Kit component · creepage extension
Rain sheds: what they do, what size, and how many per core
Five inputs settle the shed count: cable construction, core count, conductor size in mm², Umax, and indoor or outdoor.
Insulshed rain shed, GRS 130 series and GHSG tri-core
A shed ring shrinks onto a terminated core and lengthens the surface path between lug and earth, leaving the kit's tail length untouched.
- Listed as a component distinct from the non-tracking weather-resistant tubing in every GXO/E and GPO/E kit
- Single-core sheds are lined with water-resistant mastic; the tri-core shed carries factory-applied hot melt adhesive sealing to wire and cable jackets
- Supplied inside the outdoor termination kits; indoor kits across most series carry none
- Ten single-core sizes and three tri-core sizes, the single-core range charted on skirt diameter ØA from 88 mm to 200 mm
| Material | Cross-linked polyolefin, non-tracking |
|---|---|
| Internal coating | Water-resistant mastic |
| Tracking and erosion | No tracking, erosion or flame failure up to 3.25 kV for 20 min [ASTM D2303] |
| Dielectric strength | 15 kV/mm (min) [ASTM D149] |
| Volume resistivity | 1 x 10¹⁴ ohm.cm (min) [ASTM D257] |
| Shrink temperature | 125 °C [IEC 216] |
| Single-core designations | Ten sizes, GRS 130-1 to GRS 130-6, including the -1 N, -2 N, -3 N and -6 S variants |
| Tri-core designations | GRST-1, GRST-2, GRST-3 |
| Service | Indoor and outdoor |
What a shed is buying you
Creepage is the surface distance a leakage current has to travel from the terminal lug down to the earthed gland plate. On a dry day that distance is generous. Rain wets the whole of it at once, and salt or cement dust turns the wetted film into a conductor.
A skirt breaks the film. Each ring adds surface length and keeps its own underside out of falling rain, so the path is segmented rather than merely stretched on a drawing.
The obvious alternative is a longer tail, and the kits do not offer one. Tail length is fixed by kit code: 600 mm outdoor and 450 mm indoor on every GXO/E series, 800 mm outdoor and 550 mm indoor on GPO/E-1524, and 900, 800 and 600 mm outdoor on GXOS/E at 36 kV, 24 kV and 12 kV. Sheds add creepage inside that fixed envelope, which is the whole reason the component exists.
The material is a cross-linked polyolefin with non-tracking behaviour, coated internally with water-resistant mastic and rated for indoor and outdoor service. Its tracking claim is a test result rather than a description: no tracking, erosion or flame failure up to 3.25 kV for 20 minutes [ASTM D2303].
The two shed families
| Designation | Fits | Sealing to the core | Sizes published |
|---|---|---|---|
| GRS 130-1 to GRS 130-6 | One terminated core, single-core cable or one leg of a 3-core termination | Internal water-resistant mastic coating | Ten |
| GRST-1, GRST-2, GRST-3 | All three cores of one 3-core termination at once | Factory-applied hot melt adhesive, sealing to wire and cable jackets | Three |
Designations as published by the manufacturer. The single-core dimensions are charted below.
Insulshed GRS 130 selection chart
| Code | ØA (min) | Ds (min) | Df (max) | Hs (min) | ∠° (min) | Tf (±10%) |
|---|---|---|---|---|---|---|
| GRS 130-1 | 90 | 36 | 15 | 17 | 10 | 2.5 |
| GRS 130-1 N | 88 | 41 | 13 | 33 | 20 | 2.5 |
| GRS 130-2 | 122 | 51 | 21 | 20 | 10 | 3.0 |
| GRS 130-2 N | 117 | 55 | 18 | 40 | 20 | 3.5 |
| GRS 130-3 | 135 | 67 | 31 | 24 | 10 | 3.0 |
| GRS 130-3 N | 135 | 75 | 28 | 40 | 20 | 3.5 |
| GRS 130-4 | 138 | 80 | 35 | 30 | 10 | 3.0 |
| GRS 130-5 | 138 | 105 | 35 | 35 | 10 | 3.0 |
| GRS 130-6 S | 200 | 120 | 50 | 50 | 10 | 4.5 |
| GRS 130-6 | 200 | 150 | 50 | 45 | 20 | 4.5 |
Printed as Selection Chart (Part - III) on the manufacturer's Insulshed datasheet. ØA is the outside diameter of the skirt, Ds the internal diameter as supplied, Df the internal diameter after free recovery, Hs the skirt height, ∠ the skirt angle in degrees and Tf the recovered thickness. All dimensions in mm. The −1 N, −2 N, −3 N and −6 S rows are marked on the sheet as new sizes.
Reading the shed chart
Two figures select a shed and a third tells you what it buys. Ds has to clear the core as it goes on; Df has to close onto it once recovered. A GRS 130-2 passes over anything up to 51 mm and grips down to 21 mm, so a 35 mm² core with its non-tracking sleeve already shrunk on lands squarely in the middle of it.
ØA is what the skirt is actually for. It runs 88 mm on the smallest size to 200 mm on the largest, and the difference between ØA and Df, taken twice per shed, is the surface path each ring adds. The N rows are the deeper skirts — 33 to 40 mm of Hs against 17 to 30 mm on the plain sizes, at a 20° angle rather than 10° — so where the core diameter allows either, the N variant buys more creepage per ring.
Pairs worth noticing on a requisition: GRS 130-4 and GRS 130-5 share ØA at 138 mm and Df at 35 mm and differ only in Ds, 80 mm against 105 mm, so the choice between them is purely how big the core is going on. GRS 130-6 S and GRS 130-6 share ØA and Df too, and split on Ds at 120 mm and 150 mm.
One shed per core, or one shed over three
GHSG is the tri-core variant, sized to pass over three cores at once instead of one at a time. It arrives with hot melt adhesive already applied, so the seal to the jacket is not a site-mixed mastic joint.
The two are not graded against each other in any published document. Construction, sealing method and size count are published; a rule for preferring GRST-2 over three GRS 130 sheds on the same termination is not. Send the core spacing at the breakout crotch and the jacket outside diameter to the manufacturer and let the answer come back against those two figures.
GRS 130 against GRST, as published
| Property | Insulshed GRS 130 (single-core) | GHSG tri-core (GRST) |
|---|---|---|
| Covers | One terminated core | Three cores of one termination |
| Sizes | Ten: GRS 130-1, -1 N, -2, -2 N, -3, -3 N, -4, -5, -6 S, -6 | GRST-1, GRST-2, GRST-3 |
| Sealing | Internal water-resistant mastic coating | Factory-applied hot melt adhesive |
| Tracking and erosion [ASTM D2303] | No failure to 3.25 kV for 20 min | No failure to 3.25 kV for 20 min |
| Dielectric strength [ASTM D149] | 15 kV/mm (min) | 15 kV/mm (min) |
| Continuous temperature limit [IEC 216] | -40 to +100 °C on the datasheet; -40 to +110 °C on the product page | -40 to +100 °C |
| Published spec table | Full table, physical, thermal and electrical | Full table, physical, thermal and electrical |
Sources disagree — the continuous temperature limit
Two of the three documents agree and the third does not. The Insulshed datasheet gives a continuous temperature limit of -40 to +100 °C [IEC 216] in its technical specification, and the tri-core GHSG page gives the same figure in its own table. The single-core Insulshed page gives -40 °C to +110 °C in its feature list, for a material described identically on all three. Both figures are reported here as published and neither is averaged. Confirm which applies to the designation being ordered before a temperature clause is drafted around either one.
Sheds per core, by kit code
| Kit series | Cable and class | Outdoor | Indoor |
|---|---|---|---|
| GXOS/E-1236 | Single-core XLPE/EPR/PVC, 12 kV | 2 sheds | None |
| GXOS/E-1236 | Single-core XLPE/EPR/PVC, 24 kV | 3 sheds | 1 shed, published for 15–24 kV |
| GXOS/E-1236 | Single-core XLPE/EPR/PVC, 36 kV | 4 sheds | 2 sheds |
| GXO/E-1112 | 3-core XLPE/EPR, 12 kV | 6 per kit, 2 per core | None |
| GXO/E-1524 | 3-core XLPE/EPR, 24 kV | 9 per kit, 3 per core | 1 per core |
| GXO/E-3336 | 3-core XLPE/EPR, 36 kV | 12 per kit, 4 per core | 2 per core |
| GPO/E-1112 | 3-core PILC, 12 kV | 6 per kit, 2 per core | None |
| GPO/E-1524 | 3-core PILC, 24 kV | 9 per kit, 3 per core | 1 per core |
| GPO/E-3336 | 3-core PILC, 33/36 kV | 9 per kit, 3 per core | 2 per core |
| GLT-1100 | XLPE, PVC and paper, 1.1 / 3.3 kV | Not listed in the kit contents | Not listed in the kit contents |
| Soloterm | Polymeric cable to 33 kV | Not published | None required |
Outdoor figures are the catalogue's own Qty. column, which counts sheds per kit; the per-core figure follows by dividing by three on the three-core kits. Indoor figures are the accessories note on each kit page.
Shed count travels with the kit code, not with the crew
The count is a purchasing decision taken at requisition, and the code carries it. At 24 kV on XLPE the outdoor codes run GXO-21 to GXO-24 and the indoor codes GXE-21 to GXE-24 over 16 to 400 mm². At 33/36 kV on PILC they run GPO-31 to GPO-34 outdoor and GPE-31 to GPE-34 indoor over 35 to 400 mm². Ordering the indoor code and adding sheds from stores on site produces a termination that no longer matches any published kit content.
Two things in that table are worth reading twice. The outdoor count is a straight ladder — two sheds per core at 12 kV, three at 24 kV, four at 36 kV — everywhere except GPO/E-3336, which ships nine per kit rather than twelve and so stays at three per core where its XLPE counterpart steps to four. The indoor count is the same ladder shifted down by two: none, one per core, two per core. Indoor is not shedless; it is two classes behind.
Soloterm sits outside the pattern, and the reason is field grading rather than weather: its varistor stress-control coating is integral, so indoor units need no separate skirt.
Physical properties
| Property | Value | Standard |
|---|---|---|
| Tensile strength | 12 N/mm² (Mpa) (min.) | ASTM D638 |
| Ultimate elongation | 350 % (min) | ASTM D638 |
| Density | 1.15 ± 0.2 gm/cm³ | ASTM D792 |
| Hardness | 45 ± 10 Shore D | ASTM D2240 |
| Water absorption | 0.5 % (max.) | ASTM D570 |
Published identically in the Insulshed datasheet and in the GHSG tri-core specification table. The two ranges share a compound; only the continuous temperature limit is printed differently, and only on the single-core product page.
Thermal properties
| Property | Value | Standard |
|---|---|---|
| Accelerated ageing | 120 °C for 500 hrs | ASTM D2671 |
| Tensile strength after ageing | 11 N/mm² (Mpa) (min.) | ASTM D638 |
| Ultimate elongation after ageing | 300 % (min.) | ASTM D638 |
| Low temperature flexibility (-40 °C for 4 hrs.) | No cracking | ASTM D2671 |
| Heat shock (250 °C for 30 min.) | No cracking or flowing | ESI 09-11 |
| Shrink temperature | 125 °C | IEC 216 |
| Continuous temperature limit | -40 to +100 °C | IEC 216 |
Electrical properties
| Property | Value | Standard |
|---|---|---|
| Dielectric strength | 15 KV/mm (min) | ASTM D149 |
| Volume resistivity | 1 x 10¹⁴ Ohm.cm (min) | ASTM D257 |
| Dielectric constant | 5 (max.) | ASTM D150 |
| Resistant to track & erosion | No tracking, erosion or flame failure upto 3.25 KV for 20 min | ASTM D2303 |
Not published — ask the manufacturer
Three figures a specifier reaches for are absent from every source document, and no estimate is offered in their place. First, any mapping from pollution severity class to a required number of skirts. Second, the per-core count inside the 3-core GXO/E and GPO/E outdoor kits, which list the shed as a component without a quantity. Third, the criterion for choosing GRST over three GRS 130 sheds, and the tri-core range's own dimensions, which are not charted the way the single-core range is. Put the kit code, the core spacing and the site pollution class to the manufacturer and quote the reply.
What a shed is not
Four things a skirt does not do, each of which is a separate line item in the same kit.
- Not stress control. Field grading at the screen cut-back is the stress control tube or mastic, a distinct component in every GXO/E and GPO/E kit.
- Not the insulating layer. Non-tracking weather-resistant tubing covers the core and is a separate line in the kit, ordered as one of four distinct sleeves.
- Not a tail extension. Tail lengths of 600, 800 and 900 mm are fixed by kit code, and fitting more skirts does not raise the lug height.
- Not an LV component. GLT-1100 at 1.1 and 3.3 kV lists neither a shed nor a stress control layer anywhere in its published contents.
Questions a requisition raises
How many sheds does a 24 kV termination take?
Which GRS 130 size fits my core?
Do indoor terminations need sheds?
Can a shed be added later to a termination already in service?
What does non-tracking mean on a shed?
Is there a shed for a 66 kV termination?
Are sheds ordered separately from the kit?
Getting the shed count right first time
Quote the kit code, the core count, the conductor size in mm², Umax and indoor or outdoor. Those five settle the quantity without a second email.