Creepage Distance

NYOJ,

Contamination is addressed in creepgae distance (although the OP had it BACKWARDS in is original statement). "Creepage distance" is the term used for IEC standards, in North America where we use ANSI, the term is "leakage distance", at least when referring to MV and HV insulators and bushings.

IEC 60815 (and others, depending on the equipment involved, but they are all the same I think):

Table I: Contamination level in relation to a description of the pollution in some typical environments.
I = light
II = medium
III = heavy
IV = very heavy

I couldn't find a specific PD reference for 60815, but this is from another IEC standard, they are essentially the same.

• Pollution degree I. No pollution or only dry, nonconductive pollution occurs. The pollution has no influence.
• Pollution degree II. Normally only nonconductive pollution occurs. Occasionally a temporary conductivity caused by condensation must be expected (example: product used in switchgear in a normally clean dry environment).
• Pollution degree III. Conductive pollution occurs, or dry, nonconductive pollution occurs that becomes conductive due to expected condensation (example: products used in heavy industrial environments that are typically exposed to pollution such as dust).
• Pollution degree IV. Pollution generates persistent conductivity caused, for instance, by conductive dust or by rain or snow.

Table II: Minimum creepage distance for each pollution level :
Level I : 16 mm/kV of highest system voltage phase to phase
Level II : 20 mm/kV
Level III : 25 mm/kV
Level IV : 31 mm/kV

For us in North America, the standard is ANSI/IEEE C57.19.100

Contamination

Voltage: L-G
Light 28 mm/kV
Medium 35 mm/kV
Heavy 44 mm/kV
Extra Heavy 54 mm/kV

Voltage: L-L
Light 16 mm/kV
Medium 20 mm/kV
Heavy 25 mm/kV
Extra Heavy 31 mm/kV

Notice they are the same. Wonders never cease...