Busbar Heat Shrink Installation: 8.7/15kV–35kV Guide & Anti-Tracking

Busbar heat shrink installation looks like a one-tool job, heat gun, sleeve, done, but the failures we see in MV switchgear track back to four installation details: busbar surface prep, heating profile, edge treatment, and how the casing ends are dressed. This guide walks through busbar heat shrink installation for 8.7/15 kV to 26/35 kV busbars, covering the anti-tracking requirements that turn an installation into a compliant one. It is written for switchgear panel builders, substation contractors and utility maintenance crews installing the WELLELE MPG series or equivalent casing. The product range and voltage selection are on our busbar heat shrink casing page; the reasons for insulating busbars at all are in our Why Insulate MV Busbars guide. The acceptance check at the end doubles as the commissioning record utilities expect from a busbar heat shrink installation.

Before you start: busbar preparation

The casing recovers onto the busbar surface, so the surface decides the result. The three prep steps below are the non-negotiable start of every install:

1. Clean: remove grease, oil and metal dust with a solvent wipe. A fingerprint of oil under the casing becomes a tracking site over time
2. Deburr: break every sharp edge, a burr punctures the wall under recovery, and copper burrs are hard enough to do it reliably
3. Dry: no moisture on the surface before shrinking; trapped moisture flashes to steam inside the casing

Skipping preparation is the most common mistake, and it stays invisible until the first PD test.

Heating method and temperature control

The MPG series recovers at 90–130 °C (MPG10) or 100–135 °C (MPG35), the normal range for an industrial heat gun. Temperature control is the step where operators vary the most:

• Heat evenly along the run, centre outwards, so air escapes ahead of the shrinking front instead of trapping bubbles
• Keep the gun moving: dwelling heats the wall beyond the window and degrades the polymer; the surface should reach recovery temperature without scorching
• Check recovery visually: the casing is fully recovered when it grips the busbar profile with no loose pockets, run a finger along the edges
• Work in sections on long busbars: recover 30–40 cm at a time rather than heating the whole length

The recovery window is wider than it looks, which makes the process forgiving. Overheating one spot for ten seconds still ruins the wall.

Overlap, edges and end treatment

Tracking starts at the edges, so edge treatment is where anti-tracking design does its work:

• Overlap adjacent casing runs by at least the recommended amount (typically 25–50 mm at MV class) so there is no bare busbar between sleeves
• Dress ends square: a torn or angled end exposes the semi-conductive inner layer and becomes a creepage start point
• Stop short of joints: keep the casing back from bolted joints and bimetallic connections so the joint stays inspectable and movement at the joint does not shear the casing
• Corners and bends: on bent busbars, pre-warm the bend area and recover the casing gradually around the radius, forcing it around a sharp bend without heating tears the wall. Edge discipline is what separates a 10-year busbar heat shrink installation from a 2-year one

Copper vs aluminium busbars

• Aluminium expands roughly twice as much per degree as copper, on long runs, allow for movement at the ends and keep the casing clear of expansion zones
• Copper burrs are harder after machining; deburr more aggressively, since a copper edge will puncture a recovering wall more readily than an aluminium one
• Mixed copper-aluminium connections: keep the casing back from the bimetallic joint, and confirm the joint itself is protected by the approved method

Anti-tracking requirements: what makes the installation compliant

Anti-tracking matters more than any other electrical property for busbar insulation, and it is the first thing a compliance audit checks. A tracking path is a conductive carbonised trail that grows across a contaminated surface under voltage. The requirements for an MV-class install are:

• CTI / tracking index: the casing material should carry a published comparative tracking index suited to the pollution level of the environment (dusty, humid, coastal installations need higher CTI)
• PD inception: the semi-conductive inner layer suppresses partial discharge at the casing edges, verify the casing spec includes PD inception voltage (MPG10 > 30 kV/mm, MPG35 > 40 kV/mm), not just dielectric strength
• Creepage distance: where the environment is heavily polluted, extend the casing beyond the minimum clearance to add creepage surface, the casing adds creepage without adding cabinet space
• Flame retardancy: casing for switchgear should be UL 94 V-0

35 kV thick-wall notes

The thick-wall case earns its own notes. At 26/35 kV the MPG35 wall is 3.5 mm or more after recovery, noticeably stiffer than the 2.5 mm MPG10 wall:

• Pre-heat long runs before the final pass so the thick wall recovers evenly
• Allow for stiffness at bends, the thick wall holds its shape; do not expect it to follow sharp radii as freely as a thin wall
• Give the end treatment extra attention: a 35 kV class edge carries more field, so square, clean ends matter even more

Acceptance check after installation

• Visual: full recovery against the busbar profile, no bubbles, no scorch marks
• Edges: square ends, overlap confirmed, casing clear of joints
• Documentation: record the installation (date, operator, casing lot), utilities ask for it at commissioning, and it is the closing step of every documented busbar heat shrink installation

Common questions