Switchgear connection covers
Insulating shrouds: the removable cover over an assembled connection
An assembled elbow at 38.0 kV sits under 4.50 mm of moulded vinyl; at 3.3 kV the same shell is 1.25 mm thick, and either one comes away on its own fasteners.
Insulating shroud, vinyl (PVC) or cross-linked polyolefin
The connection is already made when this part arrives. Somebody has bolted and torqued the joint, and the shroud is a moulded shell that closes over the finished assembly along a fastener line, so undoing those fasteners hands the metal back in minutes. A sleeve cannot do that: it has to be on the bar before the joint is made, and it has to be destroyed to get at the joint afterwards. The manufacturer publishes this range under the BUSBOOT name in two materials against one 36 kV ceiling, and the material — not the voltage — is what forks the specification.
- Overlapping closure, published by the manufacturer as additional protection against flash-over
- Tooling cost is a fraction of injection moulding, and the sheet states no internal stress is moulded into the parts
- Large parts can be made without significant tooling investment; a new design mould is developed within a week
- Vinyl is highly resistant to ultraviolet and ozone and is stated as suitable indoor or outdoor
- Polyolefin is halogen free, and the sheet claims protection against corrosion by strong acid, alkali and salt
- Reduces the air clearance the connection needs, which is what lets a cubicle be drawn smaller
| Goes over | Connections already assembled: bolted joints, tees, elbows, risers |
|---|---|
| Voltage | Connections up to 36 kV, both materials |
| Vinyl wall | 1.25 mm at 3.3 kV rising to 4.50 mm at 38.0 kV |
| Polyolefin wall | 1.0 mm at 12 kV rising to 2.5 mm at 36 kV |
| Dielectric strength | Vinyl 16 kV/mm (min.); polyolefin 22 kV/mm (min.), both ASTM D149 |
| Certification | UL Certified, File No. E335936 — printed on the vinyl sheet only |
| Manufacturer's test basis | ANSI C37.20.2, the manufacturer's stated test basis for MV switchgear to 36 kV |
| Re-entry | Supplied complete with fasteners; installed, removed or replaced in a few minutes |
| Qualification reports | QR 1018 (vinyl), QR 1031 (polyolefin) |
Why the part is a shell and not a tube
A finished connection has no single diameter to order against. A round riser landing on a flat plate, an elbow turning behind a current transformer, a tee with four fastener heads on its underside — each is a shape, and the moulding has to be drawn to that shape or it will not close. This is why the enquiry that gets answered fastest carries a sketch rather than a rating, and why two identical-looking joints in the same cubicle can take two different parts.
The second reason is the one that shows up two years later. Thermographic scans, a re-torque interval, a connection somebody already knows will be altered: all of them mean the cover has to come off and go back on without a knife and without a replacement part on the shelf. Both sheets describe the shroud as installed, removed or replaced in a few minutes, and the vinyl sheet adds that it is supplied complete with its fasteners. Nothing else in this class of product publishes that as a property.
Where the two halves of the shell meet, the vinyl sheet describes an overlapping design and claims additional protection against flash-over at the closure. That is the seam a fitter will be looking at, so it is worth knowing the manufacturer treats it as a feature rather than a tolerance.
Minimum wall against voltage class, both materials
Read down your voltage class first, then across. The two ladders do not end at the same number: the vinyl table runs to 38.0 kV, the polyolefin table stops at 36.0 kV, and 36 kV is the ceiling both sheets give for the part itself in prose. The vinyl column is headed recommended; the polyolefin column is headed minimum. Those are not the same instruction, and a wall thicker than its row still satisfies a minimum.
| Voltage class | Vinyl (PVC) | Cross-linked polyolefin |
|---|---|---|
| 3.3 kV | 1.25 mm | No row published |
| 12.0 kV | 2.00 mm | 1.0 mm |
| 18.0 kV | 2.50 mm | 1.4 mm |
| 24.0 kV | 3.00 mm | 1.8 mm |
| 36.0 kV | No row published | 2.5 mm |
| 38.0 kV | 4.50 mm | No row published |
The rows that actually choose the material
Voltage cannot decide this, because both constructions are published against the same 36 kV connection ceiling. These are the measured differences, each with the method it was measured by.
| Property | Vinyl (PVC) | Cross-linked polyolefin | Test method |
|---|---|---|---|
| Dielectric strength | 16 kV/mm (min.) | 22 kV/mm (min.) | ASTM D149 |
| Continuous operating temperature | −20 °C to 115 °C | −40 °C to +115 °C | IEC 216 |
| Hardness | 65 ± 5 Shore A | 45 ± 10 Shore D | ASTM D2240 |
| Tensile strength | 12 N/mm² (min.) | 9 N/mm² (min.) | ASTM D638 |
| Elongation | 350% (min.) | 300% (min.) | ASTM D638 |
| Water absorption | 0.5% (max.) | 0.5% (max.) | ASTM D570 |
| Density | 1.23 gm/cm³ | No row published | ASTM D792 |
| Volume resistivity | No row published | 1 × 10¹³ Ω·cm (min.) | ASTM D257 |
| Flammability | Pass | No row published | UL 94-V0 |
| Halogen content | Not stated | Halogen free | — |
Four polyolefin rows that are on the web page and not in the PDF
| Test description | Recorded value | Test method |
|---|---|---|
| Accelerated ageing | Pass | ASTM D2671 |
| Tensile strength, listed under Thermal | 10 N/mm² (min.) | ASTM D638 |
| Ultimate elongation, listed under Thermal | 250% (min.) | ASTM D638 |
| Resistance to track and erosion | No tracking, erosion or flame failure up to 3.25 kV for 20 min | ASTM D2303 |
The manufacturer's polyolefin product page carries these under its thermal and electrical headings; the extracted PDF of the same product does not. The same page also lists a shrink temperature of 125 °C (IEC 216) — a moulded shroud is not shrunk onto anything, so get that row confirmed before it is used for a process temperature.
Not published: no ordering codes, no dimensions
Neither sheet carries a selection chart. The vinyl sheet's drawing page numbers sixteen connection shapes, TYPE 01 to TYPE 16, and prints no dimension beside any of them; the polyolefin sheet shows a single drawing marked TYPE 02, next to a caption about a tool for button fitting. So there is no code to look up and no table that turns a joint into a part number — the type number narrows the shape and nothing more. What the manufacturer works from is geometry: the type reference if one of the sixteen matches, otherwise a dimensioned sketch or a photograph with a rule laid across the joint. Ask for the drawing before assuming a standard part exists for your connection.
Two flexible PVC ladders, and they are not interchangeable
The same manufacturer publishes a second flexible PVC shroud — Insulshroud, aimed at wildlife-caused outages on outdoor assets rather than at panel connections — and its numbers are not the ones above. Insulshroud is recommended at 2.20 mm for 12 kV, 3.10 mm for 18 kV, 3.80 mm for 24 kV and 5.50 mm for 38 kV, at a dielectric strength of 12 kV/mm (min., ASTM D149) and a continuous operating temperature of −40 °C to 115 °C (IEC 216). Every one of those walls is thicker than the corresponding vinyl connection-shroud row, and the dielectric figure is 4 kV/mm lower. Both sheets say specially formulated polyvinyl chloride, both carry UL File No. E335936, and the material name therefore tells you nothing about which ladder you are reading. Both are printed here because both are published; the one that governs a panel connection is the vinyl ladder in the table above. The outdoor range has its own page on wildlife protection covers.
Custom moulding, and what the sheet actually promises
Most cubicles contain at least one connection that matches nothing in a catalogue. Four published statements decide whether that is a problem or a line item.
- A new design mould is developed within a week. The vinyl sheet prints that beside its offer of customised design for any shape or connection. It is a tooling time. It is not a delivery date, and no delivery date is published anywhere on either sheet — do not read one into it.
- Tooling cost is a fraction of injection moulding. The sheet never names the process it uses instead, but it claims two consequences: no internal stress moulded into the parts, and large parts made without significant tooling investment. For a one-off geometry it is the difference between a quoted moulding and a taped joint.
- Design assistance and CAD drawings are offered. The manufacturer's Insulshroud sheet is where that is stated, beside an in-house tool and die shop, an in-house compounding laboratory, and electrical testing rigs reaching 50 kV under the manufacturer's own roof.
- Ask how the moulding closes before you order it. The vinyl sheet says complete with fasteners; the polyolefin sheet captions a drawing as a tool for button fitting. Those are two different closures, and only one of them opens at the panel with what is already in the toolbox.
Where to go next
- Shrouding a switchgear panel or a transformer terminal boxThe five exposure points in one cubicle, and which part closes each of them.
- Fitting covers, shrouds and capsThe removal procedure, which is the half of the job this product is bought for.
- Shroud, boot, cover-up, cap or guardWhen the specification and the supplier are using different words for the same shell.
- Insulator covers and outdoor connection cover-upsThe GPFIC range, for anything mounted outdoors on a structure.
- How to read an insulating cover datasheetWhat each bracketed method above is claiming, and which figures never compare across materials.
- The vinyl shroud on the manufacturer's own siteGala Thermo Shrink Pvt. Ltd., Mumbai, who mould this range and hold UL File E335936.
- The halogen-free polyolefin versionThe same manufacturer's second construction, with the 22 kV/mm figure on it.
- The same publisher's sleeving reference — busbarsleeves.comWhere this shroud family is indexed by connection type, alongside the sleeving this site does not cover.
What this does not do
A shroud does not make the connection touch-safe. There is no touch-proof rating on either sheet, no test on either sheet that puts a probe against a fitted part, and nothing about the shell that alters what is underneath it: a 12 kV joint under 2.00 mm of vinyl is still a 12 kV joint. Taking one off is a live-working decision, and this page is not part of it. The few minutes the datasheet describes is the mechanics of undoing fasteners, not a statement about the state of the circuit while somebody does it — dead, earthed, permit, and who holds it are settled by the site's own procedure and never by a supplier's web page. It hides the joint from your camera. An infrared scan reads the surface of the moulding, not the metal inside it, so every covered connection becomes an opened connection at inspection time; count those points before covering all of them. It publishes no ingress protection rating. Neither sheet carries an IP figure, so nothing here supports a dust or water claim at the connection, indoors or out. And it is not a fix for a joint that was made badly. A shroud that fits well enough to cover a loose bolt covers a loose bolt.
Send the shape, not the rating
A dimensioned sketch or a photograph with a rule across the joint, the voltage class, how many identical connections there are, and whether the joint reopens at every shutdown. Four inputs return a moulding. A voltage class on its own returns another email.