design_for_dust

3. “Humidity and the Indoor Environment,” 
Minnesota Blue Flame Gas Association. 
www.blueflame.org/datasheets/humidity.html.

4. IEC 60947-1, Low-voltage switchgear and 
controlgear - Part 1: General rules, International 
Electrotechnical Commission, www.iec.ch.

FOR FURTHER READING

IEC 60664-1, Insulation coordination for 
equipment within low-voltage systems - 
Part 1: Principles, requirements and tests, 
International Electrotechnical Commission, 
www.iec.ch.

Lohbeck, David, “Safety isolation protects 
users and electronic instruments,” EDN, 
September 30, 2004. p. 59. www.edn.com/
article/CA454635.html.

Lohbeck, David, “Hazardous-voltage 
primer,” EDN, May 11, 2006. p. 39. www.
edn.com/article/CA6330100.html.

“Safety Articles and Videos,” National Instru-
ments Product Certification. zone.ni.com/
devzone/cda/tut/p/id/5427.

David Lohbeck is a principal safety en-
gineer with National Instruments. He is 
an ANSI Technical Expert and Assessor. 
Lohbeck has worked for Motorola, Dell, 
and TUV in international product safety, 
machine safety, and electromagnetic 
compliance (EMC). He has published nu-
merous articles on safety and EMC and 
is the author of CE Marking Handbook. 
dave.lohbeck@ni.com.

Table 2. Double or 
reinforced insulation 
for a 300-V product

Spacing type

Pollution degree

2

(typical 

products)

3

(industrial 

areas)

Clearance

3.0 mm

  3.0 mm

Creepage 
on PCBs

3.0 mm

10.0 mm

52   APRIL 2008

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