Numerous insulation materials are used to ensure that electrical equipment and devices can be operated reliably and safely. In the low-voltage range, plastics dominate. To be able to use them safely, you should know the most important standards.
Electrical engineering is one of the areas of industry best regulated by standards. This is no coincidence, since electrotechnical devices are produced, sold and used worldwide. For their safe operation, globally valid standards are necessary. These are provided primarily by the IEC (International Electrotechnical Committee). The following standards are of outstanding importance:
IEC 60664 Insulation coordination for low voltage (Low Voltage Directive)
This very comprehensive basic safety standard defines numerous minimum requirements for devices and equipment operated with a rated voltage of up to 1000 VAC and 1500 VDC. Among other things, it defines minimum clearances and creepage distances to be maintained and correction factors for use above 2000 m a.s.l. and at increased frequencies.
IEC 62368 Basic standard on safety requirements (primarily IT technology)
IEC 62368 applies to electrical and electronic equipment in the field of audio, video, information and telecommunication technology, including electrical office machines up to a rated voltage of 600 V.
As a safety standard with a very comprehensive consideration of all possible risks (electrical, acoustic, mechanical, etc.), many equipment standards refer to this basic standard.
IEC 61140 Protection against electric shock
In the form of a fundamental standard, IEC 61140 describes the requirements for installations, systems and equipment without voltage limitation. Therefore, the specified principles and requirements are kept in such a way that it can be used for the coordination of product-specific standards, i.e. in the form of a reference to this standard. Particularly noteworthy for electrical engineering is the classification of insulation classes
Protection class I - III
The standard does not cover purely functional insulation without a protective function against electric shock.
I - Fixed connection of all electrically conductive housing parts connected to the protective conductor system of the fixed electrical installation (e.g. protective conductor contact).
II - Use of double or reinforced insulation for safe separation even of electrically conductive housing components from live parts. No connection to protective conductor prescribed, if nevertheless no connection to conductive, touchable parts.
III - protection by low voltage, i.e. the use of a voltage below 48VAC/60VDC. Protection class 3 equipment may only be connected to the mains via SELV or PELV power sources.
IEC 60112 Tracking resistance
Plastics have an insulation strength several times better than air. That is why even very thin films can insulate high voltages. However, this insulation strength can deviate greatly at the interface between air and the surface of the insulator. Particularly in the presence of moisture and contamination (dust, abrasion, production residues), the surface conductivity can increase to such an extent that a fault current occurs which, for example, triggers a fuse device (RCD).
In order to classify plastics in terms of their sensitivity to such stresses, the "comparative creep distance index (CTI)" is determined. The greater the CTI value, the worse the material resists degradation in a moist environment.
| Insulating material group | CTI | PTI |
| I | 0 | >600 V |
| II | 1 | 400 - 599 V |
| IIIa | 2 | 250 - 399 V |
| IIIa | 3 | 175 - 249 V |
| IIIb | 4 | 100 - 174 V |
UL94 Flammability (IEC 60695 basic safety standard)
Although there are corresponding fire protection standards in the IEC world, the UL 94 standard is very often used in electrical engineering. This assesses the flammability of plastics and classifies them into seven classes. In addition to the standard thickness of at least 3 mm, identical class designations are used for thinner materials, but with the addition of "TM" for "Thin Material". The test arrangement for thin films is slightly modified.
Horizontal burn test
HB 75 for thicknesses <3 mm; passed if firing rate < 75 mm/min
HB 40 for thicknesses >3 mm; passed if firing rate <40 mm/min
Vertical burning test
V-2 Extinguishing within 30 seconds, burning dripping permitted.
V-1 as V-2, but no burning dripping allowed, no afterglow over 60 seconds
V-0 flame extinguished within 10 seconds, no afterglow over 30 seconds
5VB at least V-2 already reached, then 5x flame application with 500 W flame, no dripping allowed
5VA as 5VB, additionally on horizontally clamped plate no burn hole formation >1 mm.
IEC 60085 Thermal classes (UL 746 similar)
Not every insulation material is suitable for every installation situation. A limiting factor is also the thermal load capacity of the material. IEC 60085 specifies thermal classes for electrical insulation systems and electrical insulation materials within which the materials can be used safely and permanently.
Y 95 °C
A 105 °C
E 120 °C
B 130 °C
F 155 °C
H 180 °C
N 200°C
R 220°C
Of course, these standards are not the only ones that must be taken into account in the production of a standard-compliant electrotechnical product. Numerous product standards exist for electric motors, converters, transformers or electrical fuse devices and electrical cables. However, all of them always refer to the basic standards as well, since these are intended to ensure a generally valid basic protection.
CMC electrical insulation products are classified according to their Heat classesWe have been meeting the requirements of the entire electrical industry for decades. We look forward to your requirements and will almost always be able to offer you a suitable solution.
Six standards of electrical engineering