Wire and cable can sometimes be confusing, especially when discussing insulation materials.
One insulation type is cross-linked polyethylene (XLPE), which can be based on either low-density polyethylene (LDPE) or high-density polyethylene (HDPE) and is used to insulate conductors. XLPE uses a grafted polymer combined with a catalyst to speed up the crosslinking reaction and provide other properties. Several different catalysts can be used with the same graft, depending on the application or specification.
Unlike thermoplastic materials that can be reheated and remolded without changing their chemical makeup, you only get one chance with thermosets. This is because materials like XLPE change and become stronger during the post-extrusion curing process.
In even simpler terms, thermosets feature crosslinked chains while thermoplastics don’t.
When the crosslinking reaction occurs, like those in XLPE wires, it changes the physical properties of the plastic. Crosslinking occurs after the material has been extruded onto the conductor and begins to cure, building links between chains. Curing (hardening) is accelerated by exposure to heat and moisture.
The result is an XLPE insulated cable with high tensile strength and other benefits.
The cross-linking process does more than make the cable stronger – it fundamentally changes its makeup to produce a remarkably impressive insulation.
Because of this super-strong insulation, cross-linked polyethylene has become a common choice across many industries, including power transmission, industrial applications like power, lighting control and signaling, oil and gas, and aerospace use.
Crosslinking reactions change the polymer’s molecular weight, making XLPE insulation more rigid and durable. This makes it excellent for underground or underwater applications and where stress is expected. The stronger bonding in the plastic also lends itself to several other improvements.
Stronger insulation means the cable offers better protection during installation and holds up better in harsh environments or varying temperatures. The wire is also better equipped to withstand long-term use by reducing environmental stress cracking.
Higher stress tolerance means the cable can be manipulated more without showing signs of damage. This means conductors can stretch, have better physical strength, and absorb crushing better than other insulation types.
Stress resistance also applies to electrical stress, which happens when voltage flowing through the conductor creates hot spots in the wire. If enough damage occurs in these spots, the cable could eventually fail. XLPE insulation helps distribute electrical stress more evenly, preventing hot spots from forming and extending the wire’s lifespan.
LDPE and HDPE are already good at resisting oil and gas damage, but crosslinking them boosts those properties even more, including at higher temperatures. As a result, crosslinked polyethylene can be used in harsher environments.
Once crosslinked, XLPE does not melt, so it excels in areas where the temperatures can get hot. Insulated conductors can withstand operating temperatures up to 120°C and even above 150°C in some cases without suffering damage.
The insulation also protects other nearby wires and cables from heat generated by electrical currents traveling through a copper wire.
One major piece of the XLPE production process is adding a catalyst to help facilitate cross-linking. By adding different catalyst compounds to the polymer mix, the insulation can take on other properties like sunlight resistance, flame retardance, and anti-oxidation characteristics that increase the usable lifespan of the wire.
XLPE is also available in a low-smoke, zero-halogen (LSZH) product if it’s used with a halogen-free flame-retardant material. The wire’s characteristics depend on the catalyst masterbatch used and what properties the wire needs.
You can typically find XLPE used as insulation on low-, medium-, and high-voltage cables across many industries. At Kris-Tech, we use XLPE insulation for several products, including:
The insulation is also commonly used for medium voltage applications ranging from 2-5kV or made into a halogen-free product for use in office spaces, closed areas, mass transit, and other high-traffic locations.
No matter the industry, you’re likely to find XLPE insulation used in some form – sometimes not even as insulation. For example, PEX (polyethylene–crosslinked) tubing has been a popular alternative for copper and Polyvinyl Chloride (PVC) tubing in plumbing applications for decades, thanks to its durability and ability to withstand stress.
Next time you need wire insulation capable of surviving nearly anything thrown at it, think of XLPE and install it confidently!
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