Hi John:
> In the CB Scheme "National Differences" document, Danish and Norwegian
> requirements (in 6.3.3.1 and 6.2.1.2, respectively) make reference to
> "equipotential bonding". Can anyone tell me exactly what equipotential bonding
> is? I assume that it is some form of grounding...would having a permanent
> connection to protective earth satisfy this requirement?
"Equipotential bonding" is the name given to the general
case, while "grounding" or "earthing" are the names given
to a specific case of equipotential bonding.
Equipotential bonding is a scheme of protection against
electric shock. All conductive parts in the local environment,
e.g., a room, are bonded together to create an equipotential
environment. If there is no potential difference in the
environment, then there is no possibility of electric shock.
(This is the principle behind bonding all conductive parts
within electrical equipment together.)
In practice, all conductive parts in the environment cannot
be bonded together. Instead, all conductive parts of
electrical equipment are connected to ground via the protective
conductor in the power cord. Likewise, all other conductive
parts in the room, e.g., plumbing, heating ducts, etc., are
connected to ground via some other means.
This is not a perfect equipotential environment, but it is
functional and practical.
The flaw is that during a fault to the equipment metal, there
is a voltage drop across the resistance of the protective
conductor that can allow the voltage on the equipment metal
to be as high as 1/2 the mains voltage (with respect to other
grounded parts) until the overcurrent device operates -- which
can be as long as 2 minutes. So, an electric shock condition
could exist for those 2 minutes.
If a true equipotential environment was established with
local (i.e., in the same room) bonding, then the voltage
drop across the protective conductor would not create a
potential difference between the equipment and the remainder
of the environment (because they are all bonded together
within the room). So, no electric shock condition would exist.
Best regards,
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 619 655 3329
Effective 6/12/99: +1 858 655 3329
16399 West Bernardo Drive FAX : +1 619 655 4979
Effective 6/12/99: +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
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