Installing a busbar sleeve: measure, cut, shrink, inspect
One temperature, 125 °C, and eight steps — five of which finish before any heat reaches the bar.
Before anything else
The bar is dead: isolated, proved dead, earthed, and the panel released to the crew. Heat comes from a gas torch or a hot air gun — the two site methods the manufacturer publishes for its heat-shrinkable bus sheet. An open flame inside a switchgear enclosure is a permit-to-work matter, not an installation tip.
The sequence
Recovery is permanent, so the order matters more than the pace. What the manufacturer publishes about a sleeve going onto a bar is three things: the size bands, the shrink temperature, and the heat source. There is no published installation procedure for BUSTUBE, so the handling below is ordinary heat-shrink practice built around those three figures, and it is flagged where the distinction matters.
Measure width plus breadth, not width
Rectangular bar is specified on W+B — width and breadth added — because that sum is what the tube passes over and then closes onto. A 100 × 10 mm bar is W+B 110, which sits inside the GMB 120/45 band of 104–150 and the GHB 120/45 band of 94–125. Round bar is specified on diameter. Measure the bar as it will sit, including any packing the sleeve has to travel across.
Take the grade from the voltage, the size from the band
Grade is set by system voltage: GSC thin wall to 3.3 kV, GMB medium wall to 24 kV, GHB heavy wall to 36 kV, all non-tracking cross-linked polyolefin meeting ANSI C37.20.2. Inside the grade you read the W+B or diameter band on the row, not the supplied diameter. Each row also publishes supplied diameter D, recovered diameter d and recovered wall T at ±10 per cent. Bands and reel lengths are on the size chart.
Deburr and clean the bar
Take the sharp edge off drilled holes and off every cut end the sleeve travels over — a closing wall has to fold around whatever is under it. Clear swarf, jointing compound and grease off the flats and the corners, and let the bar dry before heat goes near it.
Cut with an allowance, on the bench
Cut longer than the clear bar length so the run laps onto whatever insulation it meets at each end. The only allowance figure published anywhere in this range is written for bus sheet at a joint: 100 mm minimum onto each leg before shrinking, 65 mm of overlap after. Nothing equivalent exists for a straight sleeve run, so that overlap comes off the panel drawing rather than off a datasheet.
Position before the joint is made up
A tube goes on over an open bar end and nowhere else. Once a tee or a bolted lap is assembled nothing gets past it, and a recovered sleeve does not move at all. Slide every length on first, park them clear of the joint faces, then bolt up.
Bring it to 125 °C, evenly, all the way round
125 °C is the published shrink temperature. The material recovers towards the profile it was moulded in, closing to diameter d and reaching wall T. Work from one end so the shrink front drives air ahead of it, and carry the heat around all four flats and both corners instead of parking it on the face nearest you. Polyolefin scorches well before the copper under it is warm, so the gun or the flame keeps moving.
Verify the recovery
A recovered sleeve follows the bar: down onto both corners, corner radius visible through the wall, no turn or slide under hand pressure. Sight along the run at a low angle — an unrecovered stretch reads as a straight line bridging a corner instead of wrapping it. A closed wall is also what seals the bar against the acid, alkali and salt the manufacturer lists this material as protecting against; a half-recovered edge seals nothing.
Inspect, then record the code
Walk the run for the four defects below, then write grade and size code against that bar on the as-built. Replacement means cutting a sleeve off rather than sliding it off, so that record is what stops the next crew measuring the bar again through a wall.
Marking, and what recovery does to it
A GHB 100/38 sleeve goes on at 100 mm supplied diameter and closes to 38 mm. Its circumference finishes at 38 per cent of what it started at, and anything sitting on the surface travels with the wall. Identification is therefore a step-4 decision, not a step-8 one.
Colour carried in the material survives, because there is nothing on the surface to distort. Applied markers, printed film and wrap-on tags are not published as recovery-proof. Mark after the wall has closed, or order stock that is coloured through.
Identification that has to survive a refit belongs on the removable parts. A BUSBOOT shroud over a joint and a BUSCAP over a bar end both install, remove and replace in minutes, so their marking comes off with the part and goes back on with it. Which colour carries which phase is fixed by the project drawing set and the local wiring rules, not by the sleeve.
Four defects, and how each one reads
No defect catalogue is published for this product, so these are the four worth naming on a walk-round and what each looks like from a metre away. Deterioration that arrives later belongs to how busbar insulation fails in service.
- Trapped air. A soft blister, or a run of them, on the face the heat reached last and often over a drilled hole. The wall is not touching the bar there, so the insulated clearance the grade was chosen for is not present along that stretch. Reheat and work it towards the nearest cut end; if it will not travel, cut the section out.
- Incomplete recovery at an edge. The sleeve bridges a corner in a straight line instead of following the radius, or the last stretch sits near supplied diameter D because the heat ran out before the run did. Cheapest of the four to put right: more heat, carried around the bar rather than along it.
- Scorch or thinning. A gloss change, a brown edge, or a length measurably under nominal T — and T is tolerated only to ±10 per cent. The heat source dwelt. Scorched polyolefin does not come back with more heat, so that length is cut out and renewed.
- Longitudinal split at a corner. A line opening along the bar's edge, either during recovery or afterwards as the assembly settles. It does not stay the length it started. Replace it, and find what the wall was folding over before the replacement goes on.
Where the sleeve is the wrong part
The sleeve is a straight-run part. Six geometries decide whether the job stays a sleeve job; the full set of shapes is on busbar connections.
| Geometry on the bar | Heat-shrink sleeve | Removable shroud, sheet or cap |
|---|---|---|
| Straight run between supports | The intended case. One cut, one pass of heat. | Not required. |
| Bend or angled bar | Published as flexible enough for angled bars without creasing. | Not required unless the bend carries a bolted joint. |
| Bolted tee or elbow | Cannot be slid on once the joint is made up. | BUSBOOT is moulded for tees and elbows and ships complete with fasteners. |
| Joint that gets torque-checked | Has to be cut off to reach the bolts, then renewed. | A shroud comes off and goes back on in minutes, as often as required. |
| Irregular or oversize joint | No size code fits a shape that is not a bar. | GHHS bus sheet is cut to the joint: 100 mm minimum onto each leg, 65 mm overlap after shrinking. |
| Live bar end | A tube covers the flats and the corners, not the end face. | BUSCAP covers the end face and is made to be removed and refitted. |
Questions that come up on the bench
What temperature does a busbar sleeve recover at?
Gas torch or hot air gun?
Can a sleeve be recovered on a live bar?
Can a recovered sleeve be slid along or re-used?
How much does insulating the bar change the clearance?
Where this leads
- Busbar sleeve size chart — GSC, GMB and GHBW+B and diameter bands, D, d and T, and reel length by size code across all three grades.
- The sleeve itselfWhat the part is, what it is tested to, and where the 36 kV ceiling actually sits.
- How busbar insulation fails in serviceTracking, ageing and mechanical damage — what a walk-round on the day cannot predict.
- The standards a busbar sleeve is tested toFootnote to this page: IEC 216 is the source of the 125 °C shrink and −40 °C to +115 °C service figures above, and ANSI C37.20.2 is the switchgear application standard behind the grade split.
Send the bar section and the voltage
What this procedure does not establish. A clean recovery is a mechanical result. No withstand figure follows from a sleeve that closed down neatly, and colour is not proof of phase: neither this sequence nor a marker applied during it is a dielectric test or an identification record. What a message can settle is the part — send bar width and breadth, run length, system voltage and the number of bolted joints, and the grade and size code come back read off the chart.