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CHAPTER II
7.- EXISTING STANDARDS
7.3.- SUMMARY OF HIGH VOLTAGE REGULATIONS
The Technical Complementary instruction MIE-RAT-13 published in the
B.O.E. (Official State Gazette) 183 of 1
st
August 1984, section 1.1. sets the
maximum admissible step and touch voltages for EARTHING
INSTALLATIONS.
In sections 8.1 and 8.2 it establishes the requirement to verify that the
step and touch voltages are within the admissible limits. It establishes the
requirement for periodical checking every 3 years as a maximum. It lays down
that the measuring electrodes that simulate feet must have a surface area of
200 square cm each and that they each have a downward force onto the
ground of 250 N.
STEP VOLTAGE
-The voltage that can occur between the feet of somebody standing one
step away whilst the installation is operating" (I.E.C. standard 11-8, sec.176).
TOUCH VOLTAGE
-The voltage that a human body may experience whilst in contact with
housings and metallic structures that normally do not carry voltages.
MAXIMUM ADMISSIBLE VOLTAGES
- Maximum admissible step and touch voltages in a certain installation,
(B.O.E. 291 5-12-87), are determined by the following summarised formulae:
10 K K
Vp = -------------- Vc = -----------
t
n
t
n
Being:
K=72 and n=1 for times less than 0.9 s.
K=78.5 and n=0.18 for times between 0.9 and 3 s.
t = length of the fault in seconds.
For times between 3 and 5 seconds the touch voltage will not exceed 64
V and the step voltage 640 V.
For times above 5 seconds touch voltage will not exceed 50 V and step
voltage 500 V.
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