Hello,
I fitted an extension socket and was reading which colour cable to connect where. I was using wires with two pairs: blue/white and orange/white pairs. I read that rarely a third pair (green/white) is connected to terminals one and six. What were these used for and why are they no longer used? I am guessing they were used for something once upon a time otherwise they would not be there.
Thanks, Stephen.
In article , Stephen scribeth thus
might help...
Used for lights and buttons on special phones on office phone systems.
Owain
I'm afraid it doesn't. I had already found that site by google. There's a lot of information there but all it says about the green/white pair is:
"Terminal pins 1 and 6 may be absent on some versions of C/NTE5, but these connections are not normally used anyway."
I notice all web sites say something similar "not normally used" but they don't say "never used". This implies that occasionally they are used but what for? And why do manufacturers spend money including them if they don't have a use?
If I add any more extensions is it worth using 3-pair/6-core cable or can I save some money by buying the 2-par cable?
Thanks.
2-pair is fine for normal extension sockets. As almost all phones now synthesize the bell signal internally the terminal 3 wire isn't needed either! You can just use a single pair.
The only time that you need additional cores are when you have some types of PABX on your system. Details for connecting these will come with the PABX - there isn't a standard AFAIK. Wire 3 is the "Bell" wire and is used to stop other phones "tinkling" as a dial phone dials a number. It's just about always redundant now (even though it's officially still part of the spec).
Manufacturers have to make their connectors suitable for all the systems that are out there - and they are standard connectors now. That's why all the terminals are provided.
Don't be tempted to mix ethernet pairs with telecom pairs in the same cable. You'll probably find that it's part-functional, and very annoying to debug! It's just not worth it for the cost saved.
They're actually used in my house!
My master socket used to be right alongside where the overhead cable entered in the living room.
When I went isdn before ADSL, BT moved the master socket to the study adjacent to the pc, and installed a secondary socket where the master used to be, with a three pair between them. The green and white take the incomer to the master on the three pair.
I believe that terminals 1 & 6 were for Telex.
See Table 1 of SIN 331, "BT 50 Baud Telex Service, Interface Description & Withdrawal Notification",
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