Why is the type of insulation and its thickness important?
Voltage is the electrical equivalent of pressure – the harder the power is “pushed”, the further it can travel. As the voltage is increased, a bigger barrier is required to stop the electricity “jumping” across to earth. This is done by increasing the insulation thickness around a conductor.
Take this illustration of the nominal insulation thicknesses on different voltage cables:
The dielectric strength of the material also impacts the insulation thickness. Dielectric strength is the maximum electrical field that the material can withstand - under ideal conditions - without undergoing electrical breakdown and becoming electrically conductive. In terms of insulators and insulation materials, the higher the dielectric strength the better it is.
It also then holds true that if a material has a better dielectric strength, you will need less of it to withstand the electrical field compared to a material with a lower dielectric strength. This means that the choice of insulation material can have a direct impact on the overall diameter of the cable. This can be important when severe space restrictions are present in the installation design - as is often the case. Similarly, less insulation material being used can have a small positive impact on the sustainability profile.
The most common insulation materials are Cross-linked Polyethylene (XLPE) and Ethylene Propylene Rubber (EPR) - with Polyvinyl Chloride (PVC) also used in some low voltage cables. This is how they compare:
| Conductor Size | IEC 60502-1 | EN 50525-3-21 | ||
|---|---|---|---|---|
| XLPE | PVC | EPR | EI8 | |
| 1.5mm2 | 0.7mm | 0.8mm | 1.0mm | 0.8mm |
| 400mm2 | 2.0mm | 2.6mm | 2.6mm | 2.8mm |
So as you can see, for low voltage power cables manufactured in accordance with IEC 60502-1, where XLPE insulation is specified, its better dielectric strength means a thinner nominal insulation thickness at the same voltage rating than other common dielectrics.
Looking at cable standard EN 50525-3-21 - for cables at 450/750V such as the H07ZZ-F LSZH Rubber flexible cable, the specification of EI8 material (XLOHLS - Cross-linked zero halogen low smoke), even at a reduced voltage rating, sees the insulation thickness significantly increased, resulting in larger overall diameters than a comparable size N2XH Class 5 flexible cable at 0.6/1kV.
When this is then amplified by the laying of multiple cables, this can have a big impact.
| Cores x Conductor Size | Cable Type | Overall Diameter |
|---|---|---|
| 4x 240mm2 | N2XH Flex 0.6/1kV (Cu/XLPE/LSZH) | 61.5mm |
| 4x 240mm2 | H07ZZ-F 450/750V (Cu/EI8/LSZH) | 81.5mm |
For more support in specification and insulation materials, please speak to our technical team.
People also ask
XLPE or Cross-linked polyethylene is a thermoset insulation material. Crosslinking polymers is a process which changes the molecular structure ...
Ethylene Propylene Rubber is a generic term for a wide range of polymers based on copolymers of ethylene and propylene...
PVC (Polyvinyl chloride) is widely used in electrical cable construction for insulation, bedding and sheathing. It was the 1950s when PVC...
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