I've googled for it but am trying to find a chart that shows capacitance per thousand feet of varying types of cable but most specifically 24 awg outside plant twisted pair.
One of our new DSLAM's only shows capacitance on the line test but our old gear showed an estimate of distance based on that capacitance.
I don't think there is such a chart. You'd need a kick meter like a side kick to get what you're looking for. How are you measuring the capacitance?
Our Adtran equipment will show us the capacitance on a loop test:
Tip-Ring 33 nF
Our older equipment gives an estimate of distance based on capacitance.
You're looking for converting the MF to feet. I don't know of any such chart. Do you have a TDR test set? All kick meters, open locators use Capacitance to estimate the number of feet.
We have equipment that will do it but this particular box is located in central offices. We want to be able to do remote testing and not drive around town to test pairs. I'll just use one of our meters on some known lengths.
Thanks
I found a couple of complicated formulas, but no charts. I did find one old document that said there's 08mf in a mile of cable, but it didn't specify gauge and it was on submarine cable. Also your reading was in nanofarads which you'd have to convert to microfarads to match any test set you're using. I think I'd just break out another test set.
To get a relative value, you could use an old analog ohm meter. We used to use a Simpson 260 from the CO to test a pair for opens before going out to troublshoot in the field. You need a meter with a switch to easily reverse the connections to tip and ring, so you can compare the capacitance kick from each side of the line. After you get to know your cable plant, you can get pretty good at knowing which ped to start in.
Jim
I don't want to go to the CO each time we have a line problem. We're a CLEC and aren't allowed to open peds or make OSP repairs. Our main use for this test is to see how long the loop is so we can see if someone pulled our jumper in the crossbox or at the CFA or if there's a real problem with the circuit that we need to call in to Qwest.
Capacitance is tricky. First off, just knowing the gauge of the subject cable does not tell you enough. The capacitance is determined by how much plastic is in the cable, and this varies wildly for different cable types. The insulation of the individual conductors is what matters: the type of plastic, and whether it is solid core, foam core, or air core [1].
Using something like an open meter [or any other piece of test equipment that attempts to determine distance based on capacitance] requires pre-calibrating the equipment using a known length of cable, if you want real accuracy. That said, the documentation for some open meters does include a chart of typical capacitance for popular cable types - which is to be taken with a grain of salt. Manufacturer's data for new OSP cable almost always includes nominal design capacitance values for the individual pairs [tip-to-ring value], pair-to-pair, and also pair-to-sheath. These numbers can be fairly accurate for brand new cable [capacitance changes with age], but a good OSP engineering department will still take capacitance readings on known lengths of newly installed cable for future reference.
Your best bet is to take measurements on known lengths of cable and create your own chart for each type of OSP cable in your plant. The typical plant often includes many transitions between cable types, so any existing plant records should be dug up, if possible. This makes your job way more interesting!
[1] The term "air core" in this case refers to the individual conductors. Today, "air core" is used to mean any OSP cable that is not filled with icky-pic or other filling compound. The original meaning of the term [as used in this discussion] refers to a design where the insulation on the conductors had tiny splines on the inside, reducing the amount of plastic used in an effort to reduce capacitance. This has largely been replaced by foam-core insulation. No, I didn't make this up. Honest.
Jim
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Speaking from a secure undisclosed location.
Sorry, I was still typing when you made your last post - I didn't realize you represented a CLEC. Your hands may be tied on this, depending on how much cooperation you can get from Qwest.
Jim
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Speaking from a secure undisclosed location.