Busbar insulation tape against heat-shrink sleeve

Start with whether the joint comes apart

A busbar sleeve is a continuous tube, cut from a reel and recovered onto the bar at a shrink temperature of 125 °C. It is entered from an open end, so either the bar is threaded before the joint is made or the joint is opened to thread it. Tape is wound onto the bar where it lies and asks for working access and nothing else.

On a panel still on the bench the bars are loose and threading costs nothing. On a panel that is wired, torqued and tested, a sleeve means opening a joint that has already been signed off. Neither material changed between those two cases; the assembly state did.

The second split is where the finished wall comes from. The chart fixes it: GSC walls run 0.69 to 1.50 mm, GMB 1.70 to 3.30 mm and GHB 3.20 to 4.20 mm, each to ±10%, so GMB 100/38 puts 3.00 mm of cross-linked polyolefin on any rectangular bar summing 83 to 126 mm across width and breadth. A wrapped wall is tape thickness times turn count times overlap, and all three are settled at the bar by whoever is holding the roll.

That matters because the published clearance reductions are stated against named wall grades. The manufacturer's table sets a medium-wall and a heavy-wall column beside the uninsulated IEC 71-2 figure — at 36 kV, 140 mm phase to phase on heavy wall against 320 mm bare on rectangular bar. It carries no column for a wrap, so a taped bar has no clearance figure to quote.

Length is the third split and it shows up only at the top of the range. The reel-length column falls from 100 m on GSC 16/8 to 25 m through most of the GMB and GHB series, then to 1.5 m on GMB 205/85, GMB 250/100, GHB 205/85 and GHB 250/120. A long run in a 250 mm-class section therefore arrives in 1.5 m pieces, and the covering itself has joints in it.

When tape is the right call

Each of these is a case where the sleeve is unavailable, not a case where a wrap is the better covering.

• The panel is already bolted up. Threading a sleeve means opening a joint that is already made and already tested.
• The bar has no free end. A run landing on fixed supports at both ends cannot be withdrawn, and a tube has nowhere to start.
• The bar cannot be released for long. That constraint is the reader's own: no installation time is published for either covering, here or in the manufacturer's data.
• A local repair. Where a short length of existing covering is damaged, cutting a whole sleeve off the run is out of proportion to the defect.
• The section is past the chart. The largest rectangular entry published is 314 mm of width plus breadth, on GMB 250/100 and GHB 250/120. Above that there is no size code to read off.

What a wrap gives up

Five of these come out of the published data. The sixth is a working judgement and is marked as one.

• Repeatability. Two fitters produce two walls on identical bars. The chart does not vary that way: GSC 0.69 to 1.50 mm rated to 3.3 kV, GMB 1.70 to 3.30 mm to 24 kV, GHB 3.20 to 4.20 mm to 36 kV, each ±10% and each printed against its size code.
• The clearance argument. Panel width is the commercial reason to insulate a bar at all, and the reduction is published against a named wall grade. A wrap forfeits it.
• Tees and elbows. The manufacturer's bus sheet page places tees, elbows and irregular connections where neither tubing nor tape can be used — that routing is theirs, not an inference drawn here.
• A published overlap figure. The sheet has one: extend a minimum 100 mm onto each leg of the joint before shrinking, and overlap existing insulation by 65 mm after. Nothing equivalent is published for a wrap, and overlap is exactly what sets a wrapped wall.
• Re-usability. It is published for two parts only — BUSBOOT and BUSCAP, both of which install, remove and replace in minutes. It is published for neither the sleeve, the sheet nor a tape.
• Judgement, not a measurement: a shrunk sleeve either conformed to the bar or visibly did not, and an inspector can see which. A wrapped wall can only be checked by measuring it, and a missed lap sits under the next turn.