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Teflon insulated wire is wonderful stuff. If you are accustomed to fighting insulation melt-back with ordinary PVC hook-up wire, you are in for a treat when you try Teflon (you cannot hurt it with a soldering iron). Teflon wire has been used in downhole logging tools almost exclusively since the 1960s because of its excellent high temperature performance. Some manufacturers have also used it in logging surface electronics. AnaLog Services, Inc. uses Teflon wire for all well logging electronics applications. Extruded Teflon (polytetrafluoroethylene or PTFE) insulated hook-up wire comes in three main flavors: the more commonly encountered Type E, rated for 600 volts (historically M16878/4), the slightly thicker Teflon jacketed Type EE, rated for 1000 volts (historically M16878/5), and the rarely seen very thin insulation Type ET, rated for 250 volts (historically M16878/6). All three types are silver plated and rated for use up to 200°C. Other specs cover the 200°C wrapped Teflon insulated wires, and the 260°C extruded and wrapped nickel plated wires. To minimize rambling, the balance of this effort is limited to extruded Teflon single conductor wire, often referred to as Teflon "hook-up" wire. |
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Type E |
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600 Volt |
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Type EE |
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1000 Volt |
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Teflon wire is available in a wide variety of colors. For the most part, the well logging industry has adopted the color code scheme used by the military. Said scheme uses the same numbering as resistor color codes, with black = 0, brown = 1, red = 2, orange = 3, yellow = 4, green = 5, blue = 6, violet (purple) = 7, gray (slate) = 8, and white = 9. There has been less agreement historically within the logging industry over the numbering scheme for the multi-colored striped wires. Unfortunately, the wire manufacturing industry has never established standards for color shades; actual wire colors vary over a wide range. Some of the Teflon wire insulation colors can be very pretty, almost with a glowing or neon quality. See also Surface Wiring Color Codes and Downhole Wiring Color Codes and Tool Connector Pinouts. Teflon wire is usually silver plated, as is most wire rated for use at over 125°C. At high temperatures, and over time, tin plating or solder tinning can dissolve into the underlying copper wire, leaving a surface that is difficult to solder. Silver plating can withstand higher temperatures for longer periods of time than can conventional tinning. Further, at the temperatures Teflon insulation is extruded and cured, individually tinned strands would be effectively soldered together to make a solid wire. Freshly stripped Teflon wire is truly beautiful with its white silver luster. But silver plated wire tarnishes (just like silverware); it should not be stored near sources of sulfur fumes such as cardboard, paper, rubber bands, etc. Teflon insulated silver plated copper wire is fairly immune to tarnish, but sometimes it is necessary to cut off and discard an inch or two if discoloration is seen at the end. Nickel plating is used for temperatures exceeding 200°C, but nickel is more difficult to solder due to surface oxidation. Interestingly, because of the difficulty in extruding long runs of Teflon insulation, the mil spec allows a large spool of Teflon insulated wire to be made up of several spliced pieces (the hydraulic extrusion rams can only hold so much Teflon material, thus limiting the maximum uninterrupted producible length). Only stranded wire should be used in well logging electronics. Long experience has shown that solid hook-up wire fails long before stranded wire, probably because of vibration during transport more than anything else. However, improperly stripped (nicked) stranded Teflon wire often fails at the connection point. (An alternative theory holds that these failures are related to solder wicking up the silver plated wire strands, but proper stripping seems to eliminate most of the failures.) A common complaint heard about Teflon wire is that it is hard to strip. Most authorities recommend expensive automatic stripping tools with special Teflon insulation cutting dies installed. These gizmos cost a small fortune, we hate their cumbersome action, and they do not always do such a great job. Teflon insulated wire is expensive, several times more expensive than ordinary PVC insulated wire. One manufacturer's published literature states the cost is eight to ten times as great. Fortunately, there are reputable vendors with good quality Teflon wire at half or less the cost of the big boys (Belden, et al.). Further, Teflon wire is available in the surplus marketplace, though not all wire gauges, stranding options, or insulation colors may be available at any given time. Unfortunately, in recent years, the audiophile community has driven surplus Teflon wire prices up considerably. These folks believe they can actually hear an improvement when audio equipment is constructed with Teflon wire. This is of course utter nonsense, but they sure buy a bunch of Teflon wire, thus driving up the surplus prices. |
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See also Teflon Tubing Trivia. 03-04-02 |
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