Stress Control Mastic
Semiconductive stress control mastic designed to regulate electrical field distribution at insulation screen cut-back points in medium-voltage cable joints and terminations — preventing stress concentrations that lead to partial discharge and premature insulation failure.
Field Grading at Medium-Voltage Cable Screen Transitions
When a medium-voltage cable's insulation screen is cut back during joint or termination preparation, the abrupt screen edge concentrates the electric field — initiating partial discharge and accelerating insulation degradation if left unmanaged. Stress Control Mastic is hand-applied at this transition to redistribute the field gradually across the cut-back zone, eliminating the stress peak.
Its controlled semiconductive resistivity forms a resistive grading layer between the screen edge and the insulation surface. Applied by hand-wrapping without heat, it fills voids and conforms to irregular geometries at connectors, lug interfaces, and screen steps.
- Material Semiconductive elastomer mastic
- Colour Yellow (standard)
- Voltage medium-voltage up to 36 kV
- Application Hand-wrapped — no heat required
- Form Roll — self-amalgamating strip
- Function Electric field grading
- Systems medium-voltage cable joints & terminations
Why Stress Control Mastic Is Specified
Directly addresses the primary electrical failure mechanism at medium-voltage cable screen transitions — with no specialist tooling and no heat required.
Electrical Stress Redistribution
Controlled semiconductive resistivity redistributes the electric field at the insulation screen cut-back — converting a sharp stress peak into a gradual, graded transition that the cable insulation can sustain reliably throughout the service life.
Partial Discharge Prevention
By eliminating the concentrated stress peak at the screen edge, Stress Control Mastic suppresses the initiation of partial discharge in the adjacent cable insulation — the principal cause of long-term insulation degradation in ungraded medium-voltage cable accessories.
Void Filling and Geometry Compensation
Flows under hand pressure to fill the voids and irregular profiles at screen edges, connector shoulders, and lug interfaces — eliminating air-filled cavities where partial discharge activity is initiated under medium-voltage electrical stress.
Stable Long-Term Performance
Maintains consistent semiconductive resistivity across the operating temperature range throughout the service life of the cable accessory — providing reliable stress grading under thermal cycling, load variation, and long-term field conditions.
Compatible with Heat Shrink Systems
Engineered for use within Western Cablex and standard medium-voltage heat shrink jointing and termination systems — the mastic and heat shrink components are thermally and chemically compatible across the installation temperature range.
No Heat or Specialist Tools Required
Hand-applied by wrapping and moulding — no hot air gun, resin mixing, or calibrated tooling required. Achievable under standard field jointing conditions by trained technicians following the joint instruction documentation.
Material & Performance Data
Reference data for engineering and procurement. Contact our technical team for volume resistivity data, compatibility confirmation, or project-specific qualification requirements.
| Base material | Semiconductive elastomer mastic — controlled volume resistivity |
|---|---|
| Colour | Yellow (standard) — distinguishes Stress Control Mastic from Black Mastic on site |
| Form factor | Roll — self-amalgamating strip; wraps and melds under hand pressure |
| Voltage application | Medium-voltage cable accessories — up to 36 kV system voltage |
| Electrical function | Resistive stress grading — redistribution of electric field at insulation screen cut-back |
| Application method | Hand-applied — wrap and mould; no heat source required |
| Operating temperature | –55°C to +90°C (continuous service) |
| Compatible systems | medium-voltage heat shrink jointing kits, medium-voltage heat shrink termination kits, cold-applied medium-voltage accessories |
| Cable insulation types | cross-linked polyethylene, ethylene propylene rubber — standard medium-voltage power cable constructions |
Where Stress Control Mastic Is Used
Applied at specific stress concentration points in medium-voltage cable joint and termination assemblies wherever insulation screen management is required.
medium-voltage Joint Screen Cut-back Zones
Primary application — applied at the insulation screen cut-back on each cable end within an medium-voltage straight or branch joint to grade the electric field at the abrupt screen termination before the heat shrink insulation system is applied over the joint.
medium-voltage Termination Screen Step Relief
Applied at the insulation screen cut-back during medium-voltage cable termination preparation — grading the stress at the screen edge before the stress control tube or termination body is installed over the prepared cable end.
Connector and Lug Interfaces
Applied around connector shoulders and lug body transitions to fill the void created by the irregular geometry between the conductor lug and the cable insulation — eliminating a common site for stress concentration and void-induced partial discharge.
Heat Shrink Termination Systems
Integrated as a standard step in Western Cablex medium-voltage heat shrink termination assembly — applied before the stress control tube is recovered over the prepared cable end, forming the initial grading layer in the termination's electrical design.
Distribution Substation Cable Preparation
Used in outdoor and indoor substation medium-voltage cable terminations — where reliable long-term electrical performance at screen transitions is critical to substation asset availability and maintenance schedules.
Industrial medium-voltage Cable Jointing
Applied in industrial facility medium-voltage cable joints and terminations — motor connections, switchgear cable entries, and transformer connections where medium-voltage cross-linked polyethylene or ethylene propylene rubber cable preparation requires screen stress management as part of the jointing assembly.
When and How to Use Stress Control Mastic
Stress Control Mastic is a step-specific component in medium-voltage cable accessory assembly. Confirm each parameter before use to ensure correct application at the right stage of the installation sequence.
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01
Confirm the System is medium-voltage
Stress Control Mastic is required for medium-voltage cable systems — typically 6 kV and above — where the electric field strength at the insulation screen cut-back is sufficient to initiate partial discharge without grading. For low-voltage systems (up to 1 kV), electrical stress grading is not required — use Black Mastic for void filling and sealing at low-voltage connector and joint interfaces. Stress Control Mastic is not a substitute for Black Mastic in low-voltage applications and vice versa.
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02
Identify the Application Point
Stress Control Mastic is applied at specific locations in the cable accessory assembly — not over the general cable surface. The primary application points are: the insulation screen cut-back edge on each cable end, the connector shoulder and lug-to-insulation transition, and any geometric step in the assembly profile that could concentrate electrical stress. Follow the installation instruction supplied with the joint or termination kit for the precise application sequence and dimensions.
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03
Cable Insulation Type
Stress Control Mastic is compatible with cross-linked polyethylene and ethylene propylene rubber insulated medium-voltage cables — the standard insulation types used in modern medium-voltage power cable constructions. Confirm the cable insulation type from the cable data sheet before ordering. For Paper Insulated Lead Covered cables, different stress control and sealing requirements apply — contact our technical team for the appropriate mastic specification for Paper Insulated Lead Covered cable jointing systems.
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04
Stress Control Mastic vs Anti-Tracking Mastic vs Black Mastic — Selecting the Correct Mastic
Three mastic formulations are available — each for a distinct function. Use Stress Control Mastic exclusively for electrical stress grading at screen transitions in medium-voltage systems. Use Anti-Tracking Mastic for surface tracking protection on outdoor medium-voltage termination bodies and exposed interfaces. Use Black Mastic for general void filling, moisture sealing, and connector interface protection across low-voltage and medium-voltage applications. Do not substitute one formulation for another — the electrical properties of each are formulated for a specific function.
Stress Control Mastic quantity per installation is determined by the cable insulation screen diameter and the length of the grading zone required by the joint or termination kit instructions. Contact our technical team if installation instructions for the specific kit are unavailable.
Common Technical Questions
In a medium-voltage cable, the electric field is radially distributed around the conductor and is contained by the conductive insulation screen. When the screen is cut back during jointing or termination preparation, the abrupt end of the screen creates a point where the electric field is forced to transition from inside the screen to outside it. This creates a concentrated stress peak at the screen edge — a localised area of high electric field strength that the cable insulation material was not designed to withstand at that point. Without stress control, this concentration initiates partial discharge activity that progressively erodes the insulation over time, ultimately leading to insulation failure. Stress Control Mastic provides a resistive grading layer that smooths the field transition over a defined length, eliminating the concentration and preventing the initiation of partial discharge.
In a standard heat shrink medium-voltage termination, Stress Control Mastic is applied at two locations: first, at the insulation screen cut-back edge — wrapping the mastic around the screen end and extending it a defined distance onto the cable insulation surface to form the resistive grading ramp; and second, around the connector or lug body transition — filling the void between the lug shoulder and the cable insulation surface. The exact dimensions and application sequence are specified in the jointing kit installation instructions. Follow these instructions precisely — the grading zone length and mastic build-up thickness are critical to the electrical performance of the completed termination.
The three mastics are formulated for distinct functions and are not interchangeable. Stress Control Mastic — yellow — is semiconductive and is used exclusively for electric field grading at screen transitions in medium-voltage systems. Anti-Tracking Mastic is formulated to resist surface tracking on outdoor medium-voltage termination bodies and exposed insulation surfaces under combined electrical stress and pollution. Black Mastic is a general-purpose sealing and void-filling compound used for moisture protection and connector interface filling in low-voltage and medium-voltage applications. Using Black Mastic in place of Stress Control Mastic at a screen cut-back will not provide stress grading — Black Mastic has insulating (not semiconductive) properties and will not redistribute the electric field.
Stress Control Mastic is applied by unwinding a length from the roll and wrapping it around the cable at the screen cut-back position. It should be applied in overlapping half-lapped turns, building up the profile to the dimensions specified in the kit installation instructions. After wrapping, mould the mastic firmly by hand to consolidate the layers, eliminate air pockets, and conform the mastic to the cable surface profile. The cable surface must be clean and dry before application — contamination at the interface reduces the effectiveness of the stress grading layer. No heat is required; the mastic self-amalgamates under hand pressure.
Yes. Stress Control Mastic is compatible with both cross-linked polyethylene and ethylene propylene rubber insulated medium-voltage cables — the two principal insulation types used in modern medium-voltage power cable constructions. The mastic adheres to both insulation surfaces under hand moulding and provides the required semiconductive grading layer in either case. For older cable constructions including Paper Insulated Lead Covered or paper-insulated cables, confirm the appropriate mastic specification with our technical team before use, as the jointing system requirements differ from those for extruded insulation cables.
Stress Control Mastic should always be applied following the installation instructions for the jointing or termination kit being used. The stress grading design of an medium-voltage cable accessory system — including the grading zone length, mastic build-up profile, and relative position of the Stress Control Mastic layer within the overall accessory assembly — is part of the electrical design of the complete system. Applying Stress Control Mastic without reference to the specific kit instructions risks incorrect grading zone dimensions, which may result in insufficient stress control or incompatibility with the heat shrink or cold-applied components installed over it. Contact our technical team if kit instructions are not available for the cable and accessory type being used.
Need Help Specifying the Right Mastic for Your Application?
Speak with our technical team for formulation guidance, system compatibility confirmation, and supply enquiries.