Two states of the same bar
Insulated busbar against bare busbar
The covering buys 180 mm of phase spacing at 36 kV. Thirteen aspects, sorted into what that improves, what it makes worse, and what it does not touch at all.
The purchase is 180 mm at 36 kV
Covering a bar does not raise the panel's rating and does not make it safe to work on live. What it moves is the spacing: heavy wall is published at 140 mm phase-to-phase at 36 kV where IEC 71-2 asks 320 mm of air for the same bare copper.
Every other entry below is real, and none of them would carry the line item alone. Buy the width; take the rest as change.
The figures at 12, 17.5, 24 and 36 kV — both wall grades, both conductor shapes, and the phase-to-earth column that turns out to be the binding one — are tabulated under cutting busbar air clearance. This page is the other half of that decision: what the width costs once the panel is in service.
The verdict, aspect by aspect
The direction of travel when a bare bar in an existing design is covered. The rows marked unchanged are the ones most often assumed to move, and they deserve more attention than the rows marked improves.
| Aspect | Verdict | What actually happens |
|---|---|---|
| Enclosure width | Improves | Phase centres fall to the sleeved figure — 140 mm against 320 mm at 36 kV on heavy wall. Section width, bar length and floor area follow them in. |
| Touch safety | Improves | A recovered wall of cross-linked polyolefin sits between the copper and a hand, a dropped spanner or a torch barrel. The bar is still live and still worked dead. |
| Flashover from vermin and debris | Improves | The sleeve is supplied to guard against accidental flashover on straight and angled bars. A covered run and a covered joint remove the two surfaces a rodent or a loose washer can bridge. |
| Corrosive atmosphere | Improves | The material is published as resistant to strong acid, alkali and salt. A covered bar tolerates coastal and process air that etches bare copper. |
| Heat dissipation | Worsens | Heavy wall puts 3.20 to 4.20 mm of polyolefin between the copper and the moving air. No derating factor for a covered conductor is published anywhere in this range. |
| Visual inspection | Worsens | Anything a fitter reads off the metal is behind an opaque wall afterwards. What stays visible is the sleeve's own surface. |
| Thermographic survey | Worsens | A camera measures the surface it can see, and that surface is now the sleeve. Settle how joints will be surveyed while the panel is still a drawing. |
| Repair and modification | Worsens | Recovery happens once, at 125 °C. A sleeve is cut off and replaced, never refitted, so a bar that gets modified is a bar that gets re-sleeved. |
| Cost | Mixed | The covering is a line added to the bill of materials. Against it the manufacturer sets shorter busbar lengths and less sheet metal from the smaller panel — which way the total moves is panel arithmetic, and nothing here prices it. |
| Prospective fault current | Unchanged | Set by the source and the impedance of the network upstream. A dielectric covering carries no current and does not enter that calculation. |
| Force between phases | Rises with the new centres | The force between parallel conductors varies inversely with the gap between them, so a bar taken from 320 mm to 140 mm sees more of it, not less. Supports and framing get rechecked against the spacing the sleeve bought. |
| Joint torque and preparation | Unchanged | The covering goes on after the joint is made and changes nothing about how it was made. Torque, contact area and surface preparation stay where the busbar design put them. |
| The bar's own current rating | Unchanged by specification | No current-carrying figure for a sleeved bar is published in this range. The rating stays whatever the busbar calculation produced, rechecked for the covered condition rather than inherited from it. |
An insulated bar is not a safe-to-touch bar
Touch safety improves in the table above, and that is all it does. Nothing in this range is published as a live-working covering; the parts are qualified for switchgear application, not for contact with a live conductor. Isolate, prove dead, earth. The covering is there for the spanner you drop, not for the hand you put on the bar.
The debit is heat, and nobody publishes it
What the manufacturer publishes are material limits, not conductor ratings. Continuous service runs from −40 °C to +115 °C, with recovery onto the bar at 125 °C. Those describe the polyolefin; none of them says what the copper underneath will run at.
A covered bar sheds heat by conduction through the wall, then by convection from a surface that is larger than the bar and cooler than it. Whether that nets out as a derate depends on section, load current, enclosure ventilation and ambient, and no figure in this range settles it. Do the thermal calculation on the bare bar, then treat the covering as an input to it — never as permission to shrink the section.
The inspection debit is quieter and arrives years later. Two instruments a maintenance team already owns stop reading the joint on the day the bars are sleeved, and what replaces them is a design decision rather than a survey decision. IEC 216, the standard behind the temperature limits above, is decoded with the rest on the standards page.
Recovered or removable is the decision underneath this one
Most of what worsens above belongs to the heat-shrunk sleeve — the manufacturer's BUSTUBE range — rather than to insulation as such. A moulded shroud installs, removes or replaces in minutes, and an end cap is re-usable, so the joints stay reachable while the run stays covered.
Sleeve, shroud and cap are each published as meeting ANSI C37.20.2 for switchgear application to 36 kV, so a mixed build costs no voltage class. A bar that gets torque-checked, surveyed at the joints or modified in service is therefore not an argument for bare copper. It is an argument for a shroud over the joints and a cap on the bar ends.
When bare is still the right answer
Covering a bar is a dimensional purchase. Where there is no dimension to buy, it is a line item with a maintenance penalty attached.
- Open structures already at full clearance. Nothing is recovered where there is no envelope to shrink, and the covering adds a surface that has to be inspected.
- Bars sized on temperature rise, not on spacing. If the section came out of a thermal calculation, the constraint the sleeve relieves was never the binding one, and relieving it moves no dimension on the drawing.
- A reduced clearance the approving authority will not accept. The insulated figures are the manufacturer's, quoted against the bare IEC 71-2 baseline. Whether the standard your panel is signed off to permits an insulation-based reduction is a tender question, and nothing on this site answers it.
- Joints that come apart on a torque schedule. Sleeve the run and leave the joints under a shroud that lifts off: copper you can still reach, under a cover, rather than copper in open air.
- Thin wall mistaken for spacing. The published clearance table carries medium-wall and heavy-wall columns only. GSC is a 3.3 kV grade specified for covering, so fitting it and then closing the phase centres is the one error on this page that ends at a flashover.
- Temporary and test connections. Recovery is one-shot, so a bar that comes down again is not worth a sleeve; tape or a lift-off cover survives being taken off.
Where this decision goes next
- Cutting busbar air clearance with insulationThe 12 to 36 kV table behind the width claim, both wall grades and both conductor shapes.
- The sleeve that shrinks onto the barGSC, GMB and GHB against 3.3, 24 and 36 kV, with the measured properties in a table.
- Busbar sleeve size chartWhich code fits a 100 x 10 mm bar, once the covering is agreed in principle.
- How busbar insulation fails in serviceThe maintenance case behind the inspection debit, and what a distorted sleeve is telling you.
- Busbar insulator or busbar insulation?The supports that move when the phase centres do, and why they are a separate purchase.
- Panels, bus ducts and transformer terminal boxesWhere covered and bare metal end up in one assembly, and the order they get fitted in.
Send the bar section, the voltage and the width you have
Whether covering the bar earns its place is answerable from four facts: bar width and breadth in millimetres, system voltage, the clearance standard the panel is signed off to, and the enclosure width you are working to. Send those four and the grade follows. Standard range datasheet: heat-shrink-busbar-tubes.pdf.
Stated limit
This page compares two conditions of one bar and sizes neither. Derating a covered conductor is a thermal calculation over section, current, ventilation, ambient and duty cycle, and nothing published behind this site performs one.
The improvements listed are the manufacturer's published claims for the covering. The debits follow from putting an opaque wall around something that used to be read by eye. Neither set is a type test of your assembly, and neither replaces the clearance standard the panel is signed off to.