Phone Cables for Fax Machines

[Jeff Orum]

I've found that the phone cables supplied with fax machines, at least in
two cases, don't reverse the lines as regular phone cables do.

Some more details:

The standard 4 wire phone cord that plugs into the RJ11C jack and into the
back of the phone reverses the leads.

End 1 End 2

| | | | | | | |
1 2 3 4 1 2 3 4

i.e, position 1 at one end is the same wire as position 4 at the other end and
position 2 at one end is the same wire as position 3 at the other.

On both the fax machine I have at home, and another brand that is here at work,
the phone cord that comes with them has the RJ11C plugs, but only 2 wires, at
positions 2 and 3 (I realize that there are only 2 of the 4 lines in the RJ11C
used, so having only wires at positions 2 and 3 will work for a standard
phone line and connections). The strange thing is that position 2 at one
end is the same wire as position 2 on the other, and not position 3.

I found this out because I used a regular cable to hook up my fax machine,
and found the output on the fax machine (to connect either another phone or
an answering machine) to be the wrong polarity, using my handy dandy telephone
line tester. Using the supplied 2 wire cable corrected this problem, but
I am curious. Clearly the fax machine is designed to use a cable that
does not reverse positions 2 and 3, but why? Why not just make the machine
like every other piece of phone equipment I have seen?

Jeff Orum
or...@cup.hp.com