Terminology
Busbar insulator or busbar insulation? They are different parts
One bolts to the frame and carries the bar's weight. The other is 0.69 to 4.20 mm of polyolefin on the copper and carries nothing. This site sizes the second only.
Ask what the part is bolted to. A support insulator is bolted to the panel frame and holds the bar up; busbar insulation is shrunk or clipped onto the copper and holds nothing up. If the drawing wants the first, nothing on this site will size it.
The reason to cover a bar is dimensional. IEC 71-2 asks 320 mm phase-to-phase on bare copper at 36 kV, and Heavy Wall sleeve brings the same bar to 140 mm. A support insulator moves neither figure — it holds the bar at whatever spacing the figure demands.
The manufacturer's switchgear insulation index lists busbar sleeve to 36 kV, shrouds in polyolefin and PVC, end caps, Termicap, Bustape, bushing boots and circuit-breaker insulation. No post, no standoff and no bar support appears in it. That part is ordered from a switchgear component supplier, against the frame drawing rather than against the copper.
The collision is in the English. One word covers both a material property and the moulded post built to exploit it, and the two parts share nothing else — not a supplier, not a rating, not a column of a size chart.
The two parts, line by line
Figures in the right-hand column come from the manufacturer's published data. The left column is general switchgear practice: no support insulator appears in any source this site works from, which is why no figure is given for one anywhere on this page.
| Support or standoff insulator | Busbar insulation | |
|---|---|---|
| Also called | Standoff, post insulator, busbar support | Busbar sleeve, BUSTUBE, shroud, bus sheet, end cap |
| What it does | Holds the bar off the frame and off the next phase | Covers the bar so a smaller air gap will do |
| Made of | A rigid body, because it carries load | Cross-linked polyolefin, PVC, or rigid polyolefin board |
| Rated by | Mechanical load, plus a withstand across its own body | Dielectric strength, tracking resistance, temperature limit |
| Sized from | Bar centres, height above the frame, fixing pattern | Bar width plus breadth, against the recovered diameter |
| Fitted | Bolted to the frame before the bar drops in | Shrunk on at 125 C, or bolted over a joint already made |
| If it is absent | Nothing holds the bar in position | Bare-copper clearance applies in full — 320 mm at 36 kV |
| Where it comes from | A switchgear component supplier, not this range | Made by Gala Thermo Shrink Pvt. Ltd. |
Telling the two size charts apart
Both documents look the same from across the desk: a code column on the left, millimetres to the right. The column headings separate them in one look.
A sleeve chart is keyed on the bar. Its columns run Gala size, D in mm minimum, d in mm maximum, wall T at plus or minus 10%, reel length in metres, then rectangular bars as width plus breadth with a round-bar diameter beside it. Reel length is the giveaway — sleeve is cut from a reel and a standoff never is.
A support insulator chart is keyed on the frame instead: an overall height, a thread or bolt size at each end, a load figure. A column asking for a thread size is not a sleeve chart.
On the sleeve chart, add the two bar dimensions before reading anything. A 100 x 10 mm bar enters the width-plus-breadth column at 110 mm, not at 100 mm. Read it as 100 and the Heavy Wall answer looks like GHB 100/38, which in fact stops at 102 mm; at 110 mm the code is GHB 120/45.
The GSC, GMB and GHB chart runs the same bar through all three series, where the answer changes again with the wall grade.
Six words, and which part each one names
- Shroud
- The moulded shell over a bolted joint, off and on in minutes for a torque check — not something a load-carrying part does. BUSBOOT is made in cross-linked polyolefin and in PVC.
- Boot
- American usage for the same shroud. It is also the manufacturer's word for a bushing boot, a separate line in the switchgear index: a part that covers an insulator rather than being one.
- Cover
- A search word, not a part name. The insulation hub maps it onto the five parts that exist.
- Guard
- Points at the board standing in the air gap, never at anything bolted under the bar.
- Barrier
- The manufacturer's name for that board: GBBS, 670 or 970 mm wide and 15 m long, in 2.0, 3.0 and 5.0 mm. Every figure published against it is dielectric or thermal.
- Shield
- A cable word. No busbar part in this range carries the name.
Insulating the bar moves the supports
The two decisions are not independent. Bare copper at 36 kV wants 320 mm phase-to-phase and Heavy Wall sleeve takes the same bar to 140 mm. Move the phase centres to 140 mm and every standoff on that run moves with them — fresh frame drilling, a fresh fixing pattern, and a support insulator selected against bar centres that no longer exist. Settle the sleeve grade and the support layout in one pass. The millimetres are on busbar air clearance.
What gets asked once the distinction lands
Does sleeving the bar let me delete the support insulators?
The barrier board is rigid. Is that a support insulator?
I searched for an insulator and got sleeves. Which do I want?
Can one supplier quote both together?
Where this goes next
- Busbar sleeve size chart — GSC, GMB and GHBEnter it at width plus breadth.
- Cutting busbar air clearance with insulationWhat 320 mm becomes once the bar is covered.
- Five ways to insulate a busbarSleeve, shroud, end cap, bus sheet, barrier board.
- The standards a busbar sleeve is tested toEvery test method on this site, decoded once.
- Insulated busbar against bare busbarThe operational verdict, once the millimetres are agreed.
What this page does not establish
It names which of two parts you want and stops there. No height, no fixing pattern and no load figure for a support insulator is published anywhere on this site, and none will be. Nor does it say anything about the copper underneath: current rating and temperature rise belong to the bar, its cross-section and the enclosure.
Send the bar section, not the part name
Width and breadth in millimetres, the system voltage, and whether the run is straight or jointed. With those three a reply names a size code instead of asking a second question.