PCB busbar spacing requires separate checks of the shortest air path and the shortest path along an insulating surface, including manufacturing and assembly tolerances. Working voltage alone cannot specify a universal distance. This guide uses IEC 60664-1 and TI insulation-design material to organize the information a drawing review needs.
Identify both ends of each insulation barrier
Map the high-voltage poles, low-voltage control area, protective earth and accessible metal. The applicable equipment standard determines whether a particular barrier needs functional, basic or reinforced insulation. Include solder fillets, terminal projections, screw heads and conductive washers when finding the shortest path.
Keep the two distance calculations separate
Clearance measures an air path and depends on requirements including impulse withstand and altitude. Creepage follows an insulating surface and uses working voltage, pollution degree and material group. CTI helps establish the material group; it is not the equipment's insulation-voltage rating.
- Record RMS or DC working voltage separately from repetitive peaks and transients
- Specify pollution degree, material group and maximum operating altitude
- Evaluate minimum dimensions and worst-case assembled positions
Check altitude and slots in the actual geometry
IEC 60664-1 includes guidance for installations above 2,000 m. Apply the altitude requirements of the relevant standard to the clearance assessment. A PCB slot can change a surface path, but whether it counts depends on its geometry and the applicable rules. Nearby screws, overhanging metal and solder may still create a shorter air path. Review sections as well as plan views.
State what coatings and tests establish
Conformal coating, potting and insulating sheets require their own material, coverage, defect and qualification assessment. Do not reduce bare-board spacing solely because a coating will be added. A dielectric test addresses the specified test conditions; contamination, moisture and movement require the corresponding design and validation checks.
Attach an insulation-boundary sheet to the RFQ
Include the separated circuits, insulation function, standard edition, voltages, altitude, materials, pollution degree and required minimum paths. Supply an assembly section showing tolerances, burr direction and insulating parts. This gives the supplier a traceable basis for assessing a dimensional change.
Apply this guide to a project
Use product pages to identify the hardware family and the calculator for early estimates only. Acceptance depends on drawings, operating conditions and project tests.