From Bare Wire to Eye-candy Resins—An American Electrical Cable and Cord Set Manufacturer Holds the Line
Posted on 11/21/22 8:21 AM
Before cord sets are ready to be boxed for shipping, the colorants used in the resins, and the shiny brass and alloys of blades and pins may often resemble an electrical work of art that catches the eye—especially the orange and red cord sets preferred by Australian and Denmark hospitals respectively. Or maybe it’s a clear molded plug, or a hand-wired plug where one can see inside to tell whether every wire retains electrical continuity around the stainless steel ring that binds the conductors. Even standard colors like black and gray offer a semblance of eye candy while manufactured to carry hundreds of volts to equipment across multiple environments.
|Resin Pellets Used in Cable Extrusion
|These finished electrical products began as reels of copper, pellets of resin, stainless steel or alloy screws and fasteners, folded brass and other alloys, bridges, strands of Kevlar, fuses, and the multiple processes on multiple machines to extrude (insulating and jacketing), cable (in part via a rotating capstan), mold, cut, strip, crimp, ultrasonic weld (metal and plastic), label, hank, and tie. There are also numerous stations along the way just on the extrusion line: multiple laser-measuring stations, a wire-cleaning station, extruders 1-3, a talc station, spark testers, a water-cooling station, and a drying station.
Inventions that changed the world are too numerous to list: fire, the wheel, gun powder, the printing press and the steam engine, the pencil and the light bulb, and likely somewhere down the list is the bare copper wire. Copper is an iconic conductor with many great properties—corrosion resistance is high among them, and copper is still a popular conduit for water.
The Extrusion Line: A Magical Mystery Tour
One reel at a time, the copper conductor wire unspools with the aid of a clipper lift inside a “bug eye” which allows the wire to unspool its hundreds of pounds while keeping square to the extrusion line. The unspooling of cable down the line relies on a tensioner on one end and a take-up or accumulator on the other end to maintain the necessary tension as to complete the extrusion process.
As the bare wire speeds down the line up to 1,000 feet per minute, its diameter is continually measured by multiple readers using lasers integrated with computer hardware and software which measure to 1/10,000 of an inch. The bare copper wire is cleaned along the line before being extruded in resin by extruders 1-3. Extruder 1 contains the natural, light-colored material while extruders 2 and 3 extrude separate colors such as blue and brown to coat the bulk of natural resin material from extruder 1—colors are alternated from extruder 2 to 3 by turning a switch on the crosshead.
The insulated wire is measured before and after extrusion while “hot” and measured after cooling “cold” once immersed in a water trough via a filtrated chiller. Laser measurements are taken multiple times along the extrusion line to meet worldwide agency standards (diameters).
The various colors designate ground, line, and neutral conductors according to North American, international, and Japanese colors per their agency standards. However, four- and five-conductors may be required for larger cable diameters, requiring even more natural resin from extruder 1 during the jacketing process. The insulated wire maintains agency diameter specifications due to the laser measurements which regulate and adjust in concert with dry and wet capstans, which are vertical drums spinning the cable faster or slower to reduce or add material to meet preprogrammed diameter specifications.
Bare copper is never spark-tested due to the nature of copper and electricity, but once insulated, the wires are spark-tested for holes or gaps in the natural material.
Jacketed Wire (Cable)
Once the separate insulated wires spool onto the take-up, the individual spools run through the rotating capstan connected to the cabler, and strands are “bunched” into a length of lay: the length of one colored wire woven under another colored wire (visible to the eye) is one definition of the length of lay. The length-of-lay makes the bunched wires more flexible which helps preserve the electrical continuity of its conductors.
Before being jacketed, the bunched length-of-lay conductors are coated in talc (for easier wire-stripping by the customer) before being jacketed in natural resin and a single layer of colorant. Extruder 1 is the workhorse for jacketing since cable requires much more natural resin than colorant to hold the conductors in place while remaining flexible. The single layer of colorant is added onto the wall of the cable for identification (line, neutral, ground, etc.).
The jacket runs through a printer down the line to receive agency (UL/CSA/VDE, etc.) file numbers and approval marks, voltage and flammability ratings, jacket material, e.g., “SJT” and sizes in AWG and mm along with the manufacturer (Interpower). The cable is now ready to be reeled onto a wooden spool where it is wrapped in plastic and properly labeled. The cable is now ready to be shipped.
Key Cable Factors Already Determined
While the above process is used for both North American and international cable, the materials, e.g., resins with certain characteristics according to the environment for which it will be used, will have already been determined before the first foot of cable is manufactured.
If the market is North America, then North American approved cable needs to be used. If in Germany, then international-approved cable must be used. If China, the cable must meet Chinese standards requiring approvals from a Chinese agency—the market where products will be sold (North America, Europe, Asia, or South America) determines the type of cable and agency approvals needed. Typically, countries have their own agencies: the United States (UL), Canada (CSA), and Germany (VDE), to name a few.
Environments for Cable Use
One main factor in determining cable type is the immediate environment. A household appliance requires a different jacket than a jacket used for industrial use. If used outdoors, one must consider abrasion, heat, and humidity. And there's no need to rush out and reinvent plastic since UL's iQ site offers many resin "recipes" already approved, saving manufacturers the cost of sending samples for agency testing unless specialized blends are needed, such as adding unique materials to reinforce polymers or adding UV stabilizers.
North American Cable
North American cable is sized in American Wire Gauge (AWG), which uses an inverse relationship to size—the larger the number the smaller the cable. Cable for single-phase applications will be either a 2- or a 3- wire variety. A 2-wire cable is for Class II (ungrounded) applications while 3-wire cable is for Class I applications, which require a ground. Three-phase applications require either a 4- or 5-wire cable.
Basic Cabling Material
|Thermoplastic can be softened through heating and hardened through cooling. It can be molded when heated and can retain its shape after cooling. Thermoplastic is the opposite of thermoset.
|Thermoplastic or TPE is a material that has characteristics of rubber as well as thermoplastic.
|Thermoset uses a heating process—curing—and once the plastic is cured, it can't be altered from its original state.
|PVC is a common thermoplastic material for cable and conductor jackets and some molded plugs.
|Rubber is also a common material for cable. It is a thermoset-type material. While it may be more costly than thermoplastic cable, rubber is extremely durable. Rubber is a good choice for outdoor applications.