Electrostatics / Static Electricity
Static electricity as a natural phenomenon is generally known by the layman from discharge flashes on door handles after having walked over a carpet. These electrical discharges are generally no danger to people. There is, however, a great number of consequences of static electricity, some of which must be prevented at all costs.
These range from the destruction of electronic components to the explosion of entire factories.
A) Brief description
I. Creation of static electricity = Electric charge
B) Method of testing for electrostatic properties
Static electricity is always created when there is motion of fixed insulators or liquid substances, or to be exact, when they are separated. An extreme example is dusty air grazing a wall.
The voltage of a charge depends on the humidity. The drier the air, the higher the charges. Electronic components are extremely sensitive to this. Discharges as low as just 30V can destroy them and trigger faulty operations.
This creates great risks and thus incalculable costs. The fact that electronic components are nearly always shielded mitigates this problem.
II. Static electricity and conductivity
By selecting favorable materials, one can reduce, but never prevent, the creation of static electricity. What can be done, is to prevent excessive charges from building up on people and objects by ensuring that the charges created do not accumulate, but are immediately and evenly conducted away. If static electricity can be continuously conducted away via a grounding connection as soon as it is created, the charge cannot become large enough for a discharge flash (electric shock) to develop.
III. Static and dynamic electricity
Dynamic electricity is the electric current generated continuously by power stations, which flows into cables and contacts as voltage. Static electricity, on the other hand, is not fed by a voltage source, but rather, is a one event, which after its discharge is not immediately available again.
I. Resistance measurements; quantity measured: Ω (Ohm)
Due to the different test conditions, the contact resistance of a location can only be approximately calculated from the contact resistance (R1 - Process A - DIN EN 1081). From experience, however, it is known that conductive floors with R1 < 106 Ω do not meet the VDE-requirements. With all types of coverings, moisture in flooring systems can also cause lowering in the contact resistance of a location.
Most tests are carried out in a prescribed test atmosphere, which is not uniform for the various standards.
a) Contact resistance
II. Charging measurements; quantity measured: kV (kilovolts)
(R1 - Procedure A - DIN EN 1081)
The electric resistance, measured on a sample between the tripod-type electrode on the surface of the floor covering and an electrode on the bottom side directly on the other side.
b) Ground resistance
(R2 - Procedure B - DIN EN 1081)
The electric resistance, measured on an installed floor covering between the tripod-type electrode pressed on the top side and earth.
c) Surface resistance
(R3 - Procedure C - DIN EN 1081)
The electric resistance, measured on an installed floor covering between two tripod-type electrodes set up at a distance of 100 mm (3.94") from one another.
d) Contact location resistance
(RST DIN 57 100 / VDE 0100 T-10)
What is measured in this case is the resistance between the surface of the installed floor covering to the ground potential.
a) Walk test (DIN 54 345, T2)
This measures the voltage charge of a test person who walks on the installed floor covering with shuffling feet.
b) Instrumental testing (DIN 54 345, T3)
Here the walk test cited above is simulated with a piece of equipment. This test can only be carried out in a laboratory.
Elastic floor coverings are also antistatic if they are conductive according to Section c) 2.
Floor coverings are antistatic if, in general, they do not allow annoying electrostatic charges to develop. This is true if, when subjected to the walk-on test, the charging is 2.0 kV
Floor coverings, whose resistance to earth of R2- Procedure B is 109 Ω, are conductive. Even lower resistance levels are frequently required, however.
As defined by DIN 5700 / VDE 0100T410, Section 6.3.3, floors insulate (provide security against contact voltage from mains current), if the contact resistance of the location RST does not fall short of the following value: 50 kΩ = 5 x 104 W for installations with rated voltages below 500 V. 100 kΩ = 1 x 105 Ω for installations with higher rated voltages.