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For non-mains voltages, the IPC standard has a set of tables that define the clearance required for various<br />voltages. A simplified table is shown here. The clearance will vary depending on whether the tracks are on an<br />internal layers or the external surface. They also vary with the operational height of the board above sea level,<br />due to the thinning of the atmosphere at high altitudes. Conformal coating also improves these figures for a given<br />clearance, and this is often used on military spec PCBs.<br /><br />Clearances for Electrical Conductors<br />Voltage (DC or Peak AC) Internal External (<3050m) External (>3050m)<br />0-15V 0.05mm 0.1mm 0.1mm<br />16-30V 0.05mm 0.1mm 0.1mm<br />31-50V 0.1mm 0.6mm 0.6mm<br />51-100V 0.1mm 0.6mm 1.5mm<br />101-150V 0.2mm 0.6mm 3.2mm<br />151-170V 0.2mm 1.25mm 3.2mm<br />171-250V 0.2mm 1.25mm 6.4mm<br />251-300V 0.2mm 1.25mm 12.5mm<br />301-500V 0.25mm 2.5mm 12.5mm
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