In air → submerged · the cable side
A cut cable end, from a dry store to a flooded duct
The band decides the type of cap. The jacket diameter only decides which one of that type you order.
Put the end on the scale before you look at a part number
A drum under a roof is in air. The same drum in an open yard through a monsoon is in the splash zone. A spare end coiled into a duct or left in a backfilled trench is buried, and the day that duct takes water it is submerged. An end can cross all four bands between the works and the joint bay, so choose for the deepest band it will ever see, not the one it is sitting in when the order is raised.
Two limits before anything else. There is no cold-shrink end cap in the manufacturer's published data, so where a hot-work permit rules out a torch the honest answer here is a push-on cap; the no-flame case has its own page. And nothing on this site is a price, a tariff code or a stock position.
Everything below hangs off one distinction: a cap that seals versus a cap that covers. An adhesive-lined heat-shrink cap seals — the lining softens under the torch, wets the jacket and stays bridged to it as the part cools, and IP68 is the published rating for that construction. A push-on PVC cap covers. It keeps weathering, moisture and contamination off the end, it is held on by fit alone, and no ingress rating is published for it. Both are legitimate parts and they are not substitutes.
Which jackets the lined caps seal to, and why the lining is there
The lined caps are made to seal onto XLPE, PVC, PILC and rubber-sheathed jackets. Condition matters more than material. A sheath gone oval under drum pressure, ridged over the armour bedding, or nicked by a stripping knife will not seal by interference against anything: there is a leak path running the length of the contact face, and squeezing harder does not close it.
That is what the adhesive is for. It flows into those gaps while hot and holds the bridge once cold — a bond to the sheath rather than a grip on it. It also settles the re-use question. A shrunk seal is published as permanent, not removable and not re-usable, so a cap that has been fitted once is scrap the moment it comes off.
One coded range covers the cable side: GEC 001S to GEC 1101, spanning published cable diameters from 2–4 mm up to 230–460 mm. Inside that span a cap exists and the rest of this page is about which of the five it should be. Outside it, the conversation is a moulding one.
Five ways to close the end, side by side
Torch access and re-entry eliminate more candidates than voltage class does.
| Cap type | Torch on site | Ingress rating published | Re-entry | Cost basis per end |
|---|---|---|---|---|
| Adhesive-lined heat-shrink (GEC) | Required | IP68 | None — cut it off, fit a new one | One moulded part |
| Relief-valved heat-shrink (GEC RV) | Required | IP68 | Not needed — the valve vents while the cap stays on | One part plus a factory-tested valve |
| Live end cap (GLEC) | Required | Not stated on the live-cap sheet | None | Five pieces per end: four inner caps, one thick-wall outer |
| Tamper-proof end seal | Required | IP68 | None by design — that is the function being bought | One part plus printing specified at order |
| Push-on PVC cap | Not required — pushed on by hand | None; this one covers rather than seals | Yes — pull it off, push it back on | Published as more economical than heat shrink |
Each one has its own page
Seven parts sit on the cable side. Poles, piles, anodes and panel terminals are elsewhere, because nobody arrives at them through a cable question.
Adhesive-lined end cap
The plain sealed cap: cross-linked polyolefin body, hot-melt lining. Specify it where the end goes into a duct or a trench and nobody looks at it again.
Relief-valved de-gassing cap
For ends at 33 kV and above, where gas keeps evolving inside the cable in a hot yard. The valve releases above 3 psi and is non-returnable.
Live end cap
Each core is capped separately, then a thick-wall outer cap goes over the assembly carrying a flash symbol. Coded by conductor cross-section, not jacket diameter.
Tamper-proof end seal
The same sealed body, printed in ink that cannot be lifted. It cannot be removed or re-used once shrunk, which is what makes a short-length claim on arrival arguable.
End cap with a pulling eye
Closes a duct-bound end and gives the winch something to pull on. The eye is set into the crown rather than strapped over a plain cap.
Push-on PVC cap
Polyvinyl chloride, pushed on by hand, no tools and no skill. Custom lengths and thicknesses without a tooling charge, and it does not crack or split the way low-density polyethylene does.
Entry seals where the cable enters the box
An end cap closes an end that is going nowhere for now. A gland seals the same cable where it passes into an enclosure and has to stay passed through.
The two materials, and the method behind every figure
| Property | Cross-linked polyolefin (heat-shrink caps) | PVC (push-on caps) | Test method |
|---|---|---|---|
| Dielectric strength | 12 kV/mm min. | 12 kV/mm min. | ASTM D149 |
| Tensile strength | 12 N/mm² min. | 12 N/mm² min. | ASTM D638 |
| Ultimate elongation | 350% min. | 350% min. | ASTM D638 |
| Density | 1.05 ± 0.2 g/cm³ | 1.23 g/cm³ | ASTM D792 |
| Hardness | 45 ± 10 Shore D | 65 ± 5 Shore A | ASTM D2240 |
| Water absorption | 0.2% max. | Not published | ASTM D570 |
| Volume resistivity | 1 × 10¹⁴ ohm.cm min. | Not published | ASTM D257 |
| Dielectric constant | 5 max. | Not published | ASTM D150 |
| Continuous temperature limit | −40 °C to +110 °C | −20 °C to +115 °C | IEC 216 |
| Shrink temperature | 125 °C | Not applicable — push-on | IEC 216 |
| Low-temperature flexibility, −40 °C for 4 hours | No cracking | Not published | ASTM D2671 |
| Heat shock, 250 °C for 30 minutes | No cracking or flowing | Not published | ESI 09-11 |
| Flammability | Not published | Pass | UL 94-V0 |
Polyolefin values are those published for the adhesive-lined and tamper-proof caps, which share one table; PVC values come from the push-on cap sheet. "Not published" means absent from the sheet, not zero. Source: Heat Shrink Cable End Caps.
The questions that come in before an order
Is a push-on PVC cap waterproof?
The old cap has a code on it I cannot read. What do I quote?
Why would a cap need a valve at all?
Can I take a cap off, test the core, and put it back?
Before you raise the enquiry
The working detail this hub deliberately does not repeat.
- Four size charts, and how to read a code before you quote itGEC, GEC RV, GLEC and the gland chart, with what each column measures.
- What the tests on an end-cap datasheet actually proveEvery standard named in the table above, explained once.
- Six ways a closed end opens againEach failure set against the band it happens in.
- Fitting a cap with a gas torch, on five different substratesPublished shrink temperature is 125 °C; the substrate decides the technique.
- The manufacturer's Insulcap page, for the ordering variantsWhere the valved telecom variant and the conductive mastic option are listed.
Send the dimension, not the part number
A jacket diameter in millimetres, the core count, the voltage class and the deepest band the end will sit in are enough to return a size code first time.