>>> In such situations, I tend to put them in resistor color code order. >>> In this case, from low to high: yellow, green, blue, white. >> Resistor code is the only standard... > I think there's a standard for telco wiring as well. Don't know > what it is, though. It tends to tell you which wires are paired... Telephone standard practice has used the same color code for at least 25 years (that I've been working with it). It is an extensible standard that goes up to (at least) 625 pairs. I think it goes beyond that, but I've never worked with a cable larger than 600 pairs (or even nearly that big). There are 5 wire colors -- blue (bl), orange (or), green (gr), brown (br), & slate (sl) -- and 5 group colors -- white (wh), red (rd), black (bk), yellow (yl), & violet (vi). 25-pair is the primary unit. Each pair is identified by the combination of a group color plus a wire color. For example, the 1st pair is white/blue (wh/bl), 2nd pair is white/orange (wh/or), ... 5th pair is white/slate (wh/sl), 6th pair is red/blue (rd/bl), ... & 25th pair is violet/slate (vi/sl). If a cable has more than 25 pairs in it, each 25 pair bundle is held together with a colored binder over-wrap. The binder is the group color (or group+wire) color. First 25 pairs use a white (or white-blue) binder. Second 25 pairs use a red (or white-orange) binder. You can easily extend this up to 625 pairs (25 bundles of 25 pairs). For example, a 100 pair cable will have 4 bundles of 25 pairs. First bundle will usually be wrapped in white+blue nylon binder. Second bundle is in white+orange binder. Third bundle is in a white+green binder. Fourth bundle is in a white+brown binder. Old cables had solid color wires. The first pair was a solid white wire twisted with a solid blue wire. You never untwisted a pair until you were ready to punch it down because you lost the "pairing". New cables (last 20 years or so) have each wire more uniquely marked. Each has a primary color with a spiral marker color. The first wire of first pair is mostly white with a blue spiral. Second wire is mostly blue with a white spiral. Much nicer to work with since you can untwist and fan out an entire cable without losing information. [ Practical note: tiny spirals of orange and brown look an awful lot alike in a dimly lit, dusty telco closet. Have a bright flashlight or a work light handy. :-) ] To identify individual wires, the group color wire is first. 1st wire of 25 pr bundle is white wire of white/blue (1st) pair. 2nd wire of 25 pr bundle is blue wire of white/blue (1st) pair. 13th wire of 25 pr bundle is red wire of red/orange (7th) pair. 14th wire of 25 pr bundle is orange wire of red/orange (7th) pair. 50th wire of 25 pr bundle is slate wire of violet/slate (25th) pair. Individual wires are almost NEVER used -- use is _always_ in pairs. Normally, 25 pair cable is terminated on a punch-down block; either 66B style (6 position wide x 50 wire long), 66M block (4 position wide x 50 wire long), or 110 block (various types). Usually, a 66M block is vertically oriented. Commonly each 66M block in a telco closet or central office, containing 25 pair (50 wires), is punched up as follows from top to bottom: 1 white/blue wh/bl blue/white bl/wh 2 white/orange wh/or orange/white or/wh 3 white/green wh/gr green/white gr/wh 4 white/brown wh/br brown/white br/wh 5 white/slate wh/sl slate/white sl/wh 6 red/blue rd/bl blue/red bl/rd 7 red/orange rd/or orange/red or/rd 8 red/green rd/gr green/red gr/rd 9 red/brown rd/br brown/red br/rd 10 red/slate rd/sl slate/red sl/rd 11 black/blue bk/bl blue/black bl/bk 12 black/orange bk/or orange/black or/bk 13 black/green bk/gr green/black gr/bk 14 black/brown bk/br brown/black br/bk 15 black/slate bk/sl slate/black sl/bk 16 yellow/blue yl/bl blue/yellow bl/yl 17 yellow/orange yl/or orange/yellow or/yl 18 yellow/green yl/gr green/yellow gr/yl 19 yellow/brown yl/br brown/yellow br/yl 20 yellow/slate yl/sl slate/yellow sl/yl 21 violet/blue vi/bl blue/violet bl/vi 22 violet/orange vi/or orange/violet or/vi 23 violet/green vi/gr green/violet gr/vi 24 violet/brown vi/br brown/violet br/vi 25 violet/slate vi/sl slate/violet sl/vi The binder over-wrap, cut off during the punch-down process, is frequently tied around one of the top corners of each 25 pair block to identifiy each bundle in a 50 or 100 pair cable. 25 pair cables used to be quite common in offices when each desk phone was a 1A2 key system multi-button phone. This took a 25 pair cable going from the telco closet out to each desk! Now, the desk phone signalling is all digital on 1 or 2 pairs. The 25-, 50-, and 100-pair cables are only used between distribution frames, between floors, and on backhauls to the central office. Notice that normal 4 pair UTP cable used for Ethernet shows it's telephone company heritage because it follows the color code of the first four pairs as listed above. Lee Jones -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads