Reading the sheet
How to read an insulating cover datasheet
Four materials, about twenty rows of test data, and the four lines that actually change the part code.
Twenty rows, four of which decide
A 12 kV busbar tee under a 1.0 mm polyolefin wall, and a 38 mm bare conductor under a 2.0 mm silicone wrap. Both parts sit behind a technical table of roughly twenty rows, and on both sheets only four of those rows change what gets ordered. The remainder describe the compound.
Begin with the heading over the value column, because it is not the same on every sheet. The polyolefin shroud table is headed TEST DESCRIPTION / RECORDED VALUE / TEST METHOD. The Insulcover line cover table is headed PROPERTY / VALUE / TEST METHOD. The self-locking silicone table is headed PROPERTIES / TEST METHOD / TYPICAL VALUE, and it carries a footnote calling its figures typical analytical values obtained under controlled laboratory conditions, which should not be read as product specifications.
That footnote is doing real work. A recorded value came off a test on that construction; a typical value describes what the compound generally does. Neither one is a floor unless the cell itself says (min.) — and most of the rows worth quoting do.
The four materials, as each one is published
One column per material, each taken from a single named source so the figures stay comparable: flexible PVC from the manufacturer's published table for the PVC busbar shroud, cross-linked polyolefin from the polyolefin shroud sheet, EPDM from the GTPE-500 terminal protector sheet, silicone from the GSOC self-locking line cover sheet. "Not published" means that source carries no row for the property, not that the property is poor.
| Property | Flexible PVC | Cross-linked polyolefin | EPDM | Silicone | Test method |
|---|---|---|---|---|---|
| Dielectric strength | 16 kV/mm (min.) | 22 kV/mm (min.) | 15 kV/mm (min.) | > 210 kV/cm | ASTM D149 |
| Tensile strength | 12 N/mm² (min.) | 9 N/mm² (min.) | 10 N/mm² (min.) | 7 N/mm² (min.) | ASTM D638 |
| Ultimate elongation | 350 % (min.) | 300 % (min.) | 200 % (min.) | 300 % (min.) | ASTM D638 |
| Hardness | 65 ± 5 Shore A | 45 ± 10 Shore D | 35 ± 5 Shore D | Not published | ASTM D2240 |
| Continuous temperature limit | −20 to +115 °C | −40 to +115 °C | −40 to +115 °C | Not published | IEC 216 |
| Water absorption | Not published | 0.5 % (max.) | 0.5 % (max.) | 0.5 % (max.) | ASTM D570 |
| Volume resistivity | Not published | 1 × 10¹³ Ohm·cm (min.) | 1 × 10¹³ (units not printed) | 1 × 10¹³ Ohm·cm (min.) | ASTM D257 |
| Tracking and erosion | Not published | Endpoint only, 3.25 kV for 20 min | Not published | Full ladder, ending 3.25 kV for 20 min | ASTM D2303 |
| Flammability | Pass | Not published | Not published | Not published | UL 94-V0 |
| AC withstand, 1 min at 12 kV | Not published | Not published | 28 kV | Not published | No method named |
20 or 22 kV/mm: two products, never an average
The polyolefin column above reads 22 kV/mm (min., ASTM D149). The wrap-around line cover moulded in the same material family reads 20 kV/mm (min., ASTM D149). Two products, two compounds, two sheets — the gap is not a rounding error to be split down the middle, and a table that averages them is describing nothing that exists.
The 22 kV/mm figure belongs to the moulded part fitted over an assembled connection indoors. The 20 kV/mm figure belongs to the wrap fitted onto a bare conductor outdoors. Quote whichever one names the part on the order, and quote the document with it.
Once the table is read, the shortcut is short. Indoors, on a terminal or a made joint, with colour identification wanted: flexible PVC. Outdoors, cold, or in an acid, alkali or salt atmosphere: cross-linked polyolefin. Inside an enclosure that has to be opened repeatedly for direct voltage testing: EPDM. Up a pole with nothing in the bucket but hands: silicone.
One cover, four documents, four sets of numbers
| Published in | Tensile strength (ASTM D638) | Ultimate elongation (ASTM D638) | Hardness (ASTM D2240) | Dielectric strength |
|---|---|---|---|---|
| Overhead-Line-Cover-Insulcover.pdf | 10 N/mm² (min.) | 400 % (min.) | 40 ± 5 Shore D | 20 kV/mm (min., ASTM D149) |
| Overhead-Line-Cover-Insulcover1.pdf and the earlier _old sheet | 13 N/mm² (min.) | 300 % (min.) | 45 ± 10 Shore D | 25 kV/mm (min., IEC 243) |
| Insulation-Enhancement-Products.pdf | 9 N/mm² (min.) | 250 % (min.) | 40 ± 5 Shore D | 20 kV/mm (min., ASTM D149) |
| The manufacturer's Insulcover product page | 9 N/mm² (min.) | 250 % (min.) | 40 ± 5 Shore D | 20 kV/mm (min., ASTM D149) |
All four are published by the manufacturer for the same GOC wrap-around Insulcover. Listed by document rather than by date, because the recent sheets carry an issue number and month in the footer — the GTPE-500 sheet reads Issue 1, Jan. 2024 — while the two older Insulcover sheets carry none.
Four documents, one part: quote the lowest and name the source
Tensile strength for the same GOC series is published at 9, 10 and 13 N/mm². Elongation at 250, 300 and 400 %. Dielectric strength at 20 kV/mm against ASTM D149 on the recent documents and 25 kV/mm against IEC 243 on the older pair — a different method as well as a different number, so those two cells do not belong in one column. Specify against the lowest published figure, write the document name into the enquiry, and have the manufacturer confirm which issue is current before anything reaches a tender.
Marks, files and report numbers, decoded
- UL File E335936
- An Underwriters Laboratories file covering the Busboot shroud and the Bustube sleeve. A file number is held against named products, not against a company or a whole catalogue — the heat-shrink tubes sit under a separate file, E328538.
- UL 94-V0
- A flammability class describing how a material burns and self-extinguishes. The PVC shroud and the PVC busbar end cap are both published as passing to it. It is a burn classification rather than a listing, and it carries no dielectric meaning whatever.
- ANSI C37.20.2
- The metal-clad switchgear assembly standard. Several covers here are published as tested against it for switchgear service at medium voltage, to a 36 kV ceiling — meaning the cover was proved inside the duty that assembly standard sets. The same publisher's busbar reference at busbarsleeves.com takes it apart row by row.
- ASTM D149
- Dielectric strength, published per millimetre of wall. This is why the thickness ladder outranks the headline figure: 1.0 mm of 22 kV/mm polyolefin and 2.00 mm of 16 kV/mm PVC are both published for the same 12 kV class.
- IEC 216
- The continuous temperature limit, always a pair. The hot end almost never separates two candidates; the cold end does, and it is the end that gets skipped.
- IEC 243
- An older dielectric strength method. A figure carrying IEC 243 instead of ASTM D149 has come off an earlier revision, and the two cannot be tabulated against each other.
- ASTM D2303
- Tracking and erosion, run on an inclined specimen with a contaminant flowing down a wetted surface under voltage. How it is printed varies more than what it measures — see below.
- ESI 09-11
- The method named against the heat shock row on the shroud and circuit-breaker sheets. On the current polyolefin shroud sheet that is 90 °C for 30 minutes, with the result recorded as no cracking or flowing.
- Technical Qualification Report QR 1031 / QR 1036
- An internal report reference printed at the foot of the polyolefin shroud and Insulcover sheets. It is the manufacturer's own document number rather than a third-party certificate, and it is worth asking to see one.
- RoHS and REACH
- Conformity declarations made by the manufacturer and printed on the sheet as a logo. No body issues either of them, so read them as a statement rather than as a certificate.
- ISO 9001:2015, ISO 14001:2015, ISO 45001:2018
- Management-system certifications describing how the factory is run. Nothing inside them measures the dielectric strength, the temperature band or the surface behaviour of the part in your hand.
ASTM D2303, and the two ways it gets printed
The method looks for two separate failures on one specimen: a conductive carbon track forming along a contaminated wetted surface under voltage, and erosion of the material itself. Non-tracking, the phrase on every outdoor cover sheet in this range, is a claim about exactly that test and about nothing else.
Every polyolefin document prints one endpoint against the method: nothing tracked, nothing eroded, no flame failure, with 3.25 kV sustained across 20 minutes. The self-locking silicone sheet prints the whole ladder that led there: an hour at 2.5 kV, an hour at 2.75 kV, an hour at 3.0 kV, and then the same 20 minutes at 3.25 kV. Identical endpoint, four times as much of the run shown.
The PVC shroud's published table carries no row for the method at all, which is a fair reading of PVC as an indoor material rather than a gap somebody forgot. What either printing predicts once the cover is on the metal is handled separately.
The four lines that decide, and the ones that do not
Order-changing rows first, in the order an enquiry needs them.
- The selection chart. GOC 1A to GOC 4 by conductor diameter, GSOC-M 15 to GSOC-M 38 by the same, GTIC-1 to GTIC-3 by tab, TCV 12 to TCV 3251 by terminal, GPS 1099 to GPS 1178 by opening pattern. A code drawn from the wrong series is the wrong part however good the electrical rows beside it look.
- The wall against your voltage class. The polyolefin shroud is published at 1.0 mm minimum for 12 kV, 1.4 mm for 18 kV, 1.8 mm for 24 kV and 2.5 mm for 36 kV; the PVC shroud at 1.25 mm for 3.3 kV, reaching 4.50 mm by the time its ladder tops out at 38 kV. The class lives in this row, not in the kV/mm headline.
- The cold end of the temperature limit (IEC 216). −20 °C for the PVC parts, −40 °C for the polyolefin shroud and the EPDM protector, −45 °C for the wrap-around line cover. Nothing published in this range goes below −45 °C, so a duty colder than that is a question for the manufacturer rather than a column to search.
- Whether a fitting tool is named. Insulcover is published as installed with the Split Insulation Tube Tool, which stays in one location for the fit; GSOC is published as needing no special tool. That one line decides whether a crew can do the job with what is already in the bucket.
- Reassurance, not selection: density 1.20 ± 0.2 gm/cm³ (ASTM D792), dielectric constant 5 (max., ASTM D150), volume resistivity 1 × 10¹³ Ohm·cm (min., ASTM D257) and water absorption 0.5 % (max., ASTM D570) repeat almost unchanged across the whole range. They confirm a compound is what it says; they will not separate two candidates.
- Check the method column against the property beside it. On the manufacturer's own circuit-breaker boot page the volume resistivity row is referenced to ASTM D2303, which is the tracking and erosion method, and the selection chart above it lists GOC 1 to GOC 4 — the overhead line cover series. Tables get pasted onto neighbouring products, and the part codes are the giveaway.
Not published anywhere in this range — ask for it
No line cover, shroud, cap or cover-up document here publishes a partial discharge limit or a power-frequency withstand voltage for the fitted cover. One part breaks that: the EPDM terminal protector publishes 28 kV for one minute and 75 kV impulse at 12 kV, and 50 kV and 125 kV at 24 kV. The screened separable connector — a connector, not a cover — publishes ≤ 10 pC at 1.73 U₀. So the manufacturer does measure these where the product calls for it, in its own high-voltage and partial-discharge labs. If a specification demands a withstand or a PD limit on a cover, that is a question to put to those labs; none of these sheets answers it.
The sheet you are holding, and the page that decodes it
- Cross-linked polyolefin wrap-around cover (GOC)20 kV/mm (ASTM D149), five sizes, tool required
- Silicone line covers (GSOC and GSIOC)Four voltage classes, no tool, typical values
- Shrouds over an assembled connectionPVC at 16 kV/mm against polyolefin at 22 kV/mm
- Caps and covers over terminals and tabsTCV and GTIC series, sized by the terminal
- Pre-formed cover-ups over insulators and bus connectionsChosen by opening pattern, not by a spec row
- What each test method predicts in serviceTracking, UV, cold, and the refitting failure
- Fitting a cover, and taking it off againWhere the tool line ends up mattering most
Quote the document, not just the number
Send the part code, the document name, the issue where the footer carries one, and the conductor or bar dimension the cover has to fit. A figure with no source behind it cannot be checked by anyone, and the four Insulcover documents above are why that matters here.