What Clearance and Creepage Are
Clearance and creepage are safety design distances used to prevent electric shock, arcing, and insulation breakdown in electrical equipment (including EV chargers).
– Clearance: the shortest distance through air between two conductive parts (or a conductive part and accessible metal).
– Creepage: the shortest distance along a surface (e.g., across a PCB or plastic housing) between two conductive parts.
Both are critical in power electronics, connectors, terminals, PCBs, and internal barriers.
Why They Matter
Clearance and creepage help ensure:
– No arcing or flashover at operating and surge voltages
– Safe insulation performance over product lifetime
– Robustness against pollution, humidity, condensation, and dust
– Compliance with electrical safety standards and certification requirements
– Reduced risk of nuisance faults and premature failures
In EV chargers, exposure to outdoor conditions makes creepage especially important because contamination and moisture can reduce effective insulation.
What Determines Required Distances
Required clearance and creepage are not “one-size-fits-all.” They depend on:
– Working voltage and transient/surge voltage level
– Overvoltage category (installation environment severity)
– Pollution degree (how much contamination/moisture is expected)
– Material group / CTI (Comparative Tracking Index of insulating materials)
– Insulation type: functional, basic, supplementary, reinforced
– Altitude (air breakdown voltage changes with elevation)
Clearance vs Creepage in Practice
– Clearance is most sensitive to air gaps and surge events (lightning/switching).
– Creepage is most sensitive to surface tracking, contamination, and moisture.
That’s why you often see designs using:
– Slots/cutouts in PCBs to increase creepage
– Ribs/barriers in plastic housings
– Potting or conformal coating (with careful validation)
– Better material selection (higher CTI)
– Controlled assembly tolerances to avoid distance reduction
Where It Shows Up in EV Chargers
Typical critical locations include:
– AC input terminals and relay/contactor areas
– Power supply primary/secondary separation
– Metering and measurement circuits
– DC bus and inverter sections (DC chargers)
– Connector and cable entry points
– Communication interfaces that must stay isolated from mains
Verification and Testing
Compliance is usually verified through:
– Design review and measurement (drawings + physical inspection)
– Material documentation (CTI ratings, insulation class)
– Dielectric withstand (hipot) testing
– Environmental testing (humidity, condensation, pollution simulations)
– Production quality controls to ensure consistent spacing
Common Pitfalls
– Assuming PCB spacing is enough without considering pollution degree and CTI
– Distance reduced by assembly: wires routed too close, screws, metal filings
– Conformal coating used as a shortcut without proper standard acceptance
– Water ingress or condensation creating tracking paths across surfaces
– Design changes that unintentionally reduce distances (new component footprint, connector swap)
Related Terms for Internal Linking
– Creepage and clearance
– Dielectric withstand test
– Insulation resistance test
– Double insulation
– Touch-safe design
– Earth leakage current