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For the realization, the main ground node, which in this case can be the
central ground point of the building, or a separate earthing electrode, or
a combination of both, has to be connected to the protective conductor
at the studio installation that is driven by the secondary winding of
the isolation transformer. As mentioned above,
you must obey your
local rules as far as the installation of isolation transformers
are concerned
.
These rules are different from country to country.
In some countries, it is only allowed to install one single device to an
isolation transformer but not to install a system like this.
Gather all
necessary information and make sure that an installation like this
is in accordance with the local safety regulations.
Even if such
system works properly, it is under your responsibility to obey
the local rules and you will be liable for any damage and harm
that is caused by this installation. By no means, we will be liable
for anything that you do.
We only describe possible ways of an audio
installation, but we cannot tell if everything that is listed here is allowed at
your location.
If your studio is installed in a room with an existing, old electrical
installation, it is necessary to check this installation. Figure out, how the
protective ground is wired and if it is connected to another electric circuit.
Check if the cross section of the protective ground is appropriate and
check how the different circuits and wall outlets are distributed among the
fuses. If there is any connection of the protective ground to another room
or sub-distribution you might have serious problems. It is necessary to
make sure, that the protective ground of the audio mains power is clean
unless you risk many dubious problems. If might be necessary to replace
cables, or add new protective conductors with sufficient cross section,
replace wall outlets and rearrange the distribution and add new fuses. You
need to have a skilled, professional electrician for this task, who is familiar
with the special problems of audio installation and grounding.
2.2 Common grounding problems
Even if the principle of the ground installation is perfect, some
common situations should be considered.
Video
This is the basic problem of any TV studio. Since all video connections are
unbalanced, it is a hard job to maintain a clean audio ground situation
with all the video equipment. You will need many audio transformers to
make sure that your ground system is not polluted by the video signal.
In many real-world situations, only pragmatism works, since you will not
be able to make sure that an appropriate ground system can be installed.
If this is the case, use the highest possible cross-section for any ground
cable that is possible. If you cannot control the current in the different
ground lines, the only possible way is to make the entire ground system as
strong (as low a resistance) as possible.
Antennas
If a receiver or any other device is part of the system that requires a
roof antenna, you can be sure that the antenna will inject a different
ground potential into the system. An antenna must be grounded just for
lightning protection and you can normally not control the ground potential
of this antenna. Make sure that this will not affect your studio ground. If
necessary, install audio transformers and isolate the entire device from the
rest of the studio.
Computer network connections
Like video, the commonly used computer network connections of the RJ45
and 10-BaseT types are grounded on both sides of the line. A computer
network installation is always a ground disaster, since all the computer
devices, workstations, monitors, printers, network hubs, switches and
repeaters may or may not be connected to a protective conductor,
depending on the power supply of the particular device. In any case, all
components are ground connected with the network cables, which have
high impedance. Since it is not important for the function of the networks,
no one takes care about the implementation of this ground connections at
all. This is another way to spoil a good audio ground system.
Telephone lines and modems.
Any kind of telephone line or modem can create the same problem. In
most cases, only audio transformers can be used to keep the ground
system clean.
