Bench questions
Shrink tube questions we get asked from the bench
Eight answers off the published charts — 0.78 mm of recovered wall, 125 °C to recover, 12 kV/mm, 1.1 kV — and the three blanks no sheet in this range fills.
What it does, and which row to order
What is heat shrink tubing used for?
Every series publishes its own application line, so the answer is a list of codes rather than a list of virtues. GLC and GSC, 2:1: light-duty wire harnessing, in-line component insulation, strain relief where a conductor leaves a terminal, busbar insulation inside switchgear, and colour coding — GSC/YG carries the yellow-and-green stripe kept for earth leads. GLC3, 3:1: tunnels and mines, to 600 V. GMW: environmental protection and connector insulation on low-voltage terminations and straight-through joints. GHW: mechanical protection and outer sealing of underground joints. GDW: splice and harness sealing in automotive, telecommunication, industrial and avionics wiring. GMW 5x: the transition from a connector back shell down to the cable behind it. GLC-SV: wind-power anchor bolts, U-bolts and automotive fasteners. GDLT: the insulating and screening layer inside a joint. GCTE: inline connections and terminal lugs, with no heat at any point.
What is the purpose of it, in one sentence?
To hold one chosen diameter against a substrate for as long as the assembly is in service, and to bring whatever lines the bore into contact with it on the way down. The lining decides the rest: bare wall gives insulation and abrasion resistance, hot-melt adhesive gives a seal to IP68, a semi-conductive layer manages a field instead of excluding it. Past 5:1 — the widest ratio published here — or with more than one outlet, nothing extruded closes it, and the part is a moulded shape.
The cable measures 16 mm. Which row?
Two diameters decide it and the cable is only one. The largest thing the tube travels over sets the supplied ID; the smallest thing it grips sets the recovered ID. On a bare 16 mm run, GLC 25.0/12.5 is the comfortable row — 9 mm of clearance to thread through, 12.5 mm recovered sitting 3.5 mm under the cable so the wall arrives tight rather than touching, and 0.78 mm of it. GLC 20.0/10.0 closes too, on 4 mm. Add a lug palm and every millimetre of it pushes you up the supplied column, the recovered column climbing with it: GLC 30.0/15.0 still works, because 15.0 is under 16, and GLC 40.0/20.0 does not — it recovers to 20.0 mm and never reaches the cable. That is where a 2:1 ladder ends, and the fix is ratio, not size. GDW 39/13 clears 39 mm and closes to 13 with 0.9 mm of hot melt in the bore; GMW 5x 50/10 clears 50 and closes to 10 behind a 4.3 mm wall. Every series on one ladder: heat shrink size chart.
Can a length come off and go back on?
No, and the reason is dimensional rather than thermal. The expanded bore is stored geometry, spent once the wall passes recovery and cools at the smaller diameter; taking a length off is a knife job and what comes away is scrap. A piece that stopped part-way is the opposite case — unspent memory is still in it and a further pass keeps closing it, within the limits on installing heat shrink tube. The cold-shrink sheets say it plainly: every GCTE part is factory expanded onto a removable core, and nothing in this library describes expanding anything anywhere else.
Heat, storage, and what a rating covers
Will a lighter do it?
No, and the gap is not marginal. GMW and GHW publish a shrink temperature of 125 °C against IEC 216 and GDLT 135 °C; no thin-wall sheet here publishes one at all, since vented GLC-SV and the GSC marking sheet stop at a continuous limit and the GLC sheet carries only a selection chart. Those numbers belong to the wall, right round the bore — a hot air gun heats the circumference, a flame heats the face it is aimed at. The heat-shock rows show what the compound genuinely takes: 250 °C for 30 minutes on GMW, GHW, GMW 5x and GDLT to ESI 09-11, four hours at the same temperature on the thin-wall sheets, each with no dripping, cracking or flowing — an oven, evenly, on the whole part. Nor is one figure safe on its own: GDLT prints 135 °C in its table and, in its own feature list, minimum shrink 100 °C with full shrink at 130 °C. Instrument, distance and stroke order: installing heat shrink tube.
Is there a shelf life, and how should stock be kept?
Nothing in this range answers it. Across every tube sheet here, heat shrink and cold shrink alike, there is no shelf life, no storage band and no date-code convention. What the sheets do fix is the state each technology waits in. Heat shrink waits expanded but unstressed — GLC on 100 m spools at the small sizes, 25 m at GLC 100/50.0, or 1.2 m cut lengths, 175 to a box at GLC 8.0/4.0 and five at GLC 100/50.0. Cold shrink waits stretched: GCTE 20/7 sits on its core at 20 mm and free-recovers to 7 mm, GCTE 104/42 at 104 down to 42, and that strain is held from the day the part was made — the argument for turning that stock first, though no sheet bounds it. The only wording anywhere near a claim sits on the end-cap sheet, a part this site does not cover, and it names no period. One thing the charts do settle: EPDM and silicone publish the same seven GCTE codes with identical Ds, Df and Lf, so the code on the bag does not say which rubber is on the core.
What is any of this rated to?
Four ceilings, in the table below, and swapping one for another is how a specification goes wrong. GHW at 36 kV mechanically protects and outer-seals an underground joint; it does not insulate a bare conductor at 36 kV on its own. And kV/mm is not a class: silicone cold shrink publishes 18.0 kV/mm to ASTM D149 and is rated to 1.1 kV, while GMW and GHW publish 12 kV/mm and carry 3.3 kV and 36 kV. The highest figure sits on the lowest-rated part, because dielectric strength is measured on a test piece and a class comes from a type test on the assembly. GMW 5x prints the same 12 kV/mm with the qualifier that makes the point — at a 2 mm wall. On the GMW/GHW sheet itself the property table says 12 and the feature list beside it says 15. The standards, decoded.
Is it only for cable?
No, and the non-cable list is published rather than inferred. Vented GLC-SV, 20/10 to 70/35 at 0.78 to 1.10 mm of recovered wall, exists for wind-power anchor bolts, U-bolts and automotive fasteners, its internal air-vent groove pulling it down over a bend wrinkle-free with no grease behind it. GMWR 9/3 to 50/16 and GHWR 12/3 to 50/16, both 3:1, coat the U-bolt-to-pipe contact point, which the manufacturer's sheet calls the leading cause of process pipe failure. The same explainer adds re-gripping tool handles and joining two splices with a conductive-polymer-lined tube instead of solder. Absent everywhere is a structural duty: the only strength figures are tensile and elongation on a test piece — 10 N/mm² minimum on GMW and GHW, 12 N/mm² on GMW 5x, both ASTM D638 — and nothing rates a recovered tube to carry load. Over a pipe support it is a corrosion barrier and stops there (pipe supports and pipe joints); bundling and marking sit on wire harness tube.
Four ceilings, and one column that is not a rating
| Rating | Series | Dielectric strength on the same sheet |
|---|---|---|
| 600 V | GLC3 thin wall, 3:1 — tunnels and mines | not published |
| 1.1 kV | GCTE cold shrink, EPDM | 14.3 kV/mm, ASTM D149 |
| 1.1 kV | GCTE cold shrink, silicone | 18.0 kV/mm min, ASTM D149 |
| 3.3 kV | GLC and GSC thin wall, 2:1 | not published on the GLC sheet |
| 3.3 kV | GMW medium wall, 3:1 | 12 kV/mm min, ASTM D149 |
| 36 kV | GHW heavy wall, 3:1 | 12 kV/mm min, ASTM D149 |
| 36 kV | GDLT double layer, inner and outer | 20 kV/mm min on the inner layer, ASTM D149 |
The last column is a test-piece property, not a class, and it does not rank with the first. The highest figure in the table sits on the lowest-rated part.
Three blanks, and why they stay blank
Every figure above came off a published selection chart or property table, and a chart stops at diameters, walls, materials and test methods. Three questions fall outside it. No tube sheet in this range states a shelf life, a storage band or a date code. None names an instrument or an air temperature for recovery — only the 125 °C and 135 °C the wall has to reach. And none carries a price, lead time, minimum order or stock position, so none is published here rather than estimated.
Where each answer is worked out in full
Short answers above; the arithmetic, the full charts and the places two sources disagree are on these pages.
- Heat shrink size chartEvery series on one supplied-ID and recovered-ID ladder.
- Shrink ratio explainedWhat each ratio band changes, and what it leaves alone.
- Installing heat shrink tubeHeat source, distance, stroke order, and the bead that proves a seal.
- Why a recovered tube failsFive faults, each read off the finished part.
- Heat shrink or cold shrinkTwo recovery mechanisms, and the 1.1 kV line that settles the choice.
- Thin wall tube datasheet (PDF)The manufacturer's own GLC selection chart.
- Cold shrink tubing datasheet (PDF)The GCTE chart and the EPDM property table.
Five facts turn one email into one answer
An enquiry answered in one reply carries five things: the smallest diameter the tube must grip, the largest obstruction it must pass, the length, the voltage, and whether the site permits hot work. The last decides heat shrink or cold shrink before any chart is opened.