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Wierd Ground Problem?

Discussion in 'Misc Electronics' started by [email protected], Nov 2, 2005.

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  1. Guest

    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
     
  2. 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.
     
  3. Guest

    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.
     
  4. Guest

    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.
     
  5. Guest

    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!!.
     
  6. Guest

    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.
     
  7. Jon Elson

    Jon Elson Guest

    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
     
  8. w_tom

    w_tom Guest

    To understand your problem, first you must understand what
    Charles posted:
    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).
     
  9. Guest

    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.
     
  10. w_tom

    w_tom Guest

    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)
    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.
     
  11. Guest

    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.
     
  12. w_tom

    w_tom Guest

    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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