Technology / Technical guide
Creepage, Clearance & Wind Converter Insulation Boundaries
Creepage follows an insulating surface; clearance follows a path through air. They can connect the same conductive parts while describing different physical routes and breakdown mechanisms. Neither distance alone establishes the insulation capability of a complete converter.
The path matters as well as its length.
Understand air, surface and solid barriers separately before interpreting a spacing as sufficient electrical isolation.
01 / Two paths
Surface distance and air distance answer different questions.
Clearance is the shortest air path between the relevant conductive parts.
Clearance is the shortest air path between the relevant conductive parts. Creepage is the shortest relevant path along a solid insulating surface. TI’s isolation terminology separates those routes because air breakdown and surface tracking involve different conditions.
The same two conductors can have different air and surface paths. A visible straight-line gap therefore does not automatically describe creepage, and an apparently long surface route does not establish the shortest air path elsewhere in the assembly.
02 / Voltage meaning
Continuous working stress and transient stress differ.
A working voltage describes the relevant continuing electrical stress under its stated convention.
A working voltage describes the relevant continuing electrical stress under its stated convention. A transient or surge describes a different time and waveform condition. Peak and RMS labels also need their quantity definitions rather than an assumed conversion.
Air spacing and surface performance can respond to these stresses differently. TI’s glossary connects their purposes to air breakdown and tracking. A single nominal voltage label cannot establish every insulation requirement across both paths.
03 / Environment
Air and surface conditions influence different mechanisms.
Air density and the surrounding environment can influence the air-path question.
Air density and the surrounding environment can influence the air-path question. Moisture, contaminants and the insulating material’s surface characteristics influence surface behaviour. A clean geometric drawing and an actual environment therefore describe different parts of insulation coordination.
IEC 60664-1’s public scope treats clearance, creepage and solid-insulation criteria within a defined equipment framework, with stated environmental boundaries. Those conditions are not removed merely because a device has an enclosure or a coating.
04 / Solid barrier
Insulating material is a third boundary.
Electrical stress can also act through a solid barrier rather than along its outer surface or through air.
Electrical stress can also act through a solid barrier rather than along its outer surface or through air. Material thickness and properties describe that route, which should not be substituted for a creepage or clearance statement.
Likewise, a thermal insulation-class label concerns a different property from the complete electrical coordination problem. The winding-class guide explains why a temperature designation does not supply every assembled insulation characteristic.
05 / Assembly effect
A component’s distances do not describe all nearby routes.
A component package can have stated boundaries while the board, connector or assembled cabinet introduces other conductive parts and paths.
A component package can have stated boundaries while the board, connector or assembled cabinet introduces other conductive parts and paths. The complete combination needs its own applicable scope. A component isolation statement is not automatically a statement about the whole converter.
Reference geometry and material identity also matter when two arrangements are compared. A coating, opening or changed part can affect different paths in different ways. This explains the scope distinction without prescribing a modification or assuming that one alteration improves insulation.
06 / Product scope
A principle is not a spacing prescription or approval.
The IEC reference is a public scope description, not a claim of reading every normative table or certifying a product.
The IEC reference is a public scope description, not a claim of reading every normative table or certifying a product. The condensation guide explains one environmental mechanism that remains separate from geometry alone.
No MARSTON creepage distance, clearance, material group, working-voltage limit or insulation certification is specified. This page gives no cabinet inspection, spacing measurement, electrical test, coating application or hardware alteration procedure.
Continue the review with Wind Equipment Condensation: Surface Temperature & Dew Point.
Continue the review with IP vs IK: Ingress & Mechanical Impact Enclosure Ratings.
Continue the review with Common-Mode & Differential-Mode Electrical Noise.
Review partial discharge, local fields and evidence scope as a separate insulation topic; keep that evidence scope distinct from geometric spacing.
General background: Texas Instruments: Air clearance, surface creepage and isolation terminology · IEC 60664-1 public scope: Clearance, creepage and solid insulation coordination. These references explain industry concepts; they are separate from the applicable MARSTON product and project documents.
Key concepts and conditions.
Read each quantity with its reference, units and stated conditions. A general relation does not establish a model-specific value.
| Concept / quantity | Meaning / relation | Conditions / limits |
|---|---|---|
| Clearance | Shortest relevant path through air | Conductors and environmental boundary are defined. |
| Creepage | Shortest relevant path along a solid surface | Surface material and condition remain relevant. |
| Voltage stress | Working, transient, peak and RMS meanings | Different stresses are not interchangeable labels. |
| Solid insulation | Barrier through the material | Not a substitute for air or surface paths. |
| Assembly scope | Package, board, connector and cabinet boundaries | One component does not establish every path. |
Engineering questions.
Are creepage and clearance the same distance?
No. They follow surface and air paths respectively.
Does a long surface route prove sufficient air spacing?
No. The shortest relevant air path is a separate quantity.
Does nominal voltage define every insulation stress?
No. Working and transient stresses need their stated waveform and time meanings.
Does thermal class establish complete electrical isolation?
No. It concerns a different property and boundary.
Can a component statement approve a whole converter?
Not automatically. The assembled paths and applicable scope remain separate.
Are actual minimum distances or tests provided?
No. No product spacing or operating procedure is assigned.
Technical enquiry
Discuss the technical question.
Creepage follows an insulating surface; clearance follows a path through air. Share the model and applicable operating or design information for an engineering discussion.