Path: utzoo!telecom-request Date: 26 May 91 02:49:15 EST From: "Barton F. Bruce" Newsgroups: comp.dcom.telecom Subject: Re: Why a Twist in Modular Cables? Message-ID: Organization: Cambridge Computer Associates, Inc. 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 398, Message 5 of 10 Lines: 32 In article , rees@pisa.citi.umich.edu (Jim Rees) writes: > Can anyone tell me why there is an electrical twist in most (US) > modular cables? > 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? The wall to the phone cords have the wires flipped, and early on ModTap had made EIA to modular adapters for such cables, but soon realised their mistake and stopped. Many people have modular patch panels and can route EIA signals from one part of a building to another. There is NO way be be sure there will be an odd or and even number of cords in between. If the plugs are crimped on so the wires go straight through, and all adapters are wired that way, you will have no problems. That is the way the DATA industry generally does it. In many sites 'PHONE" cords have caused needless confusion and are BANNED. With polarity guards built into modern TT dials, and ringing being across the line and not to ground, many sites make life simple and ALL modular cords, both EIA DATA and 'phone' cords are wired straight through. FWIW most folks use six or eight wire cords for everything, and cords that come with phones are generally four or even two wire, so the problem ones are easy to spot.