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Wierd Ground Problem?

Last week we moved a video recording computer (PVR) from it's
downstairs location (where it was working fine) to an upstairs
location, beside our TV. At the same time we changed the computer case
(to a new, sleek black one), used a different power supply and tacked
on a wireless USB keyboard and mouse.

After doing that we started hearing a low frequency hum on the PVR
audio. Yesterday, we also noticed a similar hum on another PVR's
audio. That PVR is still in the basement - directly below the upstairs
PVR.

We went through a ton of diagnostics trying to isolate the hum.

We found the audio coming out of the satellite dish was clean. We
tested this by plugging headphones into the RCA out jacks on the
satellite receiver.

The PVR 'Windows' session sounds (startup, etc.) did not hum - it was
only when we started the video program (BeyondTV using a Hauppauge 150
PVR card) that we got hum.

So we surmised the hum happened once the signal got into the PVR (we
could hear it using headphones plugged into the audio-out jack on the
PVR when we played video).

We checked everything, dismantling the PVR, trying to supply power to
it from a different house circuit, etc. We thought it might be the new
computer power supply - so we took out the old one and tried it - same
problem. At one point we realize the hum will appear when we plug in a
computer power supply to A/C and just touch the power supply box edge
to the PVR case. The computer power supply does not have to be turned
on -or - any of it's output connectors plugged into anything in the
computer - just as long as it has the 3 prong power cord stuck into
it's backside. That test was done with the power supply cord being
connected to a 120 V outlet in the kitchen.

We then begin disconnecting cables to EVERYTHING in the livingroom
(wireless phone, etc.) - and finally the hum goes away when I start to
unscrew the satellite dish RJ6 cable connector from the satellite
receiver (the RJ6 cable from the dish to the receiver).

The satellite receiver was connected to the PVR through an S-Video and
2 RCA connectors but those cables had already been removed in our
disconnecting process. The satellite receiver was plugged into a UPS.
We had turned off the UPS and unplugged it from the wall during our
cable disconnecting process.

I re-tighten the RJ6 connector and the hum is still gone. (I was kind
of hoping it would return so I could recreate the problem & verify that
this was the source of the hum).

So we suspect some sort of 'bad or looping ground' situation related to
the satellite cable.

The satellite cable and dish are grounded on the outside to a 4 foot
copper grounding rod - but they are not grounded directly to household
ground. We theorized (because we are not electrical specialists we can
only theorize) that grounding with the 4' rod was sufficient given that
the dish is low on the roofline and that the satellite cable would be
further grounded once it was screwed into the satellite receiver case
seeing as the case would be grounded to the household ground through
the a/c outlet as the receiver has a 3 prong grounded plug. We do not
have an easy way to run a direct ground to household ground - without
snaking a ground wire around 3 sides of our home (as all basement
ceilings are drywalled).

I recall seeing an article talking about the need to ground these
dishes to household ground & wonder if this is a real life reason to do
that.

Any idea how this would happen & what we should do to fix it?

Thanks, Cindy
 
C

Charles Schuler

Jan 1, 1970
0
Hi Cindy:

I really cannot follow your post as to the specific details of what was
hooked to what. I'll offer some general 60Hz hum rules:

1/ Grounds are not all the same. When two grounds are connected together, a
current can result (and often does). This current can induce a hum signal
into low-level signal conductors.

2/ It is sometimes necessary to open one end of the shield connection on
signal cables to eliminate the current flow caused by ground voltage
differences.

3/ Magnetic fields are often the culprit. Low-level signal cables located
near motors and transformers can pick up a significant hum voltage.

The above are the "biggies". There are others.
 
Are you using a 'single point ground' for all the equipment, or a
multi-point grounding arrangement?

If you are using a multi-point ground for the different pieces of
equipment, you could very well be seing the results of a "ground loop"
causing a.c. current to flow between the the shields/commons of the
cables connecting your various units and an a.c. offset voltage
appearing in series with each of the signal lines.

Given the symptoms that you've posted, I'm inclined to believe that
this is the problem that you are running into. If so, it is easily
corrected.

Good Luck. Harry C.
 
Are you using a 'single point ground' for all the equipment, or a
multi-point grounding arrangement?

If you are using a multi-point ground for the different pieces of
equipment, you could very well be seing the results of a "ground loop"
causing a.c. current to flow between the the shields/commons of the
cables connecting your various units and an a.c. offset voltage
appearing in series with each of the signal lines.

Given the symptoms that you've posted, I'm inclined to believe that
this is the problem that you are running into. If so, it is easily
corrected.

Good Luck. Harry C.
 
Hi,

I was using a single 120 volt wall outlet to power all the equipment
when I first experienced the hum. That outlet is properly grounded
through the house wiring to the power panel. Both the satellite
receiver and the PVR computer are connected to a Belkin UPS that plugs
into the 120 volt outlet.

I did introduce a second ground with the satellite dish and cable being
grounded via the 4 foot copper grounding rod. i did that to provide
lightening static discharge protection for the satellite dish.

I'm guessing that second satllite dish ground was causing the hum - and
now I need to know if I should disconnect it - and run a ground wire
around the outside of the house to connect the dish and cable to the
house ground. I kind of think that is what I should do to avoid future
problems - although right now the hum has gone away!!.
 
Cindyane, it sound's as though you now have a handle on the problem.

A possible solution would be to float the ground connection on all of
your components, then tie them together and ground them to the antenna
ground. This would give you a single point ground for your entire
system, of course assuming that your antenna connects to a properly
driven and tested earth ground, and not simply a short length of copper
pipe driven only a foot or two into the earth. (One of those copper
plated ground rods sold at places like Home Despot should do the job
for you, provided you can drive 5 or 6-ft of it into the earth, and the
subsoil is moist.

As an aside, ground loops are very problematic when you are feeding an
outdoor circuit from a ground fault circuit breaker in the main
distribution panel, because of the temptation to locally ground hot tub
pumps locally for safety. This is because the ground fault breaker
usually wants to be the only point in the entire circuit having a
ground connection (for valid reasons). Many folks will try ground
both ends of the circuit thinking that it will improve safety, but with
the result that nothing will then work because the GFI immediately
opens the circuit.

Harry C.
 
J

Jon Elson

Jan 1, 1970
0
Hi,

I was using a single 120 volt wall outlet to power all the equipment
when I first experienced the hum. That outlet is properly grounded
through the house wiring to the power panel. Both the satellite
receiver and the PVR computer are connected to a Belkin UPS that plugs
into the 120 volt outlet.

I did introduce a second ground with the satellite dish and cable being
grounded via the 4 foot copper grounding rod. i did that to provide
lightening static discharge protection for the satellite dish.

I'm guessing that second satllite dish ground was causing the hum - and
now I need to know if I should disconnect it - and run a ground wire
around the outside of the house to connect the dish and cable to the
house ground. I kind of think that is what I should do to avoid future
problems - although right now the hum has gone away!!.
Unfortunately, some things trump hum, and electrical safety is one.
The outside ground rod is to absorb induced currents from nearby lightning
strikes, and to at least give your home a chance to survive a direct
lightning
strike without burning to the ground, electrocuting anyone or blowing
a 3 foot hole in the wall. You absolutely should NOT disconnect it!
(I'm not sure a 4' rod is really adequate, either, it depends on the soil.)

Since the hum is GONE, it seems to indicate a poor connection at the coax
connector. If the hum returns (could take a week, could take 2 years) you
now know to immediately disconnect and reconnect the coax cable and
it should hopefully go away again. If it returns too often, you may need a
new connector, cable to the sat. dish, or something like that.

Jon
 
W

w_tom

Jan 1, 1970
0
To understand your problem, first you must understand what
Charles posted:
1/ Grounds are not all the same. When two grounds are connected
together, a current can result (and often does). This current
can induce a hum signal into low-level signal conductors.

Lets example this. Take a radio connected to a long wire.
Radio receives signal. Ground the far end. Why does the
signal not disappear? Because wire is not a perfect
conductor. Ground at one end of the wire is not ground at the
other end. You have not yet understood that.

The way I read it, you have grounded satellite system to an
earth ground. They and a Belkin UPS are also grounded it to a
safety ground - wall receptacle. Meanwhile, computer and
other components are connected to another wall receptacle - a
completely different ground. IOW you have classic ground
loops. Numerous grounds - none that are considered a single
point ground.

Let's assume satellite wall receptacle and computer wall
receptacle connect at the breaker box single point ground.
Now you have a voltage between computer and satellite
equipment. That's right. Just like with the antenna.
Neither are fully connected to breaker box ground AND both are
even farther apart (electrically). That is the classic ground
loop problem.

Meanwhile, four foot earth ground is typically too short for
electronic protection. Also never remove safety grounds to
fix the problem. Reroute them? Ok. But those who fix
problems without first learning the problems will even solve
problems by disconnecting the human safety ground. Not
necessary nor advised if concepts of ground loops and single
point ground are understood.

Meanwhile, every wire entering the building - AC electric,
phone, CATV, and that satellite must share a single point
building ground. That four foot rod should be connected to
household ground by a buried, bare copper wire (as detailed by
NEC).
 
To clarify - the two satellite dishs and associated cables are
currently grounded with a Radio Shack 4' copper grounding rod driven 4'
into the ground - right underneath the satellite dishes. The satellite
cables run through a set of cable grounding blocks (which are connected
to the grounding rod). Those grounding blocks are located under the
roof eaves 5' away from the cable entry point to the home.

All the inside A/V equipment (satellite receiver, PVR, audio amplifier)
are connected to a Belkin UPS. The UPS in turn is plugged into a wall
electrical outlet that has a ground to the house circuit panel.

ok - So if I get this right - I need to interconnect the house
electrical ground to the existing 4' deep copper ground rod system I
have in place for the satellite dish and RJ6 cable.

That way - if lightening hits the dish - it (may) decide to run to
ground using the 4' deep ground rod right below the dish. If static
builds up on the dish - it can drain off either through the 4' deep rod
or to the house electrical ground. ... and the hum should go away.

By the way - the hum came back recently & we tried unscrewing and
re-connecting the Co-ax connectors & it did not go away. We ended up
connecting the downstairs PVR to another satellite lead (we have 2
dishes on the roof with 2 cable leads each) & that fixed it.... so far
anyway.

To do the ground interconnection you suggest bare copper ground wire.
I'm guessing that is to ensure good conductivity and the better
capacity of that wire to take a lightening hit? If that is the case -
should I not also replace the existing aluminum ground wire from the
copper ground rod running up to the dishes?

As an aside - I wonder why they even sell the aluminum grounding wire
if it is not up to the task. One thought is that it is meant for
static discharge only & not for lightening hits.

I would run the copper wire around the house up to an outside copper
water tap & use a bonding clamp to attach it to the copper water pipe.
Total run distance is about 30 feet.

I was planning on mounting it just under the house eavestroughs - or
does it have to go under the ground?

The existing house electrical ground wire is a 6 AWG bare copper wire
that runs from our power panel in the finished basement over to where
the copper water pipe enters the house foundation. Total run distance
for this grounding wire is about 50 feet.
 
W

w_tom

Jan 1, 1970
0
Yes, the cable incoming from dish must make a connection to
earth that is also the earth ground of every other incoming
utility wire. This 'single point earth ground' is required by
code for human safety AND also performed for reason not in the
code - transistor safety. This is also part of a system that
should make hum and static irrelevant.

The dish should be earthed directly. Also the incoming
cable from dishes should be connected to the single point
earth ground for reasons stated above. Since cable ground
block must connect to single point earth ground (which should
be at least an existing 8 foot ground rod), then two ways to
accomplish it. One is to reroute the incoming RG-6 so that it
enters the building and is earthed at the single point
earthing. Or expand the single point earthing using a buried,
bare copper wire (of size required by code) to include that
existing 4 foot earth ground rod. The second, if practical,
enhances what would otherwise be a minimally acceptable earth
ground.

That 6 AWG wire 50 feet long to water pipe is no longer
considered earth ground per post-1990 code. Again, that is why
the 'earthed at far end' antenna example was cited. That 50
foot wire removes electricity from water pipes as required by
code. But the earth ground must be, typically, an eight foot
ground rod located at the service entrance (ie outside and
adjacent to breaker box). Earthing connection that must be
many times shorter than 50 feet. The code is quite specific:
Article 250.52(D)(2)
Supplemental Electrode Required. A metal underground water
pipe shall be supplemented by an additional electrode of the
type specified in 250.52(A)(2) through (A)(7).

The eight foot ground rod is one of those acceptable earth
grounds in sections (A)(2) through (A)(7). Of course multiple
ground rods spaced per code requirements makes an even better
earth ground.

All other incoming utilities (telephone, cable) must connect
to that ground rod by less than 20 feet of wire. And then
more parameters, so that earth ground also provides transistor
safety. Every wire connecting to that earth ground must not
be bundled with other non-earth wires, must have no sharp
bends, no splices, must not connect to other earthing wires
until all meet at the ground rod, must be as short as possible
and 'less than 10 feet', and must not pass inside conduit or
other metallic item. A buried ground wire connecting to that
four foot rod would make that other earth ground part of the
single point earth ground AND supplement the effectiveness of
earthing.

For example, the #6 AWG wire from breaker box to earth
ground rod is better routed through foundation at least six
inches about outside soil rather than up over foundation,
through 2x10 wood, and back down to earth ground. Distance of
and routing that earthing wire away from other wires is for
transistor safety.

Connecting any wire to water pipes or faucet to establish a
ground is wrong - long time not acceptable. A simplified
version of the rule. Wire is connected to pipes only to
remove electricity from those pipes. That is what the 50 foot
wire from pipe to breaker box does - remove electricity -
especially to trip a circuit breaker if necessary.

Furthermore, the proposed 30 foot connection is even longer
because faucet's water pipes add more distance, solder joints
make that distance electrically longer, and sharp bends make
it electrically further. Again, return to that example of a
radio antenna earthed at the far end. Earthing did not affect
a radio signal because wire distance is critical for some
types of electricity. That 30 feet plus to earth ground
violates National Electrical Code (NEC) requirements AND so
long as to be not earthed from a perspective of transistor
safety.

And you thought grounding was so simple. We are discussing
earth ground; have neither discussed breaker box safety ground
nor that UPS ground. Those are other grounds. And then there
is bonding to the water pipe. Just another type of ground. A
safety ground which is why code uses the word 'bonding'; not
earthing.

A figure from a utility demonstrates the bad, good, and
least ugly ways of accomplishing a single point earth ground:
http://www.cinergy.com/surge/ttip08.htm

Notice how all this grounding forms a hierarchy. Earth
ground in turn meets many other grounds at a common point.
Interconnection grounds at the same 'level' can cause other
problems such as ground loops and hum.

Aluminum wire takes special consideration. Do not connect a
copper item to an aluminum wire. Special connectors are
required when aluminum connects to copper. The dish ground
wire, whatever it is, should make a shortest path from the
dish to earth ground.

Still this is only to meet code, protect humans, and protect
transistors. We have not yet addressed ground loops that
would cause hum.

Lets make that Belkin UPS to local single point ground (not
to be confuse with a single point earth ground or the single
point safety ground that is neutral bar inside breaker box).
Everything connected to audio amplifier (satellite receiver,
PVR) connects to same ground provided by the Belkin. IOW
there is no other incoming cable from any other electronics
that also connected to a household ground anywhere else?

For example, two receivers connected to two different
household grounds. Yes, both connect back to the same breaker
box. But that is long wire. The household ground in the
entertainment room remains different from the ground in
kitchen and from ground in basement. Again, remember that
radio antenna earthed at its far end.

If two different receivers are electrically grounded via
cables to the same dish, now we have a ground loop. That
ground loop may or may not create hum. The single point
ground for equipment common to the Belkin must never connect
to the equipment common of satellite receiver in the
basement. Those grounds must remain separate until both meet
at the breaker box ground. Again, that hierarchy. Otherwise,
a ground loop exists and may create hum.

Electricity at one end of a wire is not same as electricity
at the other end of same wire. Which is why to take care
about single point grounding of equipment AND then single
point grounding all those single point grounds to a building
wide single point ground such as the breaker box. Even water
pipes make a separate connection to that single point breaker
box ground. And that breaker box ground, in turn, connects
where all other earth grounds connect - at a single point
earth ground.

It is quite possible that once you get all satellite cable
grounds directly connected to same earth ground, then single
point earthing eliminates the hum. We will not know until
that single point earth ground is created. IOW start and
correct at the single point ground that is for every ground in
the building - earth ground. And then we move down the chain
of grounds making sure that each next level ground (breaker
box ground, wall receptacle ground, etc) only connects to a
higher level single point ground. Single point ground at
each level for numerous reasons including hum created by
ground loops.

There exists so much in this post that you should read it
multiple times. Welcome to the artistic side of grounding.
 
My eyes are spinning......

I have contacted my electrical utility to ask about the ground - as it
may be they have a ground rod near the breaker box that I do not know
about. By the way - we have underground wiring.

Can you tell me if I have this right?
* I should have an 8' ground rod as close as possible to my breaker box
to meet curent code requirements. That rod should be connected to the
breaker box with 6 AWG copper wire less than 10 feet in length. Cable
and phone grounds should be connected to this wire.

* I can leave the existing 6 AWG ground wire that currently runs 50' in
our basement from the breaker box to the water inlet pipe as that
(although insufficient for todays code) still adds a little to the
ground - and serves to ground the water pipes.

When you said "the dish should be earthed directly" - I initially
thought you meant I should pound an 8' ground rod below the dish and
run 6 AWG from the dish to the rod. But now I think you mean the
following:
* I should run 6 AWG bare copper wire from the 2 satellite dishes down
through the CO-AX grounding blocks and attach it to the existing 4'
copper ground rod located under the dishes and then run the wire buried
under the ground by a foot or so right back to the 8' grounding rod
(the one I might have to install) beside the breaker box. Total length
for this run is going to be around 60 feet.
 
W

w_tom

Jan 1, 1970
0
Point 1) Yes that 8' ground rod near the breaker box with
connections to phone and cable grounds is required to upgrade
your earthing; to meet post 1990 NEC requirements. A second
ground rod spaced sufficiently distant or buried ground wires
to other earth ground rods would enhance the quality of that
earth ground.

Point 2) yes that 50 foot 6 AWG wire to water pipe is
required by code to 'bond' water pipes - essential for human
safety. When you say 'ground water pipes' - a general term -
what you really mean is 'bond' water pipes to breaker box
safety ground. Bonding being only one type of grounding.
Connection to water pipe should be as close as possible to
where pipe enters the building.

BTW, a bypass ground from one side of water meter to the
other is also required - for human safety. And a ground wire
above hot water heater from incoming cold pipe to outgoing hot
water pipe may also be required. Some local jurisdictions
also require a ground wire from metal bathtubs to the breaker
box safety ground. These, of course, are well beyond and
would not solve your original problem. This paragraph is
sidebar information.

Point 3) preferred way of earthing the antenna (or dish) is a
wire directly down to an earth ground rod. A second ground
connects coax ground block to single point earth ground where
that cable enters the building. A direct strike will mostly
take the shorter path to earth - down the shortest wire from
antenna / dish directly to earth. Other transient currents
would be earthed at the single point earth ground; before that
coax enters the building. See 'General Point' below for more
details.

Yes, I meant "pound an 8' ground rod below the dish and run
6 AWG from the dish to the rod." And the other ground
connects coax to single point ground where coax enters the
building - a location called the service entrance.

Technically, an earth ground rod directly below the dish
should also connect to the single point earth ground by a
buried bare copper wire as demonstrated by that cinergy.com
figure. This would both enhance the earthing system and
better meet code. But for transient protection, that wire
from dish both short and direct (as is feasible) to earth is
important for transient protection (and does not address your
hum problem).


General point) That single point earth ground rod -
household earthing - is 'secondary' protection. If utilities
were from overhead wires, then inspection of 'primary'
protection system would also be necessary:
http://www.tvtower.com/fpl.html

Even buried wires can carry destructive transients into a
building. Buried or overhead, any incoming wire must first
connect (either by hardwire to ground block, or via a surge
protector) short to the single point earth ground. This figure
demonstrates the concept:

http://www.erico.com/public/library/fep/technotes/tncr002.pdf

Note that diagram. The building has a single point ground
and the tower has a single point ground. Each are treated as
separate structures. Basically you are doing same. Also note
the interconnected and buried ground wire from building single
point ground to antenna tower single point ground. That
interconnection, among other advantages, enhances both
earthing systems - mostly for transient protection.

Again, all this mostly does not address your hum problem.
But having every utility and your 'breaker box safety ground'
all connected to a single point does contribute to hum
reduction. Therefore no ground loop should exist inside your
building from utilities carrying different noise voltages. If
noise voltages on each utility are same, then noise from this
source is less likely to adversely affect household
electronics.

Your electric utility has no obligation for your household
ground. That building earth ground is completely your
responsibility as defined by National Electrical Code.
Therefore either you or your agent - the electrician - solves
your household grounding. Utility grounds are exampled in
pictures above from tvtower.com . The only exception might be
how your gas utility wants their pipes connected to your
household ground system. Different gas utilities have
different requirements.

The word 'ground' confuses. There is bonding, earthing, and
grounds on your motherboard and computer chassis, and another
ground beneath shoes when discussing static electricity.
Different types of grounds that are interconnected. Each for
different problems - have different characteristics - and
often share many components.

Even the ground between adjacent components at your
satellite receiver, Belkin, and audio amplifier are but
another ground - a ground to eliminate ground loops and hum.
A ground that those electronic appliances share at a single
point, AND a ground that must then connect to other single
point grounds such as breaker box safety ground and building's
earth ground.

Confused? I can very much appreciate it. Actually, many
electricians don't understand all this. Electricians are
still trained mostly in concepts only for human safety. But
with transistors for 30 years, these more advanced grounding
concepts that were standard in buildings such as telephone
switching centers and commercial broadcast centers also need
be installed in homes - using these simpler, less expensive,
and less comprehensive methods.

The electrician will understand why things must be bonded.
That is human safety. But many (including cable and telephone
installer) still do not understand electronic or RF reasons
why grounds must be shorter - such as 'less than 10 foot', no
sharp bends, separated from other wires, etc. The transistor
have made building grounding important. We still don't build
new homes as if the transistor existed. So we install a
kludge solution as described above and unfortunately, when it
is more difficult to install. Unfortunately, that means
homeowners are stuck trying to learn concepts that
electricians, builders, and architects should have known 30
years ago.

The single point grounding techniques installed building
wide for transient protection as similar to the single point
grounding done at the entertainment center to eliminate hum.
All those single point grounds contribute to make the others
more effective and functional. They all solve ground loop
problems.
 
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