design_for_dust

One thing you need to do is use the 

proper insulating materials and then pro-
vide sufficient distance between compo-
nents and PCB traces. Electrical insula-
tion, a dielectr ic, resists the flow of 
electric current. Dielectric strength is a 
measure of an insulating material’s ability 
to withstand voltage stress without fail-
ure. The amount of insulation you need 

depends on the voltage and intended en-
vironment of your product.

Plastics and air are two common insu-

lators used to separate circuits and pre-
vent unsafe current flow. Using air as in-
sulation raises concerns about 
environmental pollution. The 
addition of solids, liquids, or 
ionized gases and moisture 
can reduce dielectric strength. 
Product standards such as IEC 
60947-1 classify environmen-
tal conditions according to 
the amount and frequency of 
occurrence of hygroscopic 
dust, ionized gas, and salt, 
with regard to relative hu-
midity (Ref. 4). 

Product standards also 

specify “pollution  degrees” 

for various types of products. The pollu-
tion degree defines the level of dust and 
water pollution within a product’s oper-
ating environment. Pollution degrees 
range from 1 to 4, with higher numbers 
indicating more dust and water in the 
environment. Table 1 explains the four 
pollution degrees.

Pollution degree 2 generally applies to 

homes, offices, and laboratories (Figure 
2

). For example, pollution degree 2 is ap-

propriate for information technology 
equipment (IEC 60950-1), test and mea-
surement equipment (IEC 61010-1), 
household appliances (IEC 60335-1), 
audio-visual equipment (IEC 60065), 
electronic equipment (ECMA-287), and 
industrial control products (UL 508).

Insulation, creepage, and 
clearanceAn environment’s pollution degree, com-
bined with electrical and environmental 
factors such as working voltage and over-
voltage category, can affect a product’s in-
sulation. The working voltage is the high-