WB Tape: Two Paths

Assign radial and longitudinal moisture to correct layers. Water blocking tape in power cable construction is mainly a longitudinal defense: when moisture reaches an internal void, the swellable layer helps restrict its travel along the cable. A radial barrier has a different job—reducing entry through the cable circumference. Reliable designs assign both risks to the correct layers and validate the finished construction.

Why Water Blocking Tape in Power Cable Is Not a Radial Barrier

Radial and longitudinal describe directions, not interchangeable product names. Radial ingress crosses the outer sheath or another circumferential barrier, whether by permeation or damage. Longitudinal migration follows available paths along the conductor, screen wires, core interfaces or laid-up interstices. The IEC 60502-2 scope explicitly separates consideration of radial ingress risk from cable designs claimed to prevent longitudinal water penetration.

A polymeric sheath, bonded laminate or metallic sheath may form part of the specified radial protection. A swellable tape does not make a damaged sheath intact again. Water activates its absorbent component, which expands into nearby free volume and helps shorten the migration path. A complete design may therefore need both radial and longitudinal layers.

Review by moisture path, not by a single “water-blocked” label. Mark the sheath, radial barrier, conductor interstices, screen-wire region, core assembly and terminations, then assign a material and verification method to each required path.

Conceptual cutaway: radial entry control and longitudinal migration control are separate design functions.

Place the Tape Where Water Can Actually Travel

Placement starts with the cable cross-section. In a single-core screened power cable, axial channels can exist around the metallic screen and within a stranded conductor. In a multicore design, the laid-up interstices introduce additional free volume. The BASEC guide to MV distribution cables notes that swellable tapes may be used around a metallic screen and that the material under a metallic screen must not interrupt the required electrical connection.

For every proposed tape layer, record:

• the adjacent layers and whether electrical continuity is required;
• whether the tape is applied helically or longitudinally;
• finished width, thickness, overlap and applied tension targets;
• available expansion space after extrusion or assembly;
• maximum process exposure and compatibility with adjacent compounds; and
• the cable-level water-penetration requirement and test edition.

Conceptual comparison of circumferential entry and axial migration paths; exact construction varies by cable design.

Diameter alone does not set tape width; lay angle, overlap, tension, tolerances and line speed determine coverage. Even a tape that meets a laboratory swelling result can leave a channel if it wrinkles, necks down, gaps at a splice or lacks useful expansion space.

Choose Non-Conductive or Semi-Conductive Tape by Interface

Electrical function determines tape type. Where the layer must maintain contact across a screen system, the cable drawing may require a semi-conductive water-blocking grade with specified electrical properties. Where no conductive path is required, a non-conductive grade may be appropriate. The decision belongs to the approved cable design; color or visual similarity is not a substitute for resistivity data.

Chaowang CW-5 non-woven water blocking tape is publicly described as polyester non-woven fabric, superabsorbent resin and adhesive, with single- and double-sided grades. Its public page does not identify CW-5 as semi-conductive or publish an electrical-resistivity value. Do not place ordinary CW-5 at an interface that requires semi-conductivity unless a current approved datasheet explicitly supports that use. Chaowang lists a separate CW-8 semi-conductive water blocking tape family for review when that electrical function is required.

Also keep product roles separate. The CW-1 non-woven binding tape is intended for binding cable cores; it is not a swellable water-blocking substitute. Buyers comparing the broader non-woven cable tape range should identify the required function first—binding, electrical interface or water blocking—before comparing dimensions.

Conceptual layer-placement view; electrical interface requirements must come from the approved cable drawing.

Specify and Validate the Complete Moisture-Control System

A useful RFQ begins with the construction, not a generic request for “waterproof tape.” Send a marked cable drawing, voltage class, conductor and screen arrangement, adjacent materials, application method, nominal and tolerance dimensions, line conditions, target roll geometry and the governing finished-cable test. State whether the tape must be non-conductive or semi-conductive. If a conductivity requirement exists, include the measurement method and acceptance limits from the approved design.

Review the current datasheet and a representative sample before approval. Incoming checks may cover mass per unit area, thickness, tensile behavior, moisture content and swelling response under the agreed method. Run the tape on the intended equipment and inspect coverage, edges, splices, dust, telescoping and surface condition after processing.

Final acceptance must remain at cable level. IEC 60502-2 includes an associated test for designs claiming longitudinal water-penetration prevention, while project or regional specifications may define different samples, conditioning and pass criteria. Confirm the applicable edition rather than borrowing a convenient test from another cable family. Installation controls still matter: protect cable ends and prepare joints and terminations according to the approved procedure.

Frequently Asked Questions

Is water blocking tape the same as a radial moisture barrier? No. A swellable tape generally helps restrict water movement along internal cable paths after moisture reaches it. A radial barrier is part of the circumferential system intended to resist entry across the cable radius. Some cable designs use both, and neither term should be used as shorthand for the complete moisture-protection system.

Does water blocking tape prevent all water from entering a power cable? It should not be specified with that blannet promise. Entry can occur through a damaged sheath, an exposed cable end, a poor joint or another route. Tape performance depends on correct location, continuous coverage, available swelling space and compatibility. The finished cable must meet the water-penetration requirement chosen for its design and application.

When is a semi-conductive water blocking tape required? Use it when the approved electrical design requires the blocking layer to participate in or preserve a conductive interface, commonly around particular screen arrangements. The requirement should name an electrical property, method and limit. Do not infer semi-conductivity from a dark color, a product photo or the general phrase “water blocking tape.”

Where can CW-5 be placed in a cable? The public CW-5 page describes application on a cable conductor surface and outside an insulation layer, but the final position depends on the cable drawing and electrical interface. Confirm whether the chosen grade is single- or double-sided, whether a non-conductive layer is acceptable, and whether its dimensions and swelling behavior suit the available space.

Can a tape swelling result prove the completed cable is water blocked? No. A material test characterizes a specimen under stated conditions; it does not capture gaps, overlap variation, compression, conductor channels, splices or terminations in the finished cable. Use material data for screening and incoming control, then qualify the process and test the completed cable to the applicable project or product standard.

What information should a buyer send with a sample request? Provide the cable cross-section, tape position, adjacent layers, voltage class, conductive or non-conductive requirement, finished width and thickness, winding method, overlap, line speed, processing temperatures, roll dimensions and target cable-level test. If any value is unsettled, flag it for a joint review rather than asking the supplier to guess the design.

For a project-specific water blocking tape in power cable review, send Jiangsu Chaowang New Material the marked construction drawing, interface requirement, target tape dimensions, winding conditions and governing test. Start with the Chaowon cable-materials overview, then request the current CW-5 datasheet and a sample for line and finished-cable validation.