Equipotential bonding - commonly referred
to as bonding - is a very important measure in
reducing the risk of equipment damage and personal injury.
Bonding involves joining together all metalwork and
conductive items that are or may be earthed so that it is at
the same potential (voltage) everywhere. If
a component failure occurs, all circuits and conductors in a
bonded area will have the same electrical potential,
so that an occupant of the area cannot touch two objects
with significantly different potentials. Even if the
connection to a distant earth ground is lost, the occupant
will be protected from dangerous potential differences
resulting in injury or death from electric shock.
The earthng system is an important part of a lightning
protection system. The structure of buildings often includes
reinforcing bars, steel frames and deck slabs as the main
components. These components can also be used to form a low
impedance grounding system.
Earthing vs. Bonding
Earthing is intended to limit the
duration of voltages, while bonding is intended to
limit the magnitude of voltages. The danger of
electric shock due to indirect contact arises from the
following voltages which
may occur under earth fault conditions in an installation:
1. voltages between exposed conductive materials and
other exposed conductive materials
2. voltages between
peripheral conductive materials and other
3. voltages between
materials and peripheral conductive
4. voltages between exposed conductive
materials and Earth,
or peripheral conductive
materials and Earth.
purpose of earthing, where used for protective purposes
within a building or other facility, is to limit the
duration of the voltages in the above examples. This is achieved
by the operation of a protective device (such as a fuse or
circuit-breaker) under earth fault conditions, which removes
the voltages by causing an automatic disconnection of the
supply to the faulty circuit.
Without an adequate
earthing system in place, the protective device could not
operate as required under earth fault conditions. In
contrast, the purpose of bonding is to limit the magnitude
of the voltages in examples 1, 2 and 3 above. This is achieved by
electrically connecting (bonding) those conductive parts.