Creepage and clearance calculator

How it works

Clearance is the shortest distance through air between two conductive parts, and creepage is the shortest distance along the surface of the insulation between them. This tool works out the minimum of each for a working voltage, a rated impulse voltage, a pollution degree, a material group, a type of insulation and an altitude, then checks the distances you have drawn. The rules follow IEC 60664-1; the figures in the tables come from a public manufacturer's guide and can be replaced with the figures in your own copy of the standard.

1. Find the rated impulse voltage. The impulse voltage the insulation must withstand follows from the supply's nominal voltage to earth and the overvoltage category of the place the equipment is connected (I for specially protected circuits, II for appliances, III for the distribution level, IV for the supply origin). You can also enter a value. It is rounded up to the next value in the preferred series of 0.33, 0.5, 0.8, 1.5, 2.5, 4, 6, 8 and 12 kV.rated impulse = table(nominal voltage to earth, overvoltage category), rounded up to the preferred series
2. Apply the type of insulation. Functional, basic and supplementary insulation use the rated impulse as found. Reinforced insulation uses the next step up in the preferred series for its clearance, and twice the basic creepage.reinforced: impulse used = next preferred step above the rated impulse; creepage = 2 x basic creepage
3. Look up the clearance. The minimum clearance at 2000 m comes from the impulse voltage used, the pollution degree and the field shape. Case A is a non-homogeneous field and is the usual choice; case B is a homogeneous field that has to be confirmed by test.clearance at 2000 m = table(impulse used, pollution degree, field case)
4. Correct for altitude. Thinner air withstands less voltage. Above 2000 m the clearance is multiplied by a factor that rises with altitude, interpolated between the table rows. Creepage is not corrected.required clearance = clearance at 2000 m x altitude factor
5. Look up the creepage. Creepage follows the RMS (or DC) working voltage, the pollution degree and the material group, which comes from the comparative tracking index: group I from 600, II from 400, IIIa from 175 and IIIb from 100. Printed wiring material has its own, smaller columns for pollution degrees 1 and 2. Between table rows the figure can be interpolated or taken from the next row up.creepage = table(working voltage, pollution degree, material group) x insulation multiplier
6. Take the governing distance. Creepage may not be smaller than the clearance, so the creepage required is the larger of the two. The governing distance is whichever is larger. The designed distances you enter are checked against both.creepage required = max(creepage from table, required clearance); pass if designed clearance >= required clearance and designed creepage >= creepage required

Sources

The methods and default figures rest on these public sources. The wording here is our own; read the source for its full text.

• IEC 60664-1:2020, Insulation coordination for equipment within low-voltage supply systems, Part 1: Principles, requirements and tests (opens in a new tab), International Electrotechnical Commission, 26 May 2020. The rules followed here: clearances (Clause 5.1), creepage distances (Clause 5.2), the impulse voltage by overvoltage category, pollution degree and material group. Cited by name; its tables are not reproduced.
• Application note: Low voltage control and protection products in high altitudes (document 1SAC200234W0001, Rev G) (opens in a new tab), ABB, April 2026. The public source of the built-in figures: its extracts of the clearance, creepage, impulse voltage and altitude factor tables, and a worked altitude example used in the tests. The link is a distributor's copy; search the document number if it moves.
• IEC 62368-1:2018, Audio/video, information and communication technology equipment, Part 1: Safety requirements (opens in a new tab), International Electrotechnical Commission, 4 October 2018. A product standard that applies the IEC 60664-1 rules to its own equipment and adds to them. Cited by name only.