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free operation of the studio.
However, the problem with this principle is that electric safety has the
highest priority. Since it is necessary to connect the protective conductor
to every device that has a power line connection, there are actually two
ground connections with almost every device, one thru the protective
ground and the other one thru the additional, high cross section, ground
cable.
Of course, this situation presents another risk for ground loops. At
this point we have to get back to the considerations about the mains
power installation to find a feasible solution since the modification of
all the equipment in a studio, in a way that makes it possible to use
the additional ground line as a protective conductor is impossible. In
addition to the problem that occurs with the necessary intrusion into the
devices, and the connected legal problems, like warranty, liability, etc., a
modification like this also affects the safety of each device. The problem of
finding an insurance company will underwrite this risk leads us to the point
that this principle cannot be used.
However, there is a way that is much easier and works properly. If the
mains power installation is executed in the way described above, we will
already have a low impedance ground connection to the central ground
node, which actually is the protective ground. We can leave everything
unchanged, if we use this main ground line as not only audio ground node,
but also as protective ground. Since the main ground conductor is part of
the mains power installation it is not a problem to accomplish this system
easily.
WE SHOULD MENTION THIS AGAIN…ONLY QUALIFIED PERSONNEL
SHOULD BE ALLOWED TO INSTALL AND/OR MODIFY HAZARDOUS
VOLTAGE, ELECTRICAL SYSTEMS.
THE ExAMPLES WE GIVE ARE VERY GENERAL AND ARE TO BE
TAKEN AS SUCH; IN ADDITION, SOME DETAILS MAY NOT APPLY IN
YOUR LOCAL AREA BECAUSE OF SPECIFIC LOCAL LAWS AND/OR
REGULATIONS.
WE ADVISES THAT YOU CONSULT A QUALIFIED ELECTRICIAN
REGARDING THE INSTALLATION OF ANY NEW ELECTRICAL
SUPPLY, OR THE MODIFICATION OF AN ExISTING SUPPLY. BY NO
MEANS, WILL WE BE LIABLE FOR ANYTHING THAT YOU DO.
Let’s put this together. We use the high cross section ground line from
the basement of the building not only as audio ground node but also as
protective ground. If we now install additional, high cross section ground
connections to the devices in the studio, we simply parallel the existing
protective ground that already exists. If commonly used power cords and
electric installation is used, we will have a cross section of the protective
ground of 1.5 mm
2
from the electric distribution box to the sockets and
0.75 mm
2
to 1.5 mm
2
from the sockets to the devices. This differs from
country to country, but it’s always in the range. This cross section is
sufficient for electric safety. Our additional high cross section cable add
another 4, 6 or even 10 mm
2
just in parallel to the protective ground,
which means, that the particular device is now connected to the ground
node very well and that the protective ground is almost shorted by this
additional ground line. However, if for any reason the additional ground is
removed or fails, the original protective ground is still installed. Therefore,
safety is not a problem. The only point of importance is that there may
be no connection between the neutral conductor and the audio ground
conductor, for the reasons already discussed in detail.
If, for any reason it is not possible to implement this system, there is
another way to get the same result. However, this way is complicated
and expensive. The entire mains power of the studio has to be separated
from the mains power by a huge isolating transformer. When the isolation
transformer is installed, the secondary circuit of the mains power is
galvanically isolated from ground. The mains power has no ground
reference anymore, which means, that we are free to apply any ground
with a sufficient cross section as protective ground.
BEFORE USING THIS PRINCIPLE, MAKE SURE THAT YOUR LOCAL
RULES ALLOW THIS PRINCIPLE. EVEN IF THIS WORKS, IT MIGHT
NOT BE ALLOWED AT YOUR LOCATION.
