Busbar insulation is the electrically insulating cover or coating of a busbar. It separates the current-carrying conductor, usually copper or aluminium, from neighbouring bars, the housing and ground. In a battery system or inverter running at 400 or 800 volts, this thin layer decides whether an arc forms between two potentials. At GOBA, busbar insulation runs off the line as a ready-made insulation part: film slit, punched, formed, fitted to the bar.
Function of busbar insulation
A busbar carries high currents in a tight space. Without insulation the designer has to keep large clearances through air, which costs build space. Insulation shrinks these distances because it brings a defined voltage strength of its own. It does three jobs at once: it holds the operating voltage against neighbouring potentials, it protects staff and adjacent parts from contact and short circuit, and it often fixes the position of the bar mechanically. In a high-voltage system, protection against dirt and moisture comes on top, because both shorten the creepage distance across the surface.
Design forms of the insulation
There are three common ways to insulate a busbar, differing in effort, voltage strength and volume.
- Film wrap: the bar is wrapped with a cut insulating film or placed into a blank. Flexible, quickly available, ideal for prototypes and medium series.
- Coating: powder coating, dip coating or overmoulding form a closed layer directly on the conductor. Tight and mechanically robust, but with higher tooling effort.
- Punched and formed part: a pre-shaped insulation part, for example a punched spacer or a deep-drawn frame, sits form-fit at defined points. This is where contract fabrication plays to its strength.
In practice battery makers mix these routes. The continuous bar gets a film wrap, critical contact points and feed-throughs receive an additional punched part. Tight packaging means combining.
Materials for the insulation
The material follows from temperature, the required dielectric strength and the forming the part must survive. These films have proven themselves:
- Polyimide, known as Kapton: around 400 volts per 25 micrometres dielectric strength, continuous temperature up to about 240 degrees. The first choice where it gets hot and tight.
- PET (polyester film, such as Mylar or Hostaphan): affordable, mechanically tough, good insulation values up to around 130 degrees continuous. The standard for many series applications.
- PEN (polyethylene naphthalate): higher temperature range than PET, used where PET no longer holds thermally.
- Composite films: laminates of several layers, for example PET with polyimide or with fleece, combine high voltage strength with mechanical protection. They carry the load a single film cannot hold.
Film thickness is not a free value. It follows from the test voltage, the safety factor and whether the film thins out at an edge during forming. We therefore size the thickness at the weakest point of the formed part, not at the flat web.
Requirements in the high-voltage system
In the 400- and 800-volt system of electric vehicles, the material name alone is not enough. Three quantities decide the design:
- Voltage strength: the insulation must hold the test voltage per standard, not just the operating voltage. A multiple of the nominal voltage is common as the test value. The film's dielectric strength supplies the reserve.
- Creepage and clearance: no leakage current may travel across the surface to a neighbouring potential. Pollution degree and the material group of the film set the required distance. A closed wrap lengthens the creepage path effectively.
- Temperature: the conductor heats up under load. The insulation must withstand the continuous temperature plus reserve without becoming brittle. This is where polyimide parts ways with cheaper PET.
These points interlock with the high-voltage insulation of the whole system and with the cable insulation of the connecting leads. The busbar is only one link in the insulation chain and has to match the rest. In battery packs it often borders the stator insulation of adjacent drive parts and the thermal insulation of the battery cells, where electrical and thermal barriers meet.
Production as a ready-made insulation part
GOBA does not build the insulation piece by piece by hand, but as a repeatable part. The process follows the drawing of the bar.
- The insulating film is slit to the required web width, in assembly to within 0.1 millimetres.
- Contours, feed-throughs and bolt holes are punched, with tooling for the series or tool-free by kiss-cut for samples and small series.
- If needed, the film is formed, folded or laminated so it sits form-fit on the bar.
- Every part is checked for dimension and clean edges, because a burr or a crack at the edge becomes the weak point in the field.
The advantage over hand wrapping lies in repeatability. A punched part sits the same on part 1 as on part 10000, the insulation distance stays constant. That is exactly what quality assurance in the automotive field demands.
GOBA Takeaway
The insulation of a busbar is not an accessory, it is the part that prevents the arc in the high-voltage system. Anyone saving build space while still holding the test voltage cannot avoid polyimide, PET or a composite film in the right cut. GOBA has been slitting, punching and forming these films for decades and delivers busbar insulation as a ready-made part with a constant insulation distance. Send us the drawing of your bar via our page on electromobility and automotive or on insulation and molded parts, and for the pure film cut use battery film slitting. You will receive a technical quote.