Highlights & Key Sections
Bitumen in Cable Manufacturing
Bitumen in cable manufacturing stabilizes, seals, and protects: it impregnates jute or hessian servings on legacy PILC cables, forms anti-corrosion layers over lead sheaths, and fills/encapsulates low-voltage joints to block moisture and extend service life. Proper grade selection (e.g., oxidized 85/25–115/15) and controlled application are critical for durability, thermal behavior, and safety.
What exactly is bitumen in cable manufacturing—and where is it used today?
Bitumen is a hydrocarbon binder engineered (often by air-blowing/oxidation) to deliver a defined softening point and penetration. In cabling, it appears in three practical roles:
Outer serving impregnant on paper-insulated, lead-covered (PILC) cables to stiffen jute/hessian and repel water. Field guides document a bitumen layer covering lead on PILC constructions. See bitumen layer covering lead.
Anti-corrosion jacket over metallic sheaths (lead/steel) as a primary water barrier on older assets. Modern utility reviews confirm PILC remains widely installed, so these layers still matter in asset management; see the PILC environmental review.
Jointing and box filling compound for LV/MV accessories: hot-poured bitumen compounds encapsulate splices, exclude moisture, and distribute thermal stresses; this use is codified in the IS 1255 installation code.
Quick check — Is this still relevant if we use XLPE today?
Yes. Even where new builds are polymeric, utilities operate large PILC fleets, and joint bays/enclosures still employ bituminous systems for legacy interfaces and repairs. restservice.epri.com
Which types of bitumen are used in cable applications?
Core families you’ll encounter:
Oxidized (blown) bitumen — controlled air oxidation lifts softening point and lowers penetration for heat resistance and creep control (e.g., 85/25, 90/15, 115/15). Used for serving impregnation and cable/joint filling where a firm set is needed.
Penetration grades — softer binders occasionally blended when lower pour temperatures or flexibility are required.
Modified binders — select compounds incorporate inert fillers or waxes for drip resistance, dielectric strength, and tailored viscosity (specified via standards tests).
Standards snapshot: Formulations and tests for bitumen-based filling compounds for electrical purposes are specified in IS 7084, including penetration, softening point, electrical strength, and segregation tests. law.resource.org
Quick check — What do 85/25 or 115/15 mean?
They denote the approximate softening point (°C) / penetration (0.1 mm) pair—for example, 85/25 ≈ 85 °C softening point and 25 dmm penetration—signaling heat resistance and firmness.
Where does bitumen deliver the most value inside a cable system?
1) PILC outer serving and sheath protection
Impregnated jute/hessian resists water and abrasion.
Bitumen layers over lead minimize corrosion initiation points and seal microcracks at sheath/serving interfaces. Documented PILC constructions show an asphalt/bitumen layer even where jute is absent. digital-library.theiet.org
2) Joints, terminations, and boxes
Hot-poured, bituminous encapsulation reduces partial discharge risk from voids and blocks water ingression in straight-through and branch joints. IS 1255 provides typical drawings and allows bitumen-based filling compounds for PVC cable joints under stated precautions. law.resource.org
3) Ancillary sealing & bedding
In low-voltage accessories and legacy terminations, bitumen acts as a bedding/sealant to spread thermal stresses and prevent condensation.
Quick check — Is petroleum jelly the same as bitumen here?
No. Flooding/filling jellies (petrolatum/gel) are common in telecom/FOC for water blocking; bitumen is stiffer, higher-softening, and used where a firmer, semi-structural encapsulation or anti-corrosion layer is required.
How do you pick the right grade for a cable or joint?
Use conditions drive grade:
Thermal envelope: Select higher softening point (e.g., 95/25–115/15) for hotter enclosures or sun-loaded boxes; mid-range (85/25–90/15) for typical LV joint bays.
Installation method: Narrow ducts or congested joint bays favor grades with manageable pour viscosity (verify ring-and-ball softening and needle penetration).
Dielectric & integrity tests: Conform to IS 7084 proof tests (electric strength, segregation), plus site acceptance checks. law.resource.org
Quick check — One grade for all climates?
No. Match softening point to ambient extremes and load-related heating; using an overly soft compound risks drip/voiding, while too hard can stress insulation during cooling.
What are the safety and performance considerations?
Fire behavior: Bitumen-impregnated outer servings have known flammability potential; keep clearances, avoid excessive torching, and consider sleeves/over-jackets where mandated. EACorp Site
Environmental context: PILC lead sheaths with bitumen over-layers are under review in some jurisdictions; current U.S. assessments indicate low risk and no blanket removal requirement, but monitoring and compliant handling are advised. restservice.epri.com
Aging/maintenance: Inspect for cracking, embrittlement, or loss of adhesion at terminations; re-seal as needed.
Compatibility: Confirm adhesion to lead, tinned copper, steel armour, and legacy papers; avoid plasticizer migration into modern polymer components.
Quick check — Can I pour hot bitumen over polymeric insulation?
Only per accessory design and code. IS 1255 allows bitumen compounds with PVC cables with precautions; otherwise use the accessory system specified by the manufacturer. law.resource.org
How is bitumen applied and controlled during production and maintenance?
Production / refurbishment steps (typical):
Heat compound to controlled pour temperature (per grade’s softening point + manufacturer margin).
Dry the enclosure/box; pre-warm metallic parts to reduce chill and voids.
Pour & degas slowly to wet conductors/splices; tap for bubble release.
Cool under cover, avoiding rapid drafts; verify fill, re-top if needed.
Seal with compatible tapes/over-jacket.
Quality control checkpoints:
Penetration (ASTM D5), softening point (D36), electrical strength, segregation—as referenced in IS 7084. law.resource.org
Quick check — Where do suppliers position “electrical applications” of oxidized bitumen?
Producers list cable insulation and joint protection among established uses for oxidized grades; see electrical applications.
How does bitumen compare with modern alternatives?
Versus polymer gels/compounds: Gels provide re-enterability and low-temperature flexibility; bitumen offers higher softening points and a firmer mechanical encapsulation where re-entry isn’t needed.
Versus thermoplastic jackets: Modern PE/PVC/LSZH sheaths replaced bituminous servings on new builds; however, legacy networks still gain from bitumen’s moisture barrier and corrosion protection at the sheath/serving level. eatechnology.com+1
Quick check — Is bitumen “obsolete”?
No. It’s specialized: essential for legacy PILC protection and many LV jointing practices, while new lines rely on polymers.
What do recent field trends mean for my specification?
Life-extension of PILC: Utilities prioritize condition-based replacement and sealing remediation rather than wholesale removal; see the PILC environmental review.
Fire safety upgrades: Where bitumen-impregnated coverings remain, operators add fire-reactive wraps or over-jackets in high-risk spaces. EACorp Site
Documentation discipline: Reference IS 7084 for compound properties and IS 1255 for the jointing methods permitted in your jurisdiction. law.resource.org+1
Practical selection table
| Application area | Bitumen role | Why used | Typical grade families* | Key reference |
|---|---|---|---|---|
| PILC outer serving / sheath | Impregnation; anti-corrosion layer | Moisture barrier; abrasion resistance; corrosion control | Oxidized 85/25–95/25 | bitumen layer covering lead; PILC environmental review |
| LV straight-through joint | Hot-poured filling compound | Void-free encapsulation; moisture block | Oxidized 85/25–90/15 | IS 1255 installation code |
| Branch box / termination | Bedding & stress relief | Thermal distribution; sealing | Oxidized 90/15–115/15 | IS 7084 |
*Grades indicate softening/penetration families; verify exact specification and tests per standard and supplier datasheet. law.resource.org
Executive checklist (ready to use)
Identify cable family (PILC vs polymeric) and accessory design.
Select grade by temperature & geometry (start with 85/25–90/15 for LV joints; 95/25–115/15 for hotter bays).
Require IS 7084 property compliance and IS 1255 method conformity in the spec.
Define pour temperature, pre-warm, venting, and cooling protocol in work instructions.
Inspect historic servings; where present, retain/renew bitumen anti-corrosion layers.
Document re-entry policy (bitumen ≠ re-enterable), fire precautions, and environmental handling.
Where appropriate, leverage oxidized bitumen offerings designated for electrical applications and request certificates of analysis for each batch.
Final Q&A
What softening point should I target for an outdoor LV joint box in a hot climate?
Typically a higher softening point family (≈95/25 or 115/15) to resist drip in sun-heated enclosures; confirm by load profile and enclosure temperature mapping.Does bitumen improve dielectric strength inside joints?
Yes—when poured void-free it displaces air, reducing partial discharge inception; standards include proof/electrical strength checks to validate the compound.Can I reuse old bitumen from a joint during refurbishment?
No. Aged material may have oxidized, cracked, or absorbed contaminants. Remove, clean, and refill with fresh, tested compound.Is there any compliance difference between penetration and oxidized grades?
Oxidized grades are favored for higher softening points and dimensional stability; compliance is via the same family of penetration/softening/electrical tests.How does bitumen behave under short-term overloads?
Temperature rises soften the mass; selecting an adequate softening point and ensuring complete fill prevents voiding during cool-down.What’s the typical pour temperature margin?
Operationally set above the softening point to achieve flow without thermal damage to insulation; follow supplier limits and on-site thermometer checks.Does bitumen bond to lead sheaths?
Yes, provided surfaces are clean/dry and warmed; this contributes to corrosion protection on PILC constructions.Is bitumen acceptable in polymeric cable joints?
Only where the accessory design and local code permit; some LV PVC joints explicitly allow bitumen compounds with precautions.How do I audit workmanship on bituminous joints?
Check fill level/voids, surface wetting of conductors, absence of cracks after cool-down, and batch records (penetration/softening results).When should I choose a re-enterable gel instead?
Use gels when frequent maintenance/re-entry is required. Choose bitumen where permanent, rigid encapsulation and higher softening point are priorities.
Sources
IS 7084:1973 — “Bitumen based filling compounds for electrical purposes.” https://law.resource.org/pub/in/bis/S05/is.7084.1973.pdf
IS 1255:1983 — “Code of practice for installation and maintenance of power cables up to and including 33 kV.” https://law.resource.org/pub/in/bis/S05/is.1255.1983.pdf
EA Technology — “Cable Data Collector (CDC) Application Guide,” 2014. Anti-corrosion: Bitumen layer covering lead. https://eatechnology.com/media/ieoharej/cdc-application-guide-usa-r3.pdf
EPRI — “Environmental Impacts of Lead from Paper-Insulated Lead-Covered (PILC) Cable,” 2025. https://restservice.epri.com/publicdownload/000000000001009513/0/Product
PetroNaft — “Oxidized Bitumen (Blown Asphalt): electrical applications noted.” https://www.petronaftco.com/oxidized-bitumen/
Prepared by the PetroNaft Co. research team.