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11.08.2011
IG-178-GB
version 01
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GENERAL INSTRUCTIONS FOR
CMS-17
SWITCHING AND BREAKING SUBSTATION
3.5.2. External Earthing Circuit
The installation project must include a section corresponding to the earthing installation
(check the Utility’s standard project), as well as the justification of its size. The requirements
for this type of installation are established in the regulations governing Earth Connection
Installations.
Below is a recommended method for the installation of the earthing network from the
operator safety perspective:
Create an equipotential surface for both the switchgear and the operation area.
Each project should include the study of the most suitable earthing diagram.
The copper braid cross-section, the terminations' contact surface and the tightening
torques must be suitable for a fault current delimited by network protections. It is
recommended an external protective earthing network of bare copper wire with a
minimum cross-section of 50 mm
2
.
It is recommended that the external earthing circuit is installed simultaneously. To this
end, it is recommended to check the Switching and Breaking Substation installation
standard project available at the Electric Utility that provides the service and is
responsible for maintaining safety in the worksite earthing installation.
Adequate earthing measures around the Transformer Substation must be provided to
prevent dangerous touch and step voltages.
The recommended tightening torque for electrical connections in the earthing network
is shown in the following table:
Metric
Tightening Torque [Nm]
8.8 Steel
A2 Stainless
M8
21
M10
38
M12
60
