"Insulation" describes a job, not a material property. A label that insulates a 24 V control wire and one that insulates a switchgear busbar can be made from the same polymer, and the word on the box will be identical. What separates them is two numbers — the withstand voltage the application demands and the temperature class it has to survive — and neither appears in the word "insulation". This guide sets out both, explains why thickness is an output rather than an input, and gives a table for matching the two numbers to the equipment.
1. Two numbers, not one word
- Withstand voltage. The potential the insulation has to hold off, in the conditions of the application. It is an absolute figure for the assembled label, not a material constant.
- Temperature class. The continuous temperature the construction is expected to live at. Electrical insulation classes are a long-established ladder — commonly 130 °C, 155 °C and 180 °C — and a label has to sit on the same rung as the equipment it marks.
- They move independently. A construction can hold a high voltage and have a modest temperature limit, or the reverse. Ask for both.
Neither number is in the word "insulation", which is why a request written only that way cannot be quoted precisely.
2. Why thickness is an output, not an input
Dielectric strength is normally quoted per unit thickness — kilovolts per millimetre — and that figure is not constant across the range.
- Absolute withstand is strength times thickness. Double the film and you roughly double the voltage it holds, which is how the same polymer can serve a control circuit and a busbar.
- Thin films often show a higher figure per millimetre. The headline number flatters thin gauges, while the absolute volts they hold are lower. Quoting the per-millimetre figure alone hides this.
- Geometry counts as much as the material. A label too small for the voltage can be tracked around its edge, and an air gap under it can allow partial discharge. Creepage distance over the surface is part of the design.
So the specification runs the other way round: state the voltage the circuit works at, add the margin your standard requires, and the thickness follows from that.
3. Choosing by equipment
| Equipment | Withstand voltage to ask for | Temperature class | Material | Thickness reference |
|---|---|---|---|---|
| Motor nameplate and lead marking | the motor circuit's rated voltage plus the margin in your standard | 130–155 °C, higher close to the winding | PET, or PI near the winding | 25–50 µm |
| Transformer and coil marking | set by the winding insulation, not by the label | 155–180 °C | PI | 25–75 µm |
| Switchgear and busbar | the highest of the group — kV-class clearances | 130–155 °C | PET or PI | 50–125 µm |
| Wire and cable harness | the cable's own rating sets the bar | follows the cable's class | PVC or PET | 25–50 µm |
| Power module | moderate, but the working voltage is not the whole story | 180 °C class | PI | 25–50 µm |
Ranges are given rather than single figures because the answer depends on the equipment's own insulation system and on the standard the assembly is assessed against. Where the binding constraint is temperature rather than voltage, high-temperature labels covers that side; where the equipment also has to satisfy a flammability requirement, flame-retardant labels is a separate question. PI appears in both discussions: PI film labels covers it as a material.
4. Where insulation specifications go wrong
- Buying "insulation" without a voltage. The word appears on products spanning several orders of magnitude of withstand.
- Quoting a per-millimetre figure as if it were the label's rating. That is a material property; the label's rating is an absolute value.
- Forgetting the adhesive. The construction is facestock plus adhesive. An insulative film on an adhesive that is not insulative gives an assembly that is not what was specified.
- Assuming the label must carry the equipment's class. It has to survive the same environment, not necessarily bear the same designation.
FAQ
How do I know what thickness I need?
Work backwards. State the circuit voltage, add the margin the applicable standard requires, and the thickness follows. Choosing a thickness first and checking the voltage afterwards is how assemblies end up marginal.
Is PI always the right choice for insulation?
No. PI earns its cost where the temperature is high. For a control circuit at ordinary temperatures, a PET construction usually does the same job for less.
Does the adhesive matter for insulation?
Yes. The adhesive is part of the construction, and the assembled label's performance is what the equipment sees.
Is an insulating label the same as an anti-static one?
They are opposite requirements. Insulation wants charge to stay put; anti-static control wants it to drain. A construction specified for one is not suitable for the other.
Browse the range
Start from the functional labels group, which covers insulation together with waterproof, cold-resistant, flame-retardant, anti-static and anti-counterfeit options. Send the circuit voltage, the temperature the equipment runs at and the standard the assembly is assessed against, and a construction can be matched before samples are issued.