J.B. Wood wrote:
On 02/08/2011 07:31 PM, Jim Thompson wrote:

I wasn't clear...

What I'm driving at, can I run a ringer from Ring to Earth ground?

(I don't have enough pairs :-)



Jim, did you finally get some useful info? Assuming that Verizon and
others for traditional analog telephone service are following the old
Western Electric (Ma Bell) standards, then the on-hook DC voltage
between Tip and Ring should be nominally 48 VDC. If you measure (either
Tip or Ring - I don't remember which one) to earth ground you will also
see 48 VDC since one side of the central office battery is connected to
earth ground. From an AC (voice frequency) standpoint both Tip and Ring
are balanced to earth ground (for hum reduction) with a nominal line/set
impedance of 600 ohms. The AC and DC aspects of the line are kept
isolated via chokes and/or repeating coils, which are required in a
common-battery (as opposed to local battery) telephone system in order
to prevent the shorting out of the audio by the central office battery.

Now in "ancient" times two-party line ringing was accomplished by
connecting the phone's ringer from Tip-to-earth ground on one
subscriber's set and from Ring-to-ground on the other subcriber's set.
This also had to be wired appropriately on the central office's ringing
equipment. Connecting subscriber set ringers in this manner adds a very
slight amount of hum due to the unbalancing of the phone line (but not
much due to the ringer coil high impedance).

AFAIK all ringing these days is bridged (ringer connected Tip-to-Ring)
so ringing-to-ground would probably not work. This is also worth
remembering if you ever desire to hook-up an antique phone (e.g. a WE
type 500 or 2500 set) to your phone line and find the ringer
non-operative (unless you want it that way). The ringer should be
connected to the incoming phone line red and green wires with no ringer
wire connected to the yellow or black one. Sincerely,


I've read all the answers so far looking for mentions of hum and this is
the first I've seen. As I recall, there is an earth ground rod at the
entrance, but the installer can tie it to either line of the balanced
pair to minimize hum.

Ring voltage used to be about 90 volts - can you use a bridge rectifier
feeding a voltage comparator to detect it, then some dc circuit to
ring.? 48 volts is normal idle, the phones are low enough inpedance to
drop it near 0 when off hook, but the ring voltage emulates the old
hand-cranked generators with about 90 volts AC out.

Then again, I've never worked for a phone company and haven't tried this
stuff since the 70s.

Alan

This is a pretty neat group.