ADSS Electrical Tracking: Why It Happens and How to Prevent It

ADSS cable electrical tracking — often called electric corrosion in Chinese utility practice — is sheath erosion caused by dry-band arcing on a contaminated, wetted cable surface. It is not a random material failure. It happens when an all-dielectric cable is installed at a tower position where the surface electric field, pollution level and moisture combine beyond what the sheath was designed to withstand.

The practical consequence is severe: the polyethylene or AT sheath erodes in small arcs over months or years, water reaches the strength members and fiber, attenuation rises, and in the worst case the cable breaks over a span. Because the damage starts on the outside and progresses slowly, it is usually invisible until a failure or an inspection campaign finds it.

This guide explains the mechanism, the factors that decide risk, how to select ADSS cable for high-field routes, what to check during installation, and how to detect tracking before the fiber fails.

What electrical tracking actually is

ADSS cable is all-dielectric: it has no metal armor, no messenger wire and no metallic shield. That is exactly why it can be installed on high-voltage towers without a grounded path. But “no metal” does not mean “no electrical stress”. The cable sits in the electric field of the phase conductors and reaches a floating potential through capacitive coupling.

In dry, clean conditions the sheath is an insulator and almost no current flows. Once the surface is coated with dust, salt, agricultural chemicals or industrial pollution and then wetted by fog, dew or rain, that contamination layer becomes slightly conductive. A leakage current flows along the sheath to the fittings and the tower. The current heats the surface, dries a narrow band, interrupts the current, and the voltage re-establishes across that dry band as a small arc. Repeated arcs carbonize and erode the sheath. This is dry-band arcing, and the resulting damage is tracking and erosion.

The failure sequence in five steps

1. Contamination builds up on the sheath — salt in coastal areas, dust and sand in arid regions, ash and chemicals near industry.
2. Wetting from fog, rain or condensation turns the contamination into a conductive film.
3. Leakage current flows along the surface toward the grounded hardware.
4. Dry-band formation interrupts the current and creates a small arc across the dried section.
5. Sheath erosion repeats at the same locations until the sheath is penetrated and moisture reaches the cable core.

Tracking should not be confused with three other problems that look similar from a distance: corona discharge at hardware, a one-off flashover, and ordinary UV or mechanical aging. Tracking leaves a characteristic pattern of erosion grooves, chalky residue and pinholes, usually concentrated near the attachment points where the field is highest.

Why ADSS is more exposed than OPGW

OPGW combines the communication function with a grounded earth wire. Its metallic armor is bonded to the tower, so the electric field across the outer surface is controlled by the grounding system. ADSS has no such path: the sheath itself must withstand the surface field. That is the trade-off for easy installation on existing towers, and it is why ADSS selection is fundamentally an electric-field design task, not only a mechanical one.

This is also why two projects with the same fiber count, the same span and the same price can have completely different service lives. The cable structure may look identical on a datasheet, while the sheath compound, the attachment position and the calculated surface field are not.

Six factors that decide whether tracking will occur

How to select ADSS cable for high-field routes

1. Calculate the surface field, tower by tower

Do not use an “average” field value for a whole line. The field changes with phase arrangement, tower type, attachment height, span and sag. The critical points are usually the suspension and dead-end positions closest to the phase conductors. A route can be low-risk for 80% of its towers and high-risk at a handful of them; those few towers will determine the failure history of the whole line.

As a screening reference, many utilities design tracking-resistant ADSS for a maximum surface field of roughly 12 kV/m at the attachment point. This is a screening value rather than a universal rule: the acceptable limit depends on the sheath compound, the pollution class and the utility’s own standard. Confirm it against the test data for the specific cable and against the applicable specification. Standard PE sheath should not be used where the calculated field and pollution level call for AT.

2. Keep everyday stress inside the design envelope

Mechanical and electrical risk interact. An over-tensioned cable has less margin, may creep and change position, and is less tolerant of hardware movement. Keep the everyday stress (EDS) within the design limit — commonly around 20–25% of rated tensile strength, depending on the utility standard — and check the maximum tension and sag for the actual span rather than the nominal one.

3. Specify the sheath by function, not by color

“Black PE” is not the same as “tracking-resistant sheath”. AT compounds are formulated to resist tracking and erosion under wet, contaminated conditions. Ask for the compound type, the supplier’s tracking and erosion test report, and evidence of long-term outdoor performance. If the route crosses coastal salt fog, industrial pollution or dry, dusty regions with heavy dew, this is not a place to save a few percent on the sheath.

4. Match the fittings to the cable and the load

Use suspension and dead-end sets rated for the cable diameter and the calculated load. Armor rods, helical suspension sets and vibration dampers must be compatible with the sheath; a poor fit concentrates pressure and can start mechanical damage that later becomes a tracking site. For long spans, check the hardware’s slip and creep behavior, not only its breaking load.

5. Check the whole route, not just the cable

Tracking risk also depends on nearby insulators, contamination sources and maintenance practice. A cable routed close to heavily polluted insulators or in a coastal corridor with frequent fog will see more wetting and more contamination. Where possible, choose a tower position that reduces both field and contamination, even if it requires a slightly longer jumper or a different bracket.

Installation details that make a real difference

• Protect the sheath during pulling. Use rollers and pay-off equipment that do not drag the cable over concrete, steel edges or rough ground. A deep scratch is a future tracking initiation point.
• Control sag and tension. Install to the calculated stringing table; do not adjust sag by feel. Recheck after the line has been energized and after the first seasonal temperature cycle.
• Keep clamps clean and correctly torqued. Grit trapped under a clamp can abrade the sheath. Follow the fitting supplier’s torque and interface requirements.
• Avoid unnecessary contact. Cable should not rub against tower members, insulators or other cables under wind-induced movement.
• Record the as-built position. Document the attachment point at each tower. If a tracking problem appears later, this record is what allows a meaningful field review.

Inspection: catching tracking before the fiber breaks

Tracking is a surface phenomenon before it becomes an optical problem, which gives inspectors a window of months or years. A practical inspection program combines visual checks with optical trend data.

Optical testing that supports the diagnosis

Use OTDR traces from both ends and compare them with the as-built baseline. A localized loss increase at a splice or at a point near an attachment is a strong hint of moisture ingress. Attenuation measured at both 1310 nm and 1550 nm helps distinguish a mechanical bend from contamination-related loss. Record the trend: a single measurement tells you little, but three measurements over a year tell you whether the cable is degrading.

Repair and mitigation options

• Replace the damaged section. Cut out the eroded span, install a repair length and use a properly sealed splice closure. Do not simply wrap the damaged sheath and return the line to service.
• Move the attachment point. If the failure is concentrated at one tower type, recalculate the field and relocate the cable to a lower-field position where the design allows.
• Upgrade the sheath specification. For replacement cable, specify an AT sheath and request the tracking and erosion test report.
• Reduce mechanical stress. Review span, sag and fitting compatibility; a cable that moves at the clamp erodes faster.
• Clean and monitor. In polluted or coastal areas, periodic cleaning reduces the conductive layer. It is a maintenance measure, not a substitute for correct selection.

Frequently asked questions

Does ADSS cable carry electrical current?

It has no metallic conductor for power, but its surface can carry a small leakage current when contaminated and wet. That leakage current is what creates dry-band arcing and tracking.

Can standard PE sheath be used on 110 kV or 220 kV lines?

Only where the calculated surface field and pollution level are low enough for that sheath. On high-field or polluted routes, specify a tracking-resistant (AT) sheath and verify the design with the cable supplier and the utility’s standard.

What surface field is acceptable for ADSS?

There is no single universal number. Many utilities use a screening limit of about 12 kV/m for tracking-resistant sheath, with lower limits for standard PE. The correct value depends on the sheath compound, pollution class, wetting regime and the applicable standard — always confirm with test data and the project specification.

Why does the cable fail after several years if it passed factory tests?

Factory tests verify the cable at the time of delivery. Tracking is a long-term interaction between surface contamination, moisture and electric field. A cable can pass every factory test and still fail in service if it is installed at a tower position where the field exceeds what its sheath can tolerate.

How can tracking be detected early?

Combine visual inspection near fittings, infrared/UV/ultrasonic detection where available, and a trend of OTDR and attenuation measurements. Early signs are surface discoloration, chalky residue and small erosion marks rather than a sudden optical failure.

Is OPGW always the better choice?

OPGW avoids the tracking mechanism because its metallic armor is grounded, and it provides a earth wire function. But it requires a ground-wire replacement and a different installation scope. ADSS remains attractive for retrofitting communication onto existing towers when the field and sheath are correctly engineered.

Send your route data for an ADSS selection review

If you are selecting ADSS for a high-voltage route, the useful starting point is not a fiber count — it is the electrical and mechanical environment. Send us the system voltage, tower type and attachment points, span and sag, pollution or coastal exposure, ice and wind loads, required fiber count and the utility standard you are working to. Our engineering team can help match the sheath, span and fittings to the actual route.

Request an ADSS cable selection review or explore our ADSS fiber optic cable range.

Standards referenced in this article include IEEE 1222 (all-dielectric self-supporting fiber optic cable), IEC 60794 (optical cable test methods), IEC 60587 (tracking and erosion resistance under severe ambient conditions) and IEC 60815 (pollution dimensioning). Project-specific limits should always be confirmed against the utility specification and the cable supplier’s test data.