Numerous insulation materials are used so that electrotechnical devices and equipment 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. Globally valid standards are necessary for their safe operation. 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 that are operated with a rated voltage of up to 1000 VAC and 1500 VDC. Among other things, minimum clearances and creepage distances are defined and correction factors for use above 2000 m a.s.l. and at increased frequencies.
IEC 62368 Basic standard on safety requirements (especially IT technology)
IEC 62368 applies to electrical and electronic equipment in the field of audio, video, information and telecommunications technology, including electrical office machines up to a nominal 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
IEC 61140 describes the requirements for installations, systems and equipment without voltage limitation in the form of a fundamental standard. Therefore, the specified principles and requirements are kept in such a way that they can be used for the coordination of product-specific standards, i.e. in the form of a reference to this standard. For electrical engineering, the classification of the insulation classes is to be particularly emphasised
Protection class I - III
Pure functional insulation without a protective function against electric shock is not covered by the standard.
I - Fixed connection of all electrically conductive enclosure 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 of electrically conductive enclosure components from live parts. No connection to protective conductor prescribed, if however no connection to conductive, touchable parts.
III - Protection by extra-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. Especially in the presence of moisture and contamination (dust, abrasion, production residues), the surface conductivity can increase to such an extent that a residual 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 higher the CTI value, the worse the material resists degradation in a humid 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 burning test
HB 75 For thicknesses <3 mm; Passed when burn rate < 75 mm/min
HB 40 For thicknesses >3 mm; Passed when burn rate <40 mm/min
Vertikale Brennprüfung
V-2 Extinguishing within 30 seconds, burning dripping permissible
V-1 as V-2, but no burning dripping permitted, no afterglow for more than 60 seconds
V-0 Extinguishing of the flame within 10 seconds, no afterglow for more than 30 seconds
5VB at least V-2 already reached, then 5x flaming with 500 W flame, no dripping allowed
5VA as 5VB, additionally on horizontally clamped panel 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 have to be taken into account in the production of a standard-compliant electrotechnical product. There are numerous product standards 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's electrical insulation products are, among other things, classified according to their Thermal classes, but also subdivided into insulating material classes and have been meeting the requirements from 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