Calculator Inputs
Formula Used
Peak voltage: AC RMS voltage × √2. DC voltage stays unchanged.
Clearance: max(peak voltage ÷ air strength, impulse voltage ÷ air strength) × pollution factor × altitude factor × barrier factor × board factor × safety factor.
Creepage: max(0.40, working voltage ÷ 160) × pollution factor × material factor × coating factor × barrier factor × board factor × safety factor.
Final isolation gap: greater value between clearance and creepage.
Available gap margin: available board gap − recommended isolation gap.
How to Use This Calculator
Enter the working voltage between isolated conductors. Select AC RMS or DC. Add the expected impulse voltage if surge exposure is possible.
Choose pollution degree, material group, surface coating, barrier type, and board condition. Enter altitude because air insulation changes above normal elevations.
Use the default air withstand value for early screening. Adjust it only when your engineering rule gives a better value.
Press calculate. Review clearance, creepage, final recommended gap, and margin. Download CSV or PDF for project records.
Example Data Table
| Example | Working Voltage | Impulse Voltage | Pollution Degree | Material Group | Coating | Estimated Use |
|---|---|---|---|---|---|---|
| Logic isolation | 48 V DC | 500 V | 2 | II | None | Digital isolator board |
| Mains supply | 230 V AC | 2500 V | 2 | IIIa | None | Primary to secondary barrier |
| High voltage sensing | 600 V DC | 4000 V | 3 | II | Basic | Measurement divider area |
Article: Circuit Isolation Gap Planning
Understanding Circuit Isolation Gap Design
Isolation gaps protect people and electronics when circuits carry different potentials. The gap creates a physical barrier between conductive parts. It limits flashover through air. It also reduces tracking along the board surface. A good design checks both clearance and creepage. Clearance is the shortest air path. Creepage is the shortest surface path. Each path responds to different hazards, so both values matter.
What This Calculator Reviews
This calculator estimates practical spacing for early printed circuit board planning. It accepts working voltage, impulse voltage, pollution degree, material group, altitude, coating, and safety factor. The tool converts voltage stress into an air gap estimate. It then applies correction factors for environment and height. It also creates a creepage estimate from voltage and material behavior. The result is a planning value, not a final certification limit.
Why Factors Change the Gap
Higher voltage needs more insulation distance. Dust, condensation, and conductive residue can lower surface resistance. Greater altitude lowers air density and reduces withstand strength. Lower CTI materials can track more easily under stress. Conformal coating may improve surface protection, but only when specified and applied correctly. The safety factor adds extra margin for tolerances, aging, contamination, and assembly variation.
Using Results Safely
Use the calculated gap as a conservative screening number. Compare it with the exact rule used by your product standard. Medical, mains, battery, industrial, and communication equipment may follow different tables. Production designs should include slot geometry, solder mask limits, connector spacing, humidity, expected surges, and manufacturing capability. Keep primary and secondary circuits separated. Avoid copper points that concentrate electric fields. Leave inspection space near terminals. Document every assumption before layout release.
Layout Review Tips
Good isolation planning begins before component placement. Place the isolation barrier as a visible layout feature. Route signals across it only through rated parts. Keep test points, mounting holes, shields, and heat sinks away from the gap. Review both normal operating voltage and expected surges. This habit prevents late redesigns and improves production inspection quality. Teams can review assumptions faster. Engineers can revise spacing before prototypes ship.
Design Notes
The calculator is useful when selecting optocoupler spacing, relay pads, transformer bobbin routes, isolated supply barriers, and high voltage sensing circuits. It helps compare options before drawing copper. Final approval must come from applicable safety standards, test labs, and qualified engineering review.
FAQs
What is an isolation gap?
An isolation gap is the spacing between conductive circuit parts. It helps prevent arcs, tracking, leakage, and unsafe contact between different voltage areas.
What is the difference between clearance and creepage?
Clearance is the shortest air path. Creepage is the shortest surface path across insulation. Circuit boards need both checks for safer spacing.
Can this replace a safety standard?
No. This calculator is for planning and early review. Final designs should be checked against the exact standard required for the product.
Why does altitude matter?
Air becomes less dense at higher altitude. Lower air density can reduce dielectric strength, so clearance may need extra margin.
Does conformal coating reduce the required gap?
Coating can help surface insulation when specified correctly. It should not be used blindly. Confirm coating rules, thickness, coverage, and inspection requirements.
Which material group should I choose?
Use the group that matches the board material CTI rating. If unknown, use a more conservative group until the laminate data sheet is checked.
What is pollution degree?
Pollution degree describes contamination around the insulation. Clean sealed circuits need less allowance. Dust, humidity, or conductive residue increases spacing needs.
Why does the final result use the larger value?
Clearance and creepage protect against different failure paths. The larger value gives the safer planning gap for circuit layout review.