Bus sheet · GMHS and GHHS
Heat-shrinkable bus sheet, GMHS and GHHS
Cut it a minimum of 100 mm onto each leg, shrink it with a torch, then check 65 mm of overlap onto the insulation already there. That is the method for a joint where tubing and tape cannot be used.
Bus Sheet, GMHS and GHHS grades
An adhesive-coated sheet of non-tracking cross-linked polyolefin, cut on site to the joint in front of it and shrunk down with a gas torch or a hot air gun. The manufacturer catalogues it as a high voltage insulation sheet. On a panel drawing it is the part that takes the tees, elbows and connection shapes nothing catalogued fits.
- Cut from flat stock, so the geometry does not have to exist as a moulding first
- 1.5 mm adhesive layer — 4 mm of sheet, 5.5 mm as supplied
- Halogen free and flame retardant
- Three 450 × 325 mm cuts, one 100 mm tee each, out of a single GHHS sheet
| Material | Non-tracking cross-linked polyolefin, adhesive coated |
|---|---|
| GMHS grade | Flashover protection to 17.5 kV |
| GHHS grade | Flashover protection to 36 kV |
| Standard | ANSI C37.20.2, medium-voltage switchgear application |
| GHHS sheet as supplied | 1200 × 430 mm |
| Thickness | 4 mm; 5.5 mm including the 1.5 mm adhesive layer |
| Installed with | Gas torch or hot air gun; no mould, no special tool |
Cutting a bus sheet to a joint
The cut is the part, and its two governing figures are taken at different moments: the 100 mm allowance on the flat sheet, the 65 mm overlap on the finished cover.
Add 100 mm to every leg
Size the cut so it extends a minimum of 100 mm onto each leg, beyond the connection itself. Nothing here is measured on the shrunk cover.
Set the cut size, then work the yield
A 100 mm busbar tee takes a 450 × 325 mm cut. One 1200 × 430 mm GHHS sheet gives three cuts of that size, which is the number to order against when a panel carries a run of identical tees.
Wrap the joint
Wrap the cut round the connection and position it to land on the insulation already on each leg rather than short of it.
Shrink it down
Apply heat with a gas torch or a hot air gun until the sheet has conformed tightly to the joint. No mould and no special tool is involved.
Check 65 mm of overlap
The cover must overlap the existing insulation by 65 mm, and that figure is specified after shrinking.
GMHS to 17.5 kV, GHHS to 36 kV
Grade is the only voltage decision on this part. GMHS gives flashover protection to 17.5 kV and GHHS to 36 kV. Both are the same non-tracking cross-linked polyolefin, halogen free and flame retardant, and both meet ANSI C37.20.2 for medium-voltage switchgear application up to 36 kV.
The sheet range ends at GHHS. Above 36 kV the busbar part in this range is the GEHB series at 66 kV — a sleeve for a straight run, a separate series rather than a higher sheet grade.
What ANSI C37.20.2 asks of a busbar cover is decoded once, on the standards page, rather than restated under every product here.
Sheet or shroud
A moulded BUSBOOT and a cut sheet both close over the same tee. Three things fork the choice.
- Geometry. A sheet is cut on site to the shape in front of it. A shroud has to exist as a moulding in that shape first — the manufacturer catalogues the standard connections and states a week to tool a new mould, and that week is the cost of an unusual joint.
- Tubing and tape have run out. The sheet is specified for joints where tubing and tape cannot be used. A sleeve is catalogued against a bar section, with a minimum and maximum W+B per size on the size chart — and a tee is not a bar section.
- Sealed against refittable. The shroud publishes a removal claim: it installs, removes or replaces in minutes, as often as required, and the PVC version ships complete with its fasteners. The adhesive-coated sheet publishes no such claim. A joint you expect to open again for thermographic inspection or re-torquing takes the shroud.
GHHS sheet format and cut sizes
| Dimension | Figure |
|---|---|
| Sheet as supplied | 1200 × 430 mm |
| Sheet thickness | 4 mm |
| Thickness including adhesive | 5.5 mm |
| Adhesive layer | 1.5 mm |
| Allowance on each leg, before shrinking | 100 mm minimum |
| Overlap onto existing insulation, after shrinking | 65 mm |
| Cut for a 100 mm busbar tee | 450 × 325 mm |
| Cuts of that size per sheet | 3 |
Format figures are published for the GHHS grade. Confirm the GMHS sheet format on the datasheet before cutting.
Figures this page will not give you
The manufacturer publishes no measured property table against the bus sheet: no recorded values, no test-method column. Temperature limits, ingress ratings and weathering figures do circulate for the busbar family, and a value recorded on a moulded shroud or a heat-shrink sleeve is not a value for a 4 mm adhesive-coated sheet. Ask for the sheet's own test report before any of it reaches a specification.
Where the sheet sits in the range
- Seven busbar connection geometriesWhich joint shapes take cut sheet and which take a moulding
- BUSBOOT insulating shroudThe refittable cover, in polyolefin or PVC, both to 36 kV
- Busbar heat-shrink sleeve: GSC, GMB, GHBStraight runs to 3.3, 24 and 36 kV by wall grade
- GBBS barrier board sheetNon-shrinkable polyolefin at 2.0, 3.0 or 5.0 mm — an inter-phase barrier, not a joint cover
- Manufacturer's bus sheet pageGala Thermo Shrink Pvt. Ltd., who make the sheet this page specifies
Send the joint, not the part number
Send the bar section, the leg lengths either side of the connection and the voltage class, and the cut size comes back with the grade. One limit, stated plainly: a sheet seals a joint from the outside and establishes nothing about the joint underneath. Bolt torque, contact area and the temperature rise across the bolted face are busbar design questions, settled before any cover goes on.