Path: utzoo!telecom-request Date: Thu, 23 May 91 13:51:12 GMT From: rees@pisa.citi.umich.edu (Jim Rees) Newsgroups: comp.dcom.telecom Subject: Why a Twist in Modular Cables? Reply-To: rees@citi.umich.edu (Jim Rees) Message-ID: Organization: University of Michigan ITD Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 394, Message 4 of 10 Lines: 17 Can anyone tell me why there is an electrical twist in most (US) modular cables? Every ready-made RJ-11 cable I've ever seen has the plugs attached on the same side of the cable at each end. This results in an electrical twist in the cable, so that pin 3 at one end is connected to pin 4 at the other. For phone line use this is usually not a problem, but I just wonder why they don't put the plug on the other way around at one end, to make a straight cable. I got to thinking about this recently when I started using these cables for RS-232. If you're clever about pin assignments, this twist can be useful for RS-232. So is there a reason for it, or is it just manufacturing convenience?