Non-shrinkable tape
Building insulation by hand where nothing can be shrunk on
Every turn you lay can trap air, and air is the one defect nobody can see afterwards.
Air is what kills a hand-built wall. Not water, not heat, not the material.
A wall built turn by turn has a spiral seam running through every layer of it. Leave a pocket of air anywhere along that helix and you have put a void inside the dielectric. Dry air at sea level breaks down at roughly 3 kV per millimetre. The material around the void holds 42 kV per millimetre. So the void ionises long before the wall it sits in comes anywhere near its own limit.
That discharge then erodes the layer faces from the inside outwards. It runs for months. From outside the wrap looks as good on the day it fails as on the day it went on. The first evidence you get is the fault.
This is the whole argument for cold flow. The overlap discipline below matters more here than the material specification. Gala's non-shrinkable insulation tape is EPR-based. Wrapped half-lapped, its layers flow together under tension and bond into one body rather than a stack of separate turns. There is no shrink step to squeeze them for you, so the pressure has to come from your hands.
It belongs on a wraparound reference for the reason the wraparound sleeve does. Some shapes cannot be threaded and cannot be shrunk on. A branch, a shoulder at a lug, a tight bend. Where no moulded part and no tube fits, the wall gets built by hand or not at all.
The manufacturer's own listing is the non-shrinkable high voltage tape page, which publishes two roll sizes and six properties.
GNT 1 and GNT 2 non-shrinkable high voltage insulation tape
An EPR-based insulation tape wrapped half-lapped by hand, layer on layer, until the required build-up is reached. Cold flow bonds successive layers into a void-free body on XLPE, PVC, PILC and rubber-sheathed jackets. Manufactured by Gala Thermo Shrink Pvt. Ltd.
- Cold flow bonds layers applied at 50% overlap into a void-free build-up
- Resists moisture, contamination and adverse environmental conditions
- UV-stabilised and weather resistant
- High heat dissipation helps keep the conductor cooler
- Protects conductor material against corrosive elements in the environment
| Material | EPR-based, non-shrinkable |
|---|---|
| Application | Hand-wrapped, level-wound, half-lapped at 50% overlap |
| Thickness | 0.75 mm, both codes |
| GNT 1 roll | 25 mm minimum width, 9.1 m minimum length |
| GNT 2 roll | 50 mm minimum width, 10 m minimum length |
| Dielectric strength | 42 kV/mm |
| Jackets listed | XLPE, PVC, PILC and rubber-sheathed |
| Standard colour | Black |
| Storage life | At least five years, stored at +10 °C to +30 °C |
Physical properties
| Property | Test method | Nominal value |
|---|---|---|
| Tensile strength | BS 903 | 3 MPa |
| Elongation | BS 903 | 900% |
| Thickness | Not stated | 0.75 mm |
Nominal values as published by the manufacturer for the non-shrinkable insulation tape. The thickness row carries no test method on the source, and is printed here as it stands.
Electrical properties
| Property | Test method | Nominal value |
|---|---|---|
| Dielectric strength | ASTM D149 | 42 kV/mm |
| Dielectric loss angle | ASTM D149 | 0.005 |
| Volume resistance | ASTM D257 | 1 × 10¹³ ohm·m |
Dielectric strength is measured through the thickness of the material. It is not a rating for the wall you build out of it.
Two of these steps are the manufacturer's. Three are ours
Half-lapped level-wound wrapping at 50 percent overlap, carried on until the required build-up is reached, is the manufacturer's published method. Surface preparation, tension and how the wrap starts and finishes are this site's reconstruction from ordinary field practice. The product page covers none of them. If a jointing kit came with an instruction sheet, that sheet governs and this sequence does not.
How the build-up goes on
The tape does one job well and it does it only if the layers touch each other everywhere.
Clean back to sound, dry surface
Cold flow bonds the tape to itself. It cannot bond through grease, duct lubricant or a wet jacket. Take the preparation well past the damage on both sides so the first and last turns land on jacket that is still intact.
Half-lap every single turn
Each turn covers half the width of the one before it. On a 25 mm GNT 1 roll the wrap advances 12.5 mm per turn. On a 50 mm GNT 2 roll it advances 25 mm. Narrow tape follows a small radius or a shoulder far better; wide tape covers a straight length in half the turns.
Count the wall in passes, not in turns
The tape is 0.75 mm thick, so a half-lapped pass leaves two thicknesses behind it. One pass is 1.5 mm of wall. Four passes are 6 mm. That is arithmetic off the published thickness, not a published table. The wall your specification demands comes from the joint design, not from the roll.
Keep tension in the roll throughout
Pressure is what makes cold flow close the seam between layers. A slack turn leaves an air channel running the length of the helix. There is no recovery step here to pull the layers down, so every turn has to be laid tight as it goes on.
Finish on sound jacket, tail wrapped down
Bring the last pass the same distance beyond the damage as the first one started before it. Wrap the cut end down under a final turn instead of leaving it standing proud. A lifted tail is where water gets its first grip.
Not published — get these in writing
The manufacturer's page for this tape publishes six properties, two roll sizes and one storage range. It gives no voltage class, no operating temperature range for the tape in service, no track resistance result and no adhesion or peel figure. Note also that +10 °C to +30 °C is a storage condition. It is not a service temperature, and it must never be quoted as one. The PDF linked from that page, High-Voltage-Insulation-Sheet.pdf, is a scan carrying no extractable text. We cannot tell you what it adds. Open it yourself, and ask for any figure a specification will cite.
Where this is the wrong part
Hand build-up is slow and it is operator-dependent. Two crews wrapping the same joint do not produce the same wall.
- A geometry a kit already covers. Where a moulded part, a tube or a wraparound exists for that shape, use it. The kit part carries a size chart and a recovery check; a hand wrap carries whoever wrapped it.
- A busbar connection. A shrinkable tape recovers onto the bar and supplies its own tension. Start at heat shrink tape for bends a tube cannot be threaded onto before reaching for a hand build-up.
- Filling a step or a cavity. This tape spans; it does not fill. A shoulder at a lug or an armour cut needs mastic worked in underneath first, not more turns laid over the top.
- Damage that has reached the insulation or the screen. A wall is not a screen and it is not a stress cone. If the jacket alone is torn, that is a different repair entirely: see the wraparound cable repair sleeve.
- A specification that must name a kV class. 42 kV/mm describes the material through its thickness. Multiplying it by the wall you wrapped does not produce a voltage rating for the joint.
- Stock that has been sitting hot. Five years is the published life at +10 °C to +30 °C. A site container in an Indian summer is nowhere near that band, and the roll will not tell you how long it spent there. Date the stock as it comes in.
- A jacket outside the listed four. XLPE, PVC, PILC and rubber-sheathed are what the manufacturer states. Anything else needs confirming before it goes on.
Read next
- Heat shrink tape for bends a tube cannot be threaded ontoThe shrinkable answer to the same geometry problem, and where it beats a hand wrap
- Mastic tapeWhat goes underneath a build-up to kill the void before you start wrapping
- Heat shrink tape vs electrical tapeWhy a PVC roll off the van is not a substitute for either of them
- Reading a heat shrink datasheet without taking it on trustWhat ASTM D149, ASTM D257 and BS 903 actually measure
- Why wraparound sleeve repairs fail in the groundThe seam and the void, seen on parts that were dug back up
Send the shape, not the part number
Give the substrate, the jacket material, the diameter or bar section, the wall thickness your specification calls for and the working temperature. Roll width and quantity come back against that, instead of against a guess.