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#140015 01/09/04 01:44 PM
Joined: Jun 2002
Posts: 159
Would any one know the ringing voltage on a standard BT line.
Some may argue that a BT socket should not be fitted in a UK bathroom.


lyle dunn
#140016 01/09/04 08:58 PM
Joined: Dec 2002
Posts: 1,253
djk Offline
The ETCI down here doesn't allow a telephone or telephone socket in the bathroom. They suggest you bring a portable, battery powered, phone.

Voltages present on an Irish line:
On Hook:
14-58V DC
Maximum voltage for test purposes 250V DC
(current limited to 4mA into a 1k ohm resistor)

Ringing Signal:

Frequency 25Hz
Voltage :
Min: 35V
Max: 90V

However, on the public system (AXE and E10B switches) you usually find:

Frequency 25 Hz
40 V rms applied differentially on each leg, out of phase.
Cadence 0.375 s ON, 0.25s OFF,
0.375s ON, 2.0 s OFF repeated.

If caller ID is presented the first ring
will be 0.5 ON followed by 2sec second of silence.

PABXs/ISDN Terminals and other line sources may apply 70-90V to one leg only.. sometimes at anything from 20- 50Hz.

I wouldn't be overly concerned with a public line in a bathroom, except for test voltages...
~40V to ground from either wire when ringing
but 80-90V between the wires.

However, the ETCI don't consider Telephone network voltages SELV.

So, I guess normal bathroom regs would apply.

Interestingly, it's also recommended that you activate call divert to your mobile *21*moble no # before working on a phoneline...

[This message has been edited by djk (edited 01-09-2004).]

#140017 01/10/04 09:22 AM
Joined: Dec 2001
Posts: 2,498
I've got an auxiliary bell that's supposed to work on the weird voltage of 200V DC. Sounds ugly. No idea where it got the power from, it wasn't working when I found it and some wires appeared to have been cut.

#140018 01/10/04 12:25 PM
Joined: Aug 2001
Posts: 7,520
Idle battery voltage on a standard British line is DC 50V nominal, with the tip (A-wire) at ground and the ring (B-wire) at -50V. That alone would be enough to give a fair tingle to someone immersed in water.

Ringing voltage can reach over 100V on short lines or where no ringers are loading the supply, and that's superimposed on the 50V DC battery.

Cadence 0.375 s ON, 0.25s OFF,
0.375s ON, 2.0 s OFF repeated.
Minor difference in nominal specification for Britain: 0.4 on, 0.2 off, 0.4 on, 2.0 off.

Thinking about another recent thread, perhaps I should add that in the days of the former GPO monopoly on telephone wiring, there is no way they would have even considered a request for a phone to be installed in a bathroom.

[This message has been edited by pauluk (edited 01-10-2004).]

#140019 01/10/04 04:07 PM
Joined: Dec 2002
Posts: 1,253
djk Offline
Over here 48-58 V is normal... the lower voltages are mentioned as telephones should be designed to cope with those conditions.. e.g. some PABXs etc can provide weird voltages.

As for the ring cadence...

In the early 1990s we had 2 lines from two different switches in the house.

1 was AXE
the other was ARF (Crossbar)
(The AXE was actually providing trunk access etc for the ARF which was gradually, cut over to AXE one number range at a time )

The phone on the ARF line had a noticably slower ring signal.

Phoning out on the ARF was weird too.
You tone dialled the number and then got, what appeared to be a specifically generated tone which sounded like "tick-tick-tick-tick-tick-tick-tick" rather than just random switch noise and then a big "CLUNK" as it made the connection. Occasionally you'd over-hear a blast of MF tones as it signaled either internally or to its parent AXE.

The weird thing is that I used to get better modem speed on the ARF than on the digital AXE line [Linked Image]

" Ericsson was always the great innovator with R2.  In their ARF crossbar system, they used MFC (MF Compelled) to signal from the register to the individual switch markers and this too could work end to end, so these markers all appeared to act like small transit registers."

The switch wasn't supposed to let you hear this but occasionally you would hear blasts of tones...

Part of the reason for the E10 (digital switch) routing tone was to hide the in-band signalling used when talking to ARF switches.

Eircom actually developed a system in-house called "BOB" to monitor these tones and provide a full PC interface to the exchange for testing and improvements to itemised billing. ARF had to be able to handle non-unit based billing.

BTW since the early 1980s, there was no way for an ARF to communicate directly with the rest of the network they were always "parented" by an AXE or E10 switch that handled their incomming/outgoing traffic digitally. (i.e. using C7 / SS7).

ARFs are now long gone from the network.

[This message has been edited by djk (edited 01-11-2004).]

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