Line Cord Colour Coding

[BakeliteBear]

I have converted many telephones over the years and I think it’s about time I understood what I was doing!! I would like to start with my colour coding mystery.

My question originates from the wiring of 232’s. The original wiring uses white, green and red, whilst the accepted conversion substitutes the current blue for the green and reverses the white and red. So what’s going on here?

Thanks Chris

[AndiiT]

Hi,
Whilst not 100% sure on this I think that some earlier telephones had the ringing capcitor in the 'A' leg of the Bell circuit and not the 'B' leg, as is current practice.
This would explain your need to reverse the Red and White tails of the line cord when doing a conversion otherwise the bell would not ring in your modified telephone(s) due to the ringing current being presented across the point where the original capacitor was strapped and not the bell coils.


I have just had a look at the N digram of a 232 and found that it has no internal bell or capacitor, the reason for the reversal in this case is so that the "Anti - Tinkle" (Blue wire) operates correctly when other telephones are conected to the line

Regards
Andrew

[BakeliteBear]

Thanks Andrew,

I do also know that if the red and white are not reversed, the reception in 232’s is very very quiet. I have never understood why this should be the case.

[AndiiT]

Hi,
The 232 telephone was orignally designed to be used in conjunction with a seperate Bellset, which contains its own Capacitor, if you do not reverse the red and white connections to the 232 when converting the voice component of the transmission will be shunted by the capacitor in the master socket/NTP reducing the reception volume.

Andrew

[BakeliteBear]

Thanks for all that Andrew.

Last question on this one - I understand the blue is for anti-tinkle, but why was it green in the original diagram? Were the colour codes changed or was it that the green had a different function?

[Dave Moll]

Don't forget that the original arrrangement with multiple instruments was to wire the bells in series. I understand that the green wire was used between two series bells.

I assume that this arrangement was limited to two units - but it was rare enough to have even two extensions, so presumably more than that was pretty well unheard-of.

[AndiiT]

Hi,
I am unsure of why the change was made.

In the orginal "newer" 700 series telephones, when hard wired, Blue was used for earth recall or C-wire signalling (on a PBX) or earth calling, as in the case of a party (or shared service) line.
Green being the series return wire for the bell circuit - a strap was fitted in the block terminal to allow an extention bell to be wired in place of the strap.

Green became the PBX earth wire when converted to Plug and socket, perhaps this was simply related to the fact that the green wire was connected to terminal 4 at the socket end or maybe the GPO/BT just felt like a change.

Andrew

[russell_w_b]

Originally Posted by Dave Moll

I assume that this arrangement was limited to two units - but it was rare enough to have even two extensions, so presumably more than that was pretty well unheard-of.

One was allowed six extensions with series bells, as I recall.

[BakeliteBear]

As ever I a very grateful for all your help – thank you.

So would it be correct to say the current domestic colour only relates to ‘Plug and Socket’ and before that cable colour were given different functions?

Having never been a telecoms engineer, plan 1A, 1B, 1C, 2, 2A, 105, 107 etc means nothing to me. I am just tring to make sense of it as an ‘outsider’ and what might be perfectly obvious to the forums many expets seems very much like a ‘dark art’ to me!!

[AndiiT]

Originally Posted by BakeliteBear

...So would it be correct to say the current domestic colour only relates to ‘Plug and Socket’ and before that cable colour were given different functions?...

That would be correct

Originally Posted by BakeliteBear

plan 1A, 1B, 1C, 2, 2A, 105, 107 etc means nothing to me.

The GPO used a number of different 'Plan' systems to cope with various customer (or should that be subscriber?) requirements, the most common of these being Plan 1A which, at its most basic was one Main and one Extention telephone but allowed a maximum of six telephones to be fitted (I believe this was limited to Three in the case of a shared service, or party, line) to one exchange line.

Another common installation was Plan 4 where the telephone(s) were made portable by the use of a Jack plug and Socket arrangement and the use of a fixed Bell to alert an incoming call in the event of the Telephone not being plugged in (no opt out of service option as with the "New" Plug and socket system)

More details about various Plan systems can be found Here

Regards
Andrew

[Station X]

Plan 1A was the most common and the phones, apart from one, were fitted with a switch to short-circuit the bell in the phone. I think that Plan1B didn't have the switches.