After World War II, America saw the rise of multiple industries including electronics, which grew 400% in a ten-year span (1945–1955). Appliances such as hard-wired and transistor radios, televisions, refrigerators, and washers were driving demand, and electronics in automobiles and campers. The race to modernize carmaker assembly lines was on as well. The shift from soldering to crimping (including the specific B-crimp style) for electrical terminations in the 1950s was driven primarily by the need for high-reliability applications such as military and aerospace wiring—and soldering was becoming less of an option heading into the jet age.
The problem with molten solder on stranded wire is how the wires become brittle once cooled, which is a weakness especially at stress points—engine and motor wiring, manufacturing equipment and heavier appliances become susceptible to electrical failure. Brittle wiring is prone to cracking when attached to machines and devices which continually flex or vibrate.
Out of necessity the B-crimp was born to ensure stranded wires provide reliable electrical continuity—75 years later it’s still reliable. A proper B-crimp (especially "gas-tight" designs) creates a weld-like bond between the wire and terminal without heat, preserving wire flexibility and distributing stress more gradually while providing better mechanical resistance to vibration. Also, crimped connections are more repeatable and reliable when done with the right crimping tools, which reduces errors in production lines. They enabled faster, automated or semi-automated assembly, which was vital as electronics production boomed post-WWII.
The hexagon crimp is an alternative to the B-crimp, but is one better than the other? Laboratory test results reveal the hexagon crimp design (its hexagon shape versus the compressed polygon of the B-crimp), raises terminal temperatures in flexible cable upwards of 170°C while comparatively the B-crimp’s temperature rises upwards of 115°C, which is significant since it is not optimal for terminal temperatures to rise above cable temperatures (120°C.) That the B-crimp keeps its cool while the hexagon crimp raises terminal temperatures above cable temperatures makes the B-crimp the superior choice of the two for flexible cable, especially where fire safety is concerned. However, the hexagon crimp performs well with rigid cable, with cable and terminal temperatures testing out at 120°C and 110°C, respectively. Also, flexible cable, when B-crimped, has more compression (with characteristics closer to a solid wire) offering better conductivity.
Interpower North American and international cords are composed of insulated conductors of stranded wire bunched into a “length-of-lay”: imagine a thin white line on top of the green conductor wire as it enters the rotating capstan of the cabler. When the wire undergoes a complete revolution or “lay,” that white line has made one complete revolution and is now back on top the way it entered the capstan. All three conductor wires complete these full revolutions as to be “flexible” wires and eventually a flexible cable for cords after a final full extrusion of the jacket.
Again, this greatly increases the flexibility and strength of the jacketed cord, such as Interpower’s three-conductor NEMA 5-15 and 5-20 standard or hospital-grade cords—every Interpower cord is manufactured with length-of-lay conductors.
In the American electrical industry, the tradition is to manufacture American Wire Gauge (AWG) cable in even numbers, e.g., 12, 14, 16, 18—the larger the gauge, the smaller the cable. The number of strands inside a conductor isn’t selected randomly, but by design. Let’s say you want to make 18 AWG cable. Your strands of wire must equal the cross-section of one solid 18 AWG wire—in other words, its circular mil area (CMA). For 18 AWG, the CMA is calculated by converting its diameter into a square-inch figure (0.0403 which converts to 0.001276 sq. inch). The circular mil area of a circle is a diameter value of 0.001—so how many of those 0.001 circles fit into a 0.0403 circle? The CMA of 18 AWG, then, is derived by dividing 0.001276 by 0.000000785, which puts the CMA at 1625. The strands of wire, whether 7, 16, 19, 41 or 65 (for 18 AWG), must be made within 2% of the solid wire equivalent, or within a minimum of 98% of the solid wire’s total CMA.
The fewest number of strands for 18 AWG is 7, with 6 strands surrounding the center strand (nucleus) in a hexagonal shape despite its round appearance. Seven-strand wire contains 6 interior voids (spaces) and 6 perimetric voids, i.e., 6 spaces around the nucleus strand, and 6 spaces outside the perimeter strands. Another stranding combination for 18 AWG is using 19 strands, which contains 24 interior voids and 12 perimetric voids. All strand centers lie on a hexagon. By compressing the B-crimp in the crimping tool, the B-wings spread over and into the crimp, thus compressing the strands enough to form hexagonal shapes like a honeycomb. Now the CMA is similar to a solid conductor’s surface—it provides a very solid and clear electrical pathway. The difference is what was once a “line” contact is now a “solid” contact via adjacent round strands now forming a flat, polygonal surface.
In 1995, engineer John D. Butler wrote about his crimp calculations and ratios using his proprietary “B-CRIMPCAD” software. Using a 16 AWG conductor with 26 strands, he found that a crimp width of 0.141 and a crimp height of 0.080 has a crimp area reduction (CAR) of 17.3%, which falls into his target area of 15–20%. The crimp height divided by the crimp width is 0.55 (55%), again falling in line with the targeted 50–70% range. The tested crimps adhering to this range showed no voids or cracking; they all showed good electrical performance and pull-test resistance.
At a UL 1659 Meeting in Fort Lauderdale, Florida, in 1998, Butler presented his crimp “manifesto”: “B” Crimp Tolerances and Their Effect on Crimp Compression. At that time, the industry had different views on how to get the most out of a B-crimp, such as a crimped connection that exhibits a high mechanical pull strength should result in good surface contact between the conductor and terminal while providing good electrical performance. And, knowing the physical dimension of the crimp height that passed a high mechanical pull test, one could simply measure crimp height to determine pull test success while also meeting the electrical performance criteria. Not so fast.
Butler knew pull test success and crimp height were only two components of a broader solution.
Interpower Corporation is an electrical power cord and component manufacturer headquartered in Oskaloosa, Iowa, with production and testing facilities in Lamoni and Ames, Iowa, respectively. Interpower is a premier supplier of power cords and power system components worldwide, celebrating its 50th anniversary in July of 2025.
For more information on this product or our complete line of products, please contact our Customer Service Department at (800) 662-2290, or at info@interpower.com, where you can interact with staff including a technical expert to walk you through questions.