Page 230 - Electrical Safety of Low Voltage Systems

CHAPTER13

Safety Against

Static Electricity

and Residual

Voltages

If knowledge can create problems, it is not
through ignorance that we can solve them.
isaac asimov (1920–1992)

13.1 Introduction
Static charge can accumulate on different types of objects such as con-
ductive and insulated parts, high-resistivity liquids, and also gasses.
The static charge creates potential differences between the aforemen-
tioned elements, as well as between them and the earth, which may
1
reach 100 kV. As a consequence, an electric field possibly exceeding
the dielectric strength of the interposed matter among charged parts
(e.g., the air) is created and a spark accompanied by release of energy
(i.e., the heat associated with the spark) can occur. Static charge can,
therefore, be the source of ignition for flammable materials if they are
in the right concentration in air, and can even cause their explosion. 2
Flammable materials can explode due to their very rapid combustion,
which causes a sudden increase in their temperature and pressure. Ex-
plosive substances, instead, do not need to be in the right proportion
with the oxygen, and can explode even without it.

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