Each panel has its own star grounding setup, then panels are bonded
between each other with a heavy cable.
That's pretty much standard these days.
I'm not making this stuff up. That's how its done.
When we are talking about "modules", I am talking about industrial steel
control panels. Some are 7 feet tall, 2 feet deep and 4 feet wide.
Some of them are big enough that you can stand inside of them with the
equipment installed in the panels. Some are more like control closets
than panels. Sometimes they are bolted together as below, sometimes
they are free standing and spread around a machine. Sometimes they are
much smaller. But if they have large drives, the panels pretty much
have to be large just to accommodate the large power cables and heat
loads. Some are air conditioned and some are not.
Similar to this:
http://www.elettronicalucense.com/portfolio/industrial-automation/
If you use decent equipment and follow their shielding recommendations,
noise is typically not an issue. But each device has undergone CE EMI
noise testing as well.
Dave
On 7/13/2018 1:48 AM, Erik Christiansen wrote:
On 12.07.18 15:33, John Dammeyer wrote:
So what happens when the equipment with the 24V supply is 30m long in
multiple steel frames? There would be a bonding wire from frame to
frame since you wouldn't want to bond one end to one AC ground outlet
and the other end to a different AC ground outlet.
Rather than chain a whole lot of modules on one long ground wire, where
each can interfere with the others by imposing HF noise on the common
ground impedance, thereby coupling it into the others, I'd wire them
individually back to the power supply. ("Star Earth", as Gene so rightly
points out.)
If there is internal DC connection to the equipment case, I'd provide
isolated mounts to defeat the earth loops which would most likely
otherwise cause problems.
If there's RF EMI into the equipment from a hostile environment, then
I'd be tempted to connect the metallic case to its internal equipment's
earth via a good RF bypass capacitor, to put the circuitry's Faraday
cage at earth potential.
...
What about if you have a vehicle instead. Might have equipment
mounted on frames that need to be bonded together. If they run an
independent battery pack and/or genset then the DC ground doesn't need
to touch the frame. But what if the vehicle 12V battery which does
have negative connected to the frame also provides some sort of
vehicle connection. Say a radio that has a modem that connects to a
PC.
One connection, as at the battery would be fine. It's earth loops which
best radiate EMI, proportional to the area of the loop antenna.
Logic would dictate you want the DC ground of everything connected to
the frame with some bond wires even if just for lightning protection.
But now you run risk of ground loops on the 12V circuits interfering
with the system battery pack.
I'd put gaseous arrestors on external lines as primary protection,
followed by MOVs or transorbs further inboard, with some impedance
between, to further clamp the surge not entirely swallowed by the
arrestors. But I'd try to read up on that bit first. Grounded shielding
on external wiring has to help too.
Erik
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