We left off last month preparing a fiber optic cable for termination. We were at the point where we had slipped the strain-relief boot and crimp sleeve over the cable jacket if we were using a simplex cable and sorted out the tight buffer fiber we were going to terminate out of a distribution cable.
If you are terminating a 3 millimeter jacketed simplex or zipcord cable, you will need to strip the jacket and cut off the aramid fiber strength members. You need a guide to stripping the cable jacket and cutting the aramid fibers to the right length for the connector you are using. That guide should come with the connectors.
Cutting and stripping the cable jacket can be done with a special fiber stripper, or a properly set wire stripper, as long as it does not damage the fiber. Some fiber strippers have grooves for both the jacket and the fiber, making them more convenient. Special ultrasharp scissors are needed for cutting the aramid fibers. Don’t use them for cutting anything else because it will dull the cutting edge and ruin them.
Now we are ready to strip the fiber. This is an important step where you have to choose the tool you use. Three types of fiber optic stripping tools are commonly used, and they are typically known by their brand names: Miller, No-Nik and Microstrip.
Millers look like wire strippers and are quite rugged, but they require some technique to use. Millers are not convenient for left-handed users because they have to hold them at an angle. Fusion-splicer operators generally prefer the other two strippers because they require less technique and can strip longer lengths of fiber at one time. All tools require careful cleaning to ensure proper stripping.
Stripping the fiber takes a certain amount of pulling to remove the buffer coatings. You hold the stripper in one hand and the fiber and/or cable with the other. Wrapping a few turns of the fiber or cable around a finger will help hold it securely without risk of damage.
Let’s use the Miller stripper so we can illustrate the technique. You have to hold it at an angle to keep from bending the fiber and breaking it. That is obvious when you use it. If the fiber bends when you clamp onto it, change the angle of the tool. Clamp down firmly so it will strip cleanly. To strip, slowly and smoothly push the stripping tool directly away from you.
You may notice some residue left on the fiber after stripping the 900-micron colored plastic buffer coating. That is the primary buffer coating, 250 microns in diameter, left when the stripper did not cut through both layers of coating. Clamping down firmly should remove all of the residue. If you see some of the inner buffer, strip again, cutting through all the buffer coatings by firmly clamping the stripper. If you do not remove all of the buffer coating, the fiber will not be able to be inserted into the connector.
Sometimes you will break the fiber. If you break off too much, you will have to strip the jacket of the cable back enough to start over.
Why does the fiber break? There are three possible causes: a brittle fiber, the stripping tool or bad stripping technique.
Fiber can become brittle if exposed to the air for a long time. If you are terminating a cable that has been sitting around for a while, test it to see how well it strips. If it seems brittle and hard to strip, cut off a few feet and try again. Needless to say, check for brittleness before installation and before you try to terminate or splice it.
Fiber-stripping tools, if properly cared for, are durable, but they get dirty. Bits of buffer can clog them and cause fiber breaks. Always clean the tool before use, and beware of cheap tools. Some instructors at schools approved by The Fiber Optic Association have purchased cheap strippers and found they were defective counterfeits of U.S. name brands.
You know how to perfect your technique—practice! Practice until you can strip consistently without problems. Do it in your office or lab when you have plenty of time. You have the next month to practice before we discuss attaching the connector in the next column.
Visual aids can help you learn these procedures. You can find those on the FOA online guide at www.foaguide.org.