Page 127 - Electrical Safety of Low Voltage Systems

110 Chapter Six

system from TT turns into IT, without having the safety requirements
characteristic of this system (see Chap. 9).

6.10 Main Equipotential Bonding
As anticipated in Chap. 4, the equipotentialization between ECPs and
EXCPs, which can be simultaneously touched, reduces to safe values,
oreliminates,potentialdifferencesarisenbetweenthem,inearthfaults
conditions.
Equipotentialization is practically achieved by connecting all the
EXCPs to the grounding system. In particular, the following items
must be linked together at the main grounding bus of the building to
realize the main equipotential bonding (MEB) (Fig. 6.17):

Pipes supplying services within the building (e.g., gas, cold

water, etc.)
Central heating and air-conditioning systems (if present)

Structural metallic parts of building

Reinforcing bars embedded in concrete

Circuit protective conductors

Main grounding conductor

The EXCPs originating outside of the building must be bonded as
close as is practical to their point of entry within the building.
The remarkable “by-product” of the main equipotentialization is
the reduction of the resistance of the house grounding system be-
cause the EXCPs act as electrodes in parallel to the made-electrode(s)

FIGURE 6.17 Main equipotential bonding.