Cables and Cable Accessories in the Rainy Season: Challenges and Best Practices

The rainy season brings much-needed water to the environment, but for electrical power systems, it brings a host of challenges. Cables and their accessories—joints, terminations, and connectors—are particularly vulnerable during periods of heavy rain, high humidity, and flooding. Moisture is the enemy of electrical insulation, and the rainy season is when this enemy is most active. This article explores the specific challenges that wet weather poses to cables and accessories, and the best practices for ensuring reliable operation during and after the rains.

1. The Threat: Why Rain Is Dangerous for Power Systems

Rain and high humidity affect electrical systems in several ways:

• Water ingress – Water can penetrate cable jackets, joints, and terminations through damaged or poorly sealed areas.

• Reduced insulation resistance – Moisture on or within insulation creates leakage paths, reducing the effectiveness of the insulation.

• Partial discharge (PD) – Water ingress into voids or at interfaces can initiate PD, which erodes insulation over time.

• Corrosion – Water accelerates the corrosion of metallic conductors, connectors, shields, and armour.

• Flashover – On outdoor terminations, rain can bridge the creepage distance, causing surface flashovers.

• Flooding – Submersion of underground cables or equipment can lead to long-term degradation if not properly designed for water immersion.

The rainy season amplifies all of these risks, making it a critical period for inspection and maintenance.

2. How Rain Affects Different Cable Types

Not all cables are equally vulnerable to rain. Their construction determines their resilience.

For outdoor cables, the outer jacket is the first line of defence. If it is cracked, abraded, or degraded by UV, rain will find its way inside.

3. The Vulnerability of Cable Accessories

Cable accessories—joints, terminations, and connectors—are more vulnerable to rain than the cable itself. This is because:

• They have interfaces – The seal between the accessory and the cable jacket is a potential entry point.

• They are field-assembled – The quality of the seal depends on the installer's skill.

• They are often exposed – Outdoor terminations are directly exposed to rain.

• They contain multiple materials – Differential thermal expansion can open gaps over time.

Common rainy-season failures in accessories include:

• Moisture ingress at the cable jacket entry – If the sealing mastic is not applied correctly, water can creep along the interface.

• Water pooling inside joint casings – Poorly drained or unsealed joint boxes can fill with water, submerging the conductors.

• Flashover on outdoor terminations – Rain can create a continuous water film on the surface, causing a flashover.

• Corrosion of connectors – Water entering a termination can corrode the lug or connector, increasing resistance and generating heat.

• Partial discharge in wet voids – Water in a void creates a conductive path, lowering the PD inception voltage.

4. Flooding: The Ultimate Test

During severe storms, underground cable ducts, manholes, and vaults can flood. Cables that are not designed for continuous water immersion (i.e., those without water-blocking features) may suffer rapid degradation.

In flooded conditions:

• Conventional cables – Water can wick along the conductor or between the insulation and the jacket, causing widespread failure.

• Water-blocking cables – Swellable tapes and powders block water migration, limiting damage to a small section.

• Joints and terminations – Unless they are resin-filled or otherwise sealed, joints and terminations will fail when submerged.

Submarine and underground cables with special water-blocking construction are recommended for flood-prone areas. For existing installations, ensuring that manholes have proper drainage and that cables are not submerged is essential.

5. Electrical Consequences of Water Ingress

The electrical impact of water ingress can be immediate or delayed:

The delayed effects are particularly insidious. A cable may continue to operate for months or years after water ingress, only to fail suddenly.

6. Inspection and Maintenance During the Rainy Season

Regular inspection during the rainy season can catch problems before they cause failure.

Key inspection points:

• Outdoor terminations – Check for water stains, cracks, or tracking (carbonised paths) on the weather sheds. Ensure the cable entry seal is intact.

• Joints and manholes – Check for water accumulation inside joint boxes or manholes. Pump out if necessary.

• Cable jackets – Look for cracks, abrasion, or damage that could allow water ingress.

• Connections – Thermal imaging can detect hot spots caused by corrosion or loose connections.

Maintenance actions:

• Re-apply sealing mastic if it shows signs of degradation.

• Install additional weather sheds on outdoor terminations if needed.

• Improve drainage around underground joints and manholes.

• Apply hydrophobic (water-repellent) compounds to termination surfaces.

7. Installation Best Practices for Wet Conditions

If installation work must be done during the rainy season, extra precautions are needed:

• Work under cover – Use tents or temporary shelters to keep the work area dry.

• Dry the cable – If the cable has been exposed to rain, dry it thoroughly before installing accessories.

• Use cold-shrink accessories – Cold-shrink terminations are quicker to install and less sensitive to moisture than heat-shrink types.

• Check humidity – High humidity can cause condensation on cleaned surfaces. Use dehumidifiers if necessary.

• Seal promptly – Do not leave prepared cable ends exposed overnight; seal them with plastic bags or end caps.

8. Designing for Rain: What to Specify

For new installations in rainy or flood-prone areas, consider specifying:

• Water-blocking cables – With swellable tapes or powder.

• Fully sealed terminations – Cold-shrink or pre-molded types with robust seals.

• Resin-filled joints – These are completely waterproof and suitable for submersion.

• Outdoor terminations with long creepage distances – Extra weather sheds for heavy rainfall.

• Flood-proof manholes – With sump pumps and water-level alarms.

Specifying the right products from the start can save significant maintenance costs and outage risks later.

9. What to Do When a Cable Gets Soaked

If a cable is suspected of water ingress:

• Isolate and de-energize – Do not operate a cable with known water ingress.

• Test insulation resistance – A low reading confirms water ingress.

• Determine the extent – Use time-domain reflectometry (TDR) to locate the water entry point.

• Dry the cable – In some cases, cables can be dried by passing a low current through the conductor (for hours or days) or by using dry gas purging.

• Replace damaged sections – If drying is not possible, cut out and replace the affected section with a new joint.

Prevention is always better than cure. Regular inspection and prompt repair of damaged jackets or seals can prevent water ingress from becoming a major problem.

The rainy season is a demanding test for any electrical power system. Cables and accessories that are well-designed, properly installed, and regularly maintained will pass this test with ease. Those with weak seals, damaged jackets, or poor installation will fail—often spectacularly.

By understanding the threats that rain presents and taking proactive measures, utilities and industrial operators can ensure that their power systems remain reliable even during the wettest months. Rain is a natural part of the environment; it does not have to be a threat to the power supply.