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I am trying to connect a hardwired 2554 telephone set. There's only a few inches of slack wire coming out of the phone since it appears it was just cut there. I managed to get about half an inch of the coating cut out and then stripped the individual conductors for green, red, yellow, and black. I then connected mini-grabber leads from each and put them onto a breadboard, with green and yellow connected and red in its own row. My plan now is to use another set of mini-grabber leads to connect the green/yellow row from the breadboard to TIP and the red row to RING on a butt-set adapter I have which will get plugged into the phone line.

Far from optimal, but I don't have a free connection block at the moment and this seemed like a quick and dirty hack which ought to work.

On second though, I have reservations. I did some research and am having second thoughts. Some sources say breadboards can handle only 5V safely, others say that up to 50V at 0.5A should be fine.

Then, there's minigrabber leads, which are consistently rated for 30V AC or 60V DC. 30V AC is well below minimum ringing voltage, which is around 90V AC, give or take a dozen volts.

I believe ringing current is either 48mA or 480mA, less than half of the 0.92A limit for 22-guage wire. But strictly speaking, I'm not using any 22-guage wire, I'm just using minigrabber leads through a breadboard.

I called another telco guy I know and he said it should be fine, and not to worry about the 30VAC/60VDC limit for mini grabber leads since that's assuming a much higher current, but his analysis was mostly to the effect of "the wires in minigrabber leads and breadboards are thicker than 22 guage wire, you should be fine". Quantitatively, I can't find a good answer. I don't think this will blow anything up necessarily, but would there be any reason to be concerned about the setup (mini-grabber leads + breadboard)? I recognize the setup is far from ideal, but is there any real danger to this or not really?

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  • \$\begingroup\$ What do you mean by "safe", and how critical is a failure? \$\endgroup\$ Apr 7, 2021 at 17:29
  • \$\begingroup\$ The red/green/yellow/black wires just go to a screw terminal block inside. It's easy to attach new wires of convenient length. \$\endgroup\$
    – Duston
    Apr 7, 2021 at 19:05
  • \$\begingroup\$ @ScottSeidman Safe means that if I leave the circuit alone and don't touch it, all will be fine. I'm not including deliberately or accidentally touching it, since that would be dangerous as long as there are exposed wires. \$\endgroup\$ Apr 7, 2021 at 19:22
  • \$\begingroup\$ @Dutson Yes, but I'd rather not take it apart and do that and just use the existing wire for now. I don't have the spare parts necessary for that. \$\endgroup\$ Apr 7, 2021 at 19:23
  • \$\begingroup\$ @Jasen What part of "hardwired" is not clear to you? There is no modular jack, it is not a modular phone. Hence why I am doing all this in the first place. \$\endgroup\$ Apr 7, 2021 at 23:51

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In Europe the ring signal is 90 Volts RMS.

DC voltage greater than 50 V or AC peak voltage greater than 42 Vpeak are considered hazardous by IEC and by UL.

That means that you have to be careful.

Back in 1999 while I was prototyping a 2400 bps modem based on a TDK integrated transceiver, I got the ring signal on my fingers and I can tell you that it wasn't nice.

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The ringer voltage (90V AC) is considered non-touch safe, so it needs to be isolated so that you can’t come in contact with it. It is current limited though, so even if you do touch it it’s less hazardous generally than touching an AC power line.

Noting the limited current for both ringer and switch-hook sense, 22ga wire is fine.

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  • \$\begingroup\$ Thanks, I think 22ga is similar (if not the same) as telephone wire, but I'm not using 22ga wire, hence my question. I'm not worried about it being touch safe (I know that would be painful!) but if the circuit itself and its properties are OK to have. \$\endgroup\$ Apr 7, 2021 at 19:21

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