Jointing tape against a heat-shrink sleeve

Q: What is the waterproof tape in a cable joint kit called?

Mastic sealing tape on most kit lists. GPS/1112 names it beside copper woven flexible mesh tape. GXSS-1236 names red insulating mastic tape. GLT-1100 names black mastic sealing tape. Order against the codes: HBMT black, HRMT red, HSCM yellow.

Q: Which cable joint compound goes on the connector?

On GTJ/2436 the connector gets stress relief mastic at item 2, six pieces. The semi-con cut end on the XLPE side gets stress control mastic at item 7, six more. The yellow line is HSCM-06 or HSCM-09. Two separate manifest lines, not interchangeable.

Both are in the kit. The argument is only ever about which one carries the duty.

Every part in a joint kit, named

What the tape in the box is actually for

Open a GXS or a GPS kit and you reach tape before you reach a sleeve. Most of it is not insulation.

The kit lists say so plainly. GPS/1112 carries mastic sealing tape, glass cushion tape and copper woven flexible mesh tape. GXSS-1236 carries red insulating mastic tape, copper woven mesh and GI mesh. Glass cushion tape, copper mesh and GI mesh are mechanical or screening materials. Only the mastic is a sealant.

Mastic tape is a cold-applied butyl sealant, supplied for use with the manufacturer's joint and termination kits. That description is the manufacturer's own, on its Mastic Tape datasheet. It is narrower than the claim the trade usually makes for a roll of tape. The kits are manufactured by Gala Thermo Shrink Pvt. Ltd. of Mumbai; this site sells nothing.

One row on that datasheet deserves a second look. Adhesion and self-amalgamation are rated Good for all three mastics, with no figure and no test method attached. Every other row on the sheet carries both.

Three mastics, three different jobs

The three colours are not one product in three tints. Each has its own code, its own place in the kit and its own electrical brief.

The dielectric constant row gives the game away. Black is 2 to 3, red 3 max, yellow 10 min, all to ASTM D150. Volume resistivity runs the other way: red at 1 × 10¹⁴ Ω·cm min. against yellow at 1 × 10⁹ Ω·cm min., to ASTM D257.

So the yellow one is deliberately the least insulating material in the box. High permittivity is the whole point of it. The GTJ/2436 kit list says the same thing in plain words at item 5: high permittivity void filler.

The three mastic lines, by code

Widths, thicknesses and codes are from the manufacturer's Mastic Tape datasheet. Every code below is supplied in strip or roll form, cold, with no torch.

Gala code	Colour	Where it goes	Width (min.)	Thickness (±5%)
HBMT-01 to HBMT-15	Black	Water sealing and weatherproofing on LV and MV joints, terminations and telecom work	35 mm	2.5 mm
HRMT-01 to HRMT-19	Red	Watertight seal on breakout boots, non-tracking tube and lugs in MV terminations	35 mm	2.0 mm on HRMT-01 and HRMT-02, 1.7 mm on the rest
HSCM-06 and HSCM-09	Yellow	Stress relief void filling on connectors and at screen cuts	20 mm and 25 mm	1.7 mm

Mastic against a heat-shrink sleeve, on published figures

Mastic figures come from the Mastic Tape datasheet. Sleeve figures come from the manufacturer's cable repair sleeve page. Read the method before you read the value.

Property	Black HBMT	Red HRMT	Yellow HSCM	Heat-shrink repair sleeve
Tensile strength, ASTM D638	0.1 MPa min.	0.5 MPa min.	0.1 MPa min.	12 N/mm² min.
Ultimate elongation, ASTM D638	300% min.	300% min.	300% min.	300% min.
Dielectric strength	6 kV/mm min., ASTM D149	10 kV/mm min., ASTM D149	15 kV/mm min., ASTM D149	above 15 kV/mm, ASTM D2671
Dielectric constant, ASTM D150	2 to 3	3 max.	10 min.	3.0 max.
Volume resistivity, ASTM D257	1 × 10¹⁰ Ω·cm min.	1 × 10¹⁴ Ω·cm min.	1 × 10⁹ Ω·cm min.	no figure on the page or the sheet
Service temperature, IEC 216	−20 to +90 °C	−20 to +90 °C	−20 to +90 °C	−55 to +125 °C on the outer wall
Density, ASTM D792	1.30 ± 0.2 g/cm³	1.20 ± 0.2 g/cm³	1.30 ± 0.2 g/cm³	specific gravity 1.4
Ingress protection claimed	none published	none published	none published	IP68 from the hot melt adhesive lining

What those numbers settle, and what they do not

The tensile row settles the mechanical question on its own. Black mastic is specified at 0.1 MPa minimum. The repair sleeve is specified at 12 N/mm² minimum, on the same ASTM D638. One megapascal is one newton per square millimetre, so that is a hundred-fold gap in the property that resists a pull across the join.

Elongation is identical at 300% minimum on both. Tape does not lose this argument on stretch. It loses it on load.

Read the dielectric strength row with more care than the rest. The mastics are tested to ASTM D149 and the sleeve to ASTM D2671. Setting 15 kV/mm for yellow mastic beside 15 kV/mm for the sleeve compares two different tests.

The temperature band matters more than either figure. Mastic is rated −20 to +90 °C to IEC 216. A GXLT/GPLT joint is type tested through 63 heating cycles at 95 °C conductor temperature. Mastic never sits at conductor temperature. Still, check that band against the cable's rating before a wrap carries a seal alone.

No source for that

Three questions a jointer will ask that none of these sheets answers. Cold flow: no creep or flow figure under pressure, and no test method, anywhere on the Mastic Tape sheet. Overlap: the GMRS sleeve gets a published minimum overlap, 25 mm, 50 mm or 75 mm by size. The tape gets no turns, half-lap or tension figure at all. Ageing: the sheet claims UV and weather resistance for all three mastics, with no exposure hours and no standard against it. Ask the manufacturer before you build a service life on any of the three.

Where tape is the right answer

The first two are jobs where the manufacturer's own heat-shrink kit is the wrong tool. That is worth saying plainly.

No hot work permit. Heat shrink needs a naked flame. Where the permit is refused, nothing that needs a torch goes on, and mastic is the only thing in the bag that works cold. For a permanent cold repair the same range carries cold shrink tubing and cold shrink breakouts in EPDM, listed on the component page.
A void no moulded shape fits. Stress relief mastic exists because a recovered sleeve cannot fill the step at a screen cut, or the shoulder of a barrier connector. GTJ/2436 ships six pieces of it, and six more of stress control mastic.
Under the sleeve, never instead of it. Red mastic seals the boot legs and the lug. A recovered sleeve on its own leaves a leak path at the crutch.
Holding the sleeve shut. The cable repairing sleeve is folded round the cable, taped up with heat resistant tape, then shrunk. That sequence is in the manufacturer's own wrap-around sleeve datasheet. Tape does the setting-out. The sleeve does the sealing.

Where tape loses the argument outright

Buried or submerged. IP68 is claimed for the repair sleeve's hot melt adhesive lining. No ingress protection rating is published for any of the three mastics.
Screened MV cable. A joint on screened cable has to rebuild a semi-conducting screen, a stress control layer and a metallic screen. GXS/1236 does that with a stress control sleeve, screened dual wall tubing, copper woven flexible mesh tape and GI mesh. Yellow mastic grades the field across a void; it does not replace the stress control sleeve.
Anything with a defined recovered wall. The wrap-around sleeve holds a 2.7 mm recovered wall from GWS-55/8 through GWS-240/50. Tape runs 1.7 mm to 2.5 mm per layer, with no stated layer count. The finished wall is whatever the jointer wrapped.
Anything type tested. GXLT/GPLT is tested with the joint immersed in water. AC withstand is 3.5 kV and 6 kV for 5 minutes, impulse 8 kV and 12 kV, then 63 heating cycles, to IEC 60502, IEC 60060 and IEC 60230. That record belongs to the kit, and it does not transfer to a hand-wrapped substitute.

So which one carries the duty

Count the lines on a real kit. GTJ/2436 runs to twenty numbered components and eight installation aids. Five of those twenty-eight lines carry the word tape or mastic, and one of the five is emery.

None of the five carries the withstand. That sits on the screened tubing at item 9, the dual wall tubing at item 10 and the outer jacketing at item 19.

So the honest conclusion is not that one beats the other. Both ship in the same box, sized to the same cable. The specifier's job is to say which line does which duty.

Give tape a code and a position on the manifest. Do not give it a sleeve's job. If a roll of tape is the entire answer to a jointing question, no joint is being made.

Questions that come up on site

Can a cable joint be made with self-amalgamating tape alone?

Nothing published here covers a hand-wrapped joint. The withstand and cycling tests are run on assembled kits, and the lowest kit in the range is GXLT/GPLT at 1.1 kV and 3.3 kV. That record is what a tender asks for, and a wrap cannot inherit it.

Is mastic tape the same thing as insulating tape?

No. Mastic tape is a cold-applied butyl sealant. Black holds 6 kV/mm min. and red 10 kV/mm min. to ASTM D149, so both stand off voltage, but the sheet sells them on sealing and weatherproofing. Yellow is the inverse of insulation: dielectric constant 10 min., volume resistivity 1 × 10⁹ Ω·cm min.

What is the waterproof tape in a cable joint kit called?

Mastic sealing tape on most kit lists. GPS/1112 names it beside copper woven flexible mesh tape. GXSS-1236 names red insulating mastic tape. GLT-1100 names black mastic sealing tape. Order against the codes: HBMT black, HRMT red, HSCM yellow.

Which cable joint compound goes on the connector?

On GTJ/2436 the connector gets stress relief mastic at item 2, six pieces. The semi-con cut end on the XLPE side gets stress control mastic at item 7, six more. The yellow line is HSCM-06 or HSCM-09. Two separate manifest lines, not interchangeable.

Can an existing heat-shrink sleeve be overwrapped with tape?

The mastics are rated adhesive and self-amalgamating, so it will stick. But no sheet covers a wrap over an already recovered sleeve, and no adhesion-to-polyolefin figure or shelf life is published. For a damaged jacket the manufacturer's answer is a wrap-around repair sleeve: GMRS-19 to GMRS-250, 5 to 192 mm cable OD.