Key principles.
σ in S/m
Reciprocal of resistivity. Copper 5.96×10⁷ S/m.
ρ in Ω·m
Material resistance. Silver 1.6×10⁻⁸ Ω·m.
εr
Capacitance increase factor. Air 1, water 80.
kV/mm
Insulation failure voltage. Air 3 kV/mm, glass 30+ kV/mm.
µr
Magnetic susceptibility. Iron 5000, aluminum 1, copper 1.
Tracking resistance
Comparative Tracking Index. Higher = better.
FAQ
Reciprocals. σ = 1/ρ. Both express same property.
Generally decreases with temperature. Specify per service condition.
Magnetic field design. Iron strongly affects. Aluminum/copper minimal.
Per relevant property: conductor (low ρ), insulator (high breakdown), magnetic (high µ).
ASTM D257 resistivity, ASTM D149 dielectric strength, ASTM E1300 permeability.
Manufacturer datasheets standard. ASM Handbook comprehensive. NIST for primary research.
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