My friend is trying to hook up his new hp fax machine without a phone, he has a 2 pin phone cable running from his modem to his inlet line 1 on his fax machine but he can't seem to get it to work, he also does not have a wall outlet for a phone cord ... my question comes down to looking for a diagram or a brief explanation of what the 2 and 4 pin conductors mean on the phone cable

closed as unclear what you're asking by Niall C. Jul 4 '17 at 4:13

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  • Are you asking about the phone wiring as delivered by your phone company? Or are you asking about how to hook up a fax machine? – Niall C. Jul 4 '17 at 4:14


Here's a decent one-page reference, where you are probably only interested in the first paragraph and diagram about the RJ11 plug: http://www.westernet.net/Help/RJ45.htm

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Traditional telphone (POTS="Plain Old Telephone Service") uses "quad" wiring to support up to 2 telephone lines. That's the traditional telephone cable with black, red, green, and yellow wires. If you're looking at the wires in a RJ (registered jack) connector, they belong in that order. The mnemonic "BuRGundY" may be helpful. Each line uses one pair (2 wires) for a voice or fax connection.

Line one uses the red and green wires. Line 2 uses the black and yellow wires.

A single-line configuration (red/green) uses the two pins in the center of the connectors.

In a two-line configuration, the second line (black/yellow) uses the two pins to the outside of the center two pins.


DSL (ADSL, VDSL, etc.) also uses two wires (one pair), like POTS. Both DSL and POTS signalling can be transmitted on the same wires because they operate at different frequencies. But the DSL signalling causes interference with analog sound signals and needs to be filtered out. You use a DSL splitter to do this.

The DSL Modem

Your specific DSL modem might have an internal filter and might thus provide a clean analog phone jack. If not, then you need an external splitter.

If you do need an external splitter, then you need to plug the splitter into the wall, and plug the DSL modem and any analog telephony devices into their respective jacks on the splitter.

The Phone Company

You also need to have POTS service on your line from the phone company. Just because you have DSL service doesn't mean you have analog telephone service.

I don't have analog phone service from the phone company, for example. I do have a "home phone" line that I can use for the rare fax transmission, but it is connected to a VoIP device that is connected to my Ethernet network.


he has a 2 pin phone cable running from his modem to his inlet line 1 on his fax machine

A typical arrangement is something like

phone  _______ADSL ______DSL
socket       Filter      Modem

where the lines are usually all typical 2 wire cables with RJ11 plugs.

Any plain old telephony service (POTS) device, like an analogue fax machine, usually needs to be plugged into a "phone" (POTS) socket on the ADSL filter.

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