for 'structured wiring' systems -- that is with a 8p8c plug on the input side, middle 2 contacts used for the telephone line.

'Extension' which had no internal components (I forget where the bell shunt (ringing) wire appeared on the 8p8c plug).

'PABX Master' which contained the ringing capacitor and out-of-service resistor but no surge protector'

'PSTN Master' which also contained the surge protector (same circuit as a normal BT master socket).

I use a couple of the last type with my telephone line simulator. I am sure the PABX master ones would have been fine too, but I think Maplin didn't have them in stock when I went to buy them

-tony

[julie_m]

The ringing wire is not present in the 8p8c (RJ45) connector. Pins 1, 2, 3 and 6 are Internet; pins 4 and 5 are analogue telephone; and pins 7 and 8 are spare, or a second analogue phone line. The capacitor, if present, is wired between pins 2 and 3 of the RJ431 socket.

It was an interesting idea; but then along came 1GB ethernet, which uses all four pairs, and Mark Spencer pretty much killed off analogue phones anyway

[boombox]

Originally Posted by julie_m

Mark Spencer pretty much killed off analogue phones anyway

who?

[julie_m]

Mark Spencer -- the original lead developer of Asterisk. Also responsible for GAIM, which eventually became Pidgin.

[TonyDuell]

Those Maplin adapters (at least the ones I have) bring out the telephone earth (pin 4 of the BT socket) on pin 8 of the 8p8c. I never looked at the extension one in any detail, but it's possible the Bell Shunt wire came out on pin 7.