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Re: Noisey Earthground????

Posted by Jacques (A) on August 29, 2005 at 04:26:27

In Reply to: Noisey Earthground???? posted by Dan Banquer on August 28, 2005 at 12:50:08:

>Interesting stuff Jacques; I'm just not seeing or hearing any evidence of some of the issues you are pointing out.
>I live about 50 yards from a Ham Radio Operator with a 100 watt transmitter and a moveable directional antenna
>and have no issues at the present time.
Which issues?
As for RF "spraying" into an enclosure through long slots and
large low capacitance stand-offs, it is noticeable above 800MHz/ 1.0 GHz
for standard size enclosures.
As for ground transmitted RF perturbation, we' ll talk about it below.
As for mains common mode RF perturbations, they are well filtered by your
EMI/RFI filter at the AC input. Short leads and good cabling practices will
avoid to spread RF leak in ghe enclosure through mainly induction and even
raciation at UHF and above. I bet you use these practices.
As for mains differential RF conducted perturbation, above 20MHz, most are
cut off by the common mode filter and the X capacitor which follows. Below,
it's filtered out by the diode dampers, if you use them, or by the tank
capos and their parralel MKT. Even by the series regulator.

As for the Ham Radio, which frequency? Decameter band and anything below
some tens of megahetz is unlikely to cause you trouble.
And also, I do think your equipment is well built, since, according to
reviewers, it doesn't need should-be unacceptable workarounds to sing fine
(I mean by workarounds: long heating periods, super-quiet mains, exotic
interconnects, -worse- exotic power cords or any quantic wannabe)

The issues I addressed in my previous post are those I found relevant each time I
had to conduct EMI/RFI certification on the airborne equipment I built with
my team for the company I was working at the time (10 years ago...).
The best example of these equipments was in a manner audio-related: it was a
maintenance prediction computer for heavy helicopters NH90. We used about 20
mikes and accelerometers (or even more if needed) set around the gearbox of the
rotor, then analyse the sound coming from these sensors, correlate it with
the rotor speed and deduced gear pieces speed, and determine if any torque
unbalance arises (a gear losing a chip pf metal for example) Combined with
a metal detector in the filter of the gear oil pump, it gives a very
predictive system, currently certified even for civilian uses (oil platform
staff rotating). The bandwdith of the input was 17Hz to 35KHz (17Hz is the
rotation speed of the rotor's blades). Length of interconnect was in the
10m range. Dynamic range was in the 90dB plus: the DSP had to substract the
main 17Hz peak and its predicted harmonics, and also all the gears mains
and predicted harmonics (many are in a fractional ratio with the blade's),
analyse the remaining, detect its enveloppe, threshold it and send reports
and alarms as needed. Power supply is two redundant 28V DC (that is 17 to
36volts with brownouts, high EMI conduted perturbs etc etc).
This equipment (a single box 30*20*20cm) is installed in a rack. Just below
is the weather radar: 100ns pulses of ...20MW peak power at a repetition
rate about 1KHz. Just above is the magnetic compass with its exquisite
sensitivity in the tens of microtesla. All this stuff having to work
together. And it vibrates severely. No magic dampers here. Obviously, no
way to heavily shield the box: the less weight possible is paramount. So,
the inputs were filtered without annoying audio, same with the PS.
Ah, I forget: should work unnoticed after a max 2
seconds peiod of knock-out in case it gets a direct lightning stroke of
20KA on 5/20/50µs wave.
All that gave me an experience. And it was EMI/RFI certified on the first
official EMI/RFI testing (the software took much much longer time, but
that's another story... And I was not the software guru)

>As far as cabling is concerned I use a microphone cable with a twisted pair
> and a braided shield. About all the rest of the equipment comes with a RFI/EMI Filter
> at the AC input, the stuff that doesn't gets plugged into Tripplite Isobar.
I do the same. I use Van Damme starquad cables, similar to Belden 1192A. I
bought 4 *100m rolls (4 colors), so I'll stay stick on it, and it's really
good and if not cheap, at least not expensive ($1.5/m or even less).
As for mains filter, I use Schaffner's, since until now I calculated it was
not interesting to build them from scratch. It is going to change

>Now one thing you can tell me; Where is this noisey earth ground plane you
> are referring to? because I can't seem to locate that here.
Well, as we say in french it's un abus de language (abuse of language).
Obviously a single reference cannot be "noisy" by itself. I was referring
to a system in which different interconnected equipments have their
respective earth connection done in different points, with a perturbation
voltage between them. For example, you connect the preamp and the sources
together in a rack near the listener to a nearby wall plug, and the PAs
between the speakers connected to another wall plug. If you have somewhere
on the way of one of these earth wires an equipment which feeds conducted
RF into the earth wire (marginnally compliant SMPS or even big motor for
HVAC), it will build up a voltage difference between the 2 earth plugs used
by the system.
It's very common and is the source of many problems in instrumentation,
factory automation, avionics etc. As long as you share the same mains
connection (and therefore the same earth if compliant to the code) in
a star fashion, you're immune to its effects (if you like calculations, I
can send you a short problem I ask every other year to the EE students in
their final test. I have to translate it in english. Fun)

>P.S. Here in the states the earth ground for most of us goes right to the
> incoming water pipe, no plastic or PVC is allowed for incoming water pipes
> or in the street for incoming water. What is the construction code in France for this?
Nothing special for France, all standards here are on a european basis.
Anyway, it's very very different.
Metal water pipes in the house (only copper and stainless steel are
allowed, but the later does not solder easily, so it is used only by labs
and hospitals) are grounded at the point of use (each sink shall be
grounded), but the ground is forbidden to go throughwater pipes. Most incoming
water pipes are plastic, so... (better: only plastic incoming pipes are
allowed nowadays, only old building use metal incoming pipes, mostly
...lead, so, with lead phasing out, it's likely to change soon)
It is mandatory to have a special copper or stainless steel rod (about 1m
long, to which the main entrance box is connected via heavy gauge copper
wire with a maximum of 2 90° turns. Earth resistance at the rods is to be checked
for receipt of a new house, or when selling it (depends on the state regulations).
A max of 25 ohms is allowed. If greater, a second rod shall be used with
conditions.
The rationale in non using the water pipes is (1) to avoid losing workers' life
in case of a direct lightning stroke onto a house without a earthing rod.
If the soil is very resistive (rock or dry sand), the stroke can run on
long distances and kill remote workers.
(2) Also, problem of liability: you installed lightning protection
in your main box, got a direct lightning stroke but got all your cherished
audiophile equipment cooked black smoky.
Who's liable for the insurance? You (you should unplug your valuable assets in
case of a storm), the protector manufacturer, the water company who bared
the pipes in the street for fixing a leak _this_morning, the cherished
equiment manufacturer (you ;-), God? Not easy to unscrumble
(3) Most metal water pipes are set at a DC voltage of several volts, thanks
to low voltage /very high current power supplies. The aim is to counteract
corrosion by putting the pipe as an anode, the cathode being a disposable
grounded block of zinc or magnesium at the water sation (near the power
supplies). This way, you set an electrochemical potential that prevents
oxydation of the pipes (that is loss of electrons to become positive ions)
In EU, we considered it is better to let this system work alone, apart from
customer power distribution.

Another difference in these matters is that in EU (maybe not in whole UK??)
distribution is done this way: 20KV triphase goes to the Delta primary of a
triphase transformer (no monophase xformer like in america, not only the
US), its secondary is Y, and the center of the Y is the neutral. At the
transformer premises (would it be a cabin, a room or just a pole), the
center of the Y is connected to the earth through a metal rod. Then the
distribution company makes its phase balance between customers, most of
residential customerjust use a 230V monophase. Only 3 phases and a neutral
are distributed for 230V
At the customer mains box, there is NO connection between the neutral and
his/her earth (rod as explained above). Both mains, hot and neutral, stay
floating as seen by any equipment connected to them. Very diffrent from the
american way.
advantages and drawbacks of the european vs american solution :
EU: as the mains shall be floating, it's easy to check out: just
disconnect the mains breaker, and check with an ohmmeter you got kiloohms
between any AC wire and earth.
US: neutral and earth are connected at the customer's. According to the
code, it shall be connected at a single point. To check this out, you need
several disconnections. If connected to several points,
it can generate noise, and it does often, according to what I read on
several forums. See the link below that I wrote on how to solve such
problems. Not really easy.
EU: since the mains are referenced to the earth only at the transformer's,
any voltage build between the earth at the xformer and the earth at the
customers' will be seen as a common mode voltage "lifting" both AC mains "above" the earth (make the following calculation: a stroke hits behind the
xformer. Let have the 2 rods resistance=25ohms, the ground resistance
between the rods is 40 ohms, the strike-to-transformer-rod resistance
is 20 ohms, the strike peak is 20,000A (small). What voltage will build up
between the mains and the earth at the customer's?)
You see it's easy to obtain kilovolts. A workaround is to use a primary
lightning arrester at the intrance main box, which diverts the stroke .
Also, we use special arresters between earths of different buildings
(different rods), if systems are spread in those several buildings.
US: since neutral is connected to earth also at the customer's premises,
there is no build up of dangerous common mode voltages (but you can get the
hot wire really very very "hot" in case of a stroke on the wire).
So, use of arresters can be laxer than in EU.
Historically, this difference in way of connecting earth has two roots: the
much greater distances between houses in rural america than in Europe
and the much higher thunderstorm incidence in the US (Fl, middlewest) than
in the mild europe (reference Lighning and Lighting protection, by WC Hart
and EW Malone, ed. Don White Consultants Inc,ISBN0932263-14-3)

As for audio use, the situation is simpler in EU, as we may consider the AC
mains as floating. So, you can easily build your own reference in equiment
by 2 Y caps. But the main advantage is that you are free from the bad
neutral/earth wiring syndrome that hits so many american audiophiles (link again). On
the dark side, you are required (well, depends on regulations at the states
level, but you have better, anyway) to install _properly_ (no angles,
direct connection to the rod etc) a primary lightning arrester.
Nothing perfect for us flesh creatures ;-)

• Hum and Buzz and neutral/earth wiring problems   (Open in New Window)

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