Ground wire?

[timmerk]

I'm setting up a payphone and connecting to a coin line (emulated). From what I understand, I need tip, ring, and I believe a ground connection, otherwise the relay won't work. I was hoping to use one of the extra wires in a standard phone line wire as the ground, but I read somewhere that it should be 18 GA or larger. Can anyone confirm the size I need, or if the small gauge (22 or 24 I'm guessing) wire will work? Thanks!

[poplar1]

I don't know how large the ground wire needs to be. If you use two 22 gauge wires (say yellow and black) twisted together, they are approximately equivalent to one 19 gauge.

[dsk]

It is an idea about protection against electrocuting.
In your phone system, does the ground wire carry any current at all?
My phone uses a 100V DC for the relay, and  I just use a third wire, but the entire system is insulated from ground, so if I hold on a live power wire with one hand, and in the phone with the other it will be quite safe until it pops up an error on my payphone line system.

If my system was connected to ground, the ground wire should have been thicker than the line, and I would probably had a GFCI in the supply. In that case be aware of that many GFCI's does not "see" DC currents.

dsk

[Key2871]

I think the minimum should be 10 gauge.
To protect against any fault potential.
You really don't want to skimp on grounding when your talking about high voltages, DC especially.

[Jim Stettler]

I think it just needs a ground reference vs being electrically grounded.
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Stan's controller uses a 4 conductor line cord between the phone and controller.


Here is a link to an active auction.
https://www.ebay.com/itm/304107952490?

from the description:
Tip, Ring and Ground are the only connections between the payphone
and the controller.
They are made using a standard modular telephone cord.

The controller uses a 9 volt wal-wart transformer (no ground prong.

Jim
                                                           
There is a lot of good info in the description


Most of the hobby payphone controller circuits use a capacitor to kick the relay

[dsk]

I did also just use a capacitor in my d.i.y. controller. Works well on an ATA with polarity reverce when party answers..  http://www.classicrotaryphones.com/forum/index.php?topic=11987.msg127999#msg127999
dsk