Telephone wiring

[ban-all-sheds]

Small enough for there not to be catastrophic voltage drop.

 

[JohnW2]

I don't think anyone (certainly not me) has said anything about 'catastrophic' voltage drops. I merely commented that, certainly in the days of electro-magnetic bells etc., the VD was likely to be of a magnitude that renders an argument as to whether the supply voltage is/was 48V or 50V pretty unimportant, probably to the extent, as had been said, of being pretty pedantic. As has been said, in context (i.e. 'on topic'), all that matters to the OP (as an indicator of whether the line is 'live') is whether there is any 'significant' voltage measurable between the BT conductors, regardless of the magnitude of that voltage.

Kind Regards, John

 

[sparkymarka]

Cable lines are in 35 ish volts dc ....so it ain't going to cause any issues with the handset ....due to voltage drop ! So are some pabx ...

 

[SUNRAY]

I'm certainly not being pedantic here, just chewing the cud. I left BT in 1994 and realistically I have absolutely no idea what has happened since then. As a freelancer I've had a little experience within telecoms but if I'm honest more in terms of wiring or possibly labouring than any serious technical capacity.
Out of curiosity I checked my phone line today and found 50.67V and 38.55V off hook.
I believe I recall acceptable line currents of 30 to 100mA and found a s/cct of 107mA and my BT Dect phone 69mA at dial tone part of call, so all very memorable figures.
I have done a little work for one of the cable providers and the biggest problem there seemed to be customers unsuccessfully trying to use older phones on the lower networks voltage.

 

[AndyPRK]

What decade do you call older ?

 

[ban-all-sheds]

Young Mayn!!!

 

[SUNRAY]

What decade do you call older ?

40's/50's/70's/80's
I found the 700's are OK but the subsequent electronic kit is hit and miss. Later versions seem fine.

 

[Taylortwocities]

40's/50's/70's/80's
.

Oi! What about the best decade ever?
Summer of love, flowers in your hair, pirate radio, frozen jubblies…

 

[SUNRAY]

Oi! What about the best decade ever?
Summer of love, flowers in your hair, pirate radio, frozen jubblies…

Hey Mmmaaaan, suuurrre best decade ever.
Such a good decade that even the 7oo type tele's of the era are laid back enough work on lower line voltage.

 

[Taylortwocities]

Cool

OK, back to @russ8585

Where have you go to on this? Any progress?

 

[bernardgreen]

Old phones work quite happily ( speech ) with 9 volts on the A B pair.

 

[securespark]

40's/50's/70's/80's
I found the 700's are OK....

Wow! You were around in the 700's??

 

[securespark]

recall

Bit of a telephone injoke there...

 

[bernardgreen]

No telephone ( operator ) jokes please.........

 

[ban-all-sheds]

frozen jubblies…

Poor girls.