Dielectric breakdown – when does insulation stop working?
Dielectric breakdown – when does insulation stop working?Date of publication: 21-07-2026 🕒 5 min read
Dielectric breakdown is a phenomenon in which the insulating material loses its properties and begins to conduct electric current. It occurs when the permissible dielectric strength is exceeded, that is, the critical electric field intensity for a given material.
This phenomenon is crucial in engineering practice – it is responsible both for natural atmospheric discharges and for failures of electrical devices, installations, or electronic systems. Understanding the mechanisms of breakdown and the factors influencing it is essential for designing safe and reliable systems.
What is a dielectric?
A dielectric is a material with very low electrical conductivity, which normally does not conduct current. In its structure, electrons are strongly bound to atoms, so they cannot move freely under the influence of an electric field.
In practice, this means that dielectrics serve as electrical insulators, separating elements at different potentials and preventing uncontrolled current flow.
The most commonly used dielectrics include:
- gases (e.g., air),
- liquids (e.g., transformer oils),
- solids (e.g., glass, ceramics, plastics).
A key parameter of every dielectric is its dielectric strength, i.e., the maximum electric field intensity that the material can withstand without losing its insulating properties.
where:
- E – electric field intensity
- U – voltage
- d – insulation thickness
Importantly, this formula is a simplified model that does not account for many factors such as material defects, aging, or moisture.
What is dielectric breakdown?
Dielectric breakdown is a phenomenon in which the insulating material loses its properties and starts conducting electric current. It occurs when the critical electric field intensity for the material—that is, its dielectric strength—is exceeded.
At the physical level, this process is associated with a rapid increase in the number of charge carriers. In gases, this takes the form of ionization, whereas in solids it may result from electron breakdown, thermal effects, or degradation of the material’s structure.
The effects of breakdown depend on the type of dielectric and operating conditions. Two basic cases are distinguished in practice:
Reversible breakdown
Occurs mainly in gases (e.g., in air). After the electric field subsides, the ionized particles recombine, and the material returns to its insulating state.
Irreversible breakdown
Characteristic of most solids. It leads to permanent damage to the material—melting, carbonization, or cracking. As a result, the insulator loses its properties and is no longer fit for use.
Examples and symptoms of dielectric breakdown
The phenomenon of dielectric breakdown manifests very concretely in practice—from visible electrical discharges to hidden damage to components and insulation. Depending on the medium and operating conditions, it can take various forms.
Electric arc in air
One of the most characteristic symptoms is a spark jump between conductors. This occurs when the air ionizes and forms a conductive channel. This phenomenon is observed, among other things, as atmospheric discharges.
Damage to wire insulation
Breakdown of insulation in electrical installations leads to short circuits or the appearance of voltage on device housings. This poses a direct risk of electric shock and fire hazard.
Destruction of capacitors
In capacitors, dielectric breakdown causes a short circuit between the plates. In power components, this may lead to sudden damage or even explosion.
Arcing on printed circuit boards (PCBs)
In electronic circuits, too small gaps between tracks may cause electric arc overjump (so-called flashover). Key parameters here are clearance (gap in air) and creepage (surface leakage path on the insulator).
What does dielectric strength depend on?
Dielectric strength is not a fixed value and depends on many material and environmental factors. In practice, this means that the same material may behave differently under different operating conditions.
The most important factors are:
Type of material
Each dielectric has a different structure and physical properties that directly affect its resistance to breakdown. For example, air’s strength is about 3kV/mm, plastics range 10–30kV/mm, and specialized ceramic materials can exceed 100kV/mm.
Insulation thickness
As thickness increases, the overall insulation resistance to breakdown increases, although this relationship is not perfectly linear and depends on material quality and uniformity.
Humidity and contamination
The presence of moisture, dust, or salts significantly reduces insulation strength. Surface contamination can create conductive paths that shorten the leakage route (creepage) and ease current flow.
Duration of voltage application
Long-term exposure to electric fields leads to gradual material degradation (so-called dielectric aging). Conversely, short transient overvoltages may cause breakdown despite normal operation under nominal conditions.
How to prevent dielectric breakdown?
Preventing dielectric breakdown is one of the key aspects of designing electrical and electronic systems. It requires consideration of both material properties and operating conditions as well as the geometry of the entire system.
Insulation design
The foundation is the proper selection of insulating material according to operating voltage and possible overvoltages. Both nominal conditions and short-term overloads, such as switching surges or atmospheric discharges, must be considered. Maintaining appropriate insulation distances according to standards (e.g., IPC-2221) is critical. In practice, distinctions are made between:
- clearance – minimum distance in air,
- creepage – leakage path along the insulator’s surface.
In many applications, additional insulation layers such as heat shrink tubes, spacers, or ceramic shields are used.
Circuit construction
The geometry of conductive elements significantly influences the distribution of the electric field. Sharp edges and points where local field intensity increases are especially hazardous.
Approximately, this relationship can be described as inversely proportional to the radius of curvature (the sharper the edge, the greater the local electric field, increasing the risk of breakdown).
Therefore, design guidelines include:
- avoiding sharp endings of tracks and components,
- maintaining appropriate distances between conductors,
- exercising particular caution in high-voltage systems.
For elevated voltages, additional shielding and suitable insulating housings are also employed.
Protection against environmental conditions
Environmental factors can significantly reduce dielectric strength. Moisture, dust, and industrial contaminants promote leakage currents and increase breakdown risk.
In practice, measures include:
- conformal coating (varnishing of PCB boards),
- system hermetization,
- materials with increased resistance to creepage,
- hydrophobic coatings (e.g., silicone-based).
Equally important is maintaining cleanliness and dryness inside devices, especially in environments with elevated humidity or dust levels.
Where can dielectric breakdown pose a threat?
The risk of dielectric breakdown exists in every electrical system, but in some applications its consequences may be particularly dangerous for both devices and users.
Power supplies and high-voltage systems
This applies to devices powered from a 230V AC network as well as specialized high-voltage converters. Insulation breakdown usually results in short circuits and permanent component damage.
Power capacitors
These components store significant energy. Dielectric breakdown causes rapid discharge, which may damage or rupture the casing.
Wires and electrical installations
Insulation damage is one of the most common causes of failures and fires. The risk increases with overloads, overheating, or mechanical cable damage.
Measurement and laboratory systems
Incorrect selection of probes or measurement cables can lead to exceeding their dielectric strength. In such cases, current may flow along unintended paths, posing hazards to the operator.
Summary
Analysis of the dielectric breakdown phenomenon leads to a very important conclusion for engineering practice – insulation is never a fixed state but a highly sensitive, dynamic balance of physical, chemical, and environmental forces.
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