Preformed double-dead-end grips are capable of securely holding conductors in power lines and withstanding tension loads often reaching tens of kilonewtons. The secret to this gripping power lies in a seemingly simple structure: the helically wound preformed rods.
Three Sources of Gripping Force
I. Radial Clamping Force Generated by Helical Winding
When the legs of the preformed dead-end grip are wound together, they form a hollow tubular structure. As this tube wraps around the conductor, its helical shape naturally creates a centripetal contraction tendency. When tension is applied to the conductor, pulling on the grip, the tendency for the helical rods to tighten increases-a classic "tightens-as-you-pull" effect. Unlike bolted clamps that rely on point-contact compression, preformed rods distribute clamping force evenly across the entire winding length; this ensures strong grip while preventing localized damage to the conductor.
II. Friction Enhancement via the Inner Surface of the Rods
To further boost friction, the inner surface of the preformed rods is typically coated with a layer of high-strength emery or white fused alumina grit. Under the pressure of the helical winding, these fine particles create a microscopic "interlocking" effect with the conductor surface, significantly increasing the static coefficient of friction. Research shows that this design allows the grip to achieve over 95% of the conductor's rated tensile strength, with high-quality products sometimes exceeding 100%.
III. Graded Gripping via Multi-layer Structure
For long-span or high-tension lines, double-dead-end grips often utilize a multi-layer structure consisting of inner and outer layers of preformed rods. An inner layer of protective rods is first wrapped around the conductor to provide protection and initial fixation; an outer layer of dead-end rods is then wound over them, further increasing the total contact area and gripping force. The two sets of rods are connected and balanced via a triangular link plate, ensuring even load distribution and shared load-bearing.
Summary
The gripping force of a preformed double-dead-end grip relies fundamentally on the mechanical advantages of helical geometry, the friction-enhancing properties of the coating materials, and the cumulative effect of the multi-layer structure. This design not only ensures a strong and reliable grip but, more importantly, distributes stress evenly, fundamentally eliminating the risk of conductor damage caused by stress concentration-a common issue with traditional clamps.