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Thread: Earthing terminology - LNB and Dreambox

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    Default Earthing terminology - LNB and Dreambox

    So I've read the thread on earthing your dreambox. Read it twice actually. I understand I have to earth my dreambox and I'm going to run an earth wire from the power point to the casing of the box.

    My problem is some people talk about earthing their LNB. Is this one and the same as earthing the dreambox? If not, can someome please point out the difference.

    Thanks



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    Casing of the box is connected to the LNB via the coax. Hence earthing the box is enough from what I heard and learnt.

    I posted pics of what I did with my dm-500 on one of the threads...

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    Yes, you are on the right understanding. It kind of gets tricky at this point.
    When the RG6 is screwed into the box, yes everything is earthed, but when you remove the RG6 which bit shall remain at earth potentional?
    Should you earth the box chassis or the RG6 metal crimp or wall plate?
    Must How To's show the Wall plate female barrel connection being earthed, and i would suggest this to be the prefered method.

    You need to ask yourself, where is difference in voltage going to come from? Will the non earthed chassis of a SMPS unit let it raise above ground or is the RG6 LNB cable more likely to come into EMF interferrence or induction and rise above ground?
    I say this because a lot of people swap LNB leads with the STB power still on.

    Or should you earth both? There are reasons for and against all of these options.
    Just earth the RG6 wall socket and you should be fine

    The most dangerous part in all of this, is you grabing an earth from a power point. People have over come this by making a 3 pin lead with ONLY!!!! the earth conductor connected.

    And at the end of the day, if you follow safe and smart practises, you really shouldn't need to earth it at all. But it's better to be safe than sorry

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    Ahhhh... I think you just shattered by potential solution.
    I'd better get this right first. I'm considering 2 options:

    1. I buy a power point plug, with 3 pins, and just wire an earth wire from the casing of the box to the earth pin on the new plug. So I would actually have 2 power points used by the dreambox. 1 for the real power and another is my made up plug with 1 wire from earth in the socket to the casing.

    2. I cut the dreambox 2 pin power point plug off the end. Then I wire the positive and neutral into a new 3 pin plug. While I'm there I connect an earth wire to this new plug and screw the other end of the dreambox case.

    Oceanboy - from your comment it sounds like option 1 is really bad?

    Which one is the best option?

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    Option 3: Turn the power off to your house, remove the PP and STV outlets from wall, supply and fit crimped lug on back STV connecetion with lock nuts, connect other end to earth terminal of pp. Fit both units back to wall and you done!

    Of coarse i always recommend using a Licenced Electrical Contractor for such work

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    OK from an electricians point of view.

    the standard in Australia is to have a MEN - main Earthed Neutral system. This is where the main Earth of your house is connected to the Main Neutral Link, the Neutral out on the street is earthed as well. As electricity that flows through an appliance comes back to the Main Neutral as this is the return path of the electrons to an Earthed state (as everyone knows - shortest path to earth.) The Main Earth is to remove short bursts of energy such as a dead short (knife into toaster touching the stainless steel bit)

    So to the question that has been asked here.......earth the box or the coax - it doesn't matter what you earth because the connection of the crimp will earth whatever is connected to. That is if you earth the box - then when you connect the LNB to it - the shield on the coax is earthed too. If you earth the coax at the wall then when you connect it to the box - you guessed it........earthed too. Don't forget all you are doing is making the Box or coax to the same potential of your earthing system in your house - if that is 50 years old and you have had dodgey brothers in to do a cheap job then you could have a small issue of 240 volts on the box when / if your neutral & earth fails

    more to ponder over............

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    Its not shortest path to earth, length has nothing to do with it. It's the path of least resistance.
    An earth is there to remove shorts bursts of energy?
    I thought it was there to as a second fault current path to activate a circuit protection device or RCD?

    As for it doesn't matter what you earth... the point of this exercise is not to enable an RCD or MCB to activate, it's about small amounts of potiential difference that may spike sensitive components onboard the Dreambox, yes?

    Thus there is a fair chance damage will occur during the disconnection and/or reconnection of the LNB cable, it's hardly going to come from the 240v side.
    It can even come from RCA leads that are connected to a Receiver. or just static charge.... So what do you earth now?

    But yes, you're right, for the most part, the LNB cable will be connected, thus earthing the Chassis and the RG6 Coax shield to the same potential and HOPEFULLY providing a fualt current path of least resistance to somewhere other than a cap jump to neutral within the box itself

    Thats my understanding anyway.... Maybe i'm wrong?

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    Quote Originally Posted by oceanboy View Post
    Its not shortest path to earth, length has nothing to do with it. It's the path of least resistance.
    spot on - wrong terminology, sorry

    An earth is there to remove shorts bursts of energy?
    I thought it was there to as a second fault current path to activate a circuit protection device or RCD?
    sort of.....a rcd is a device that measures the current that flows through the active conductor and returns through the neutral and any difference is assumed a fault

    As for it doesn't matter what you earth... the point of this exercise is not to enable an RCD or MCB to activate, it's about small amounts of potiential difference that may spike sensitive components onboard the Dreambox, yes?
    yep spot on!

    Thus there is a fair chance damage will occur during the disconnection and/or reconnection of the LNB cable, it's hardly going to come from the 240v side.
    yep - 99% right - induced voltage.........but that is so far out there....


    It can even come from RCA leads that are connected to a Receiver. or just static charge.... So what do you earth now?
    I spose you can assume the person playing with the dream has no intention of connecting / disconnecting / connecting / disconne.............

    But yes, you're right, for the most part, the LNB cable will be connected, thus earthing the Chassis and the RG6 Coax shield to the same potential and HOPEFULLY providing a fualt current path of least resistance to somewhere other than a cap jump to neutral within the box itself

    Thats my understanding anyway.... Maybe i'm wrong?
    ahhh great minds think alike......you definitively have a good grasp


    f

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    oceanboy - this your your comment that has confused me:
    "The most dangerous part in all of this, is you grabing an earth from a power point. People have over come this by making a 3 pin lead with ONLY!!!! the earth conductor connected."
    Think I'm mis-interpreting this as the first and second sentence seems to contradict each other. The first sentence says it's dangerous to grab earth from a power point and the other says people do this?
    Isn't this one of the options that was proposed above?

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    Sorry mate, the danger is "in the doing of it" as some people maybe not isolate the power to the power point, so they may get a shock. I was suggesting the wiring is all done BEHIND the wall (neater) so you are playing where you shouldn't be. Making a 3 pin plug, is getting around the AS3000 rules as it is NOT fixed wiring.... Thus any squid can do it

    It is said in the context that, you are probably more likely to hurt yourself whilst attempting to earth your dreambox, than anything EVER happening to your dreambox if you had just left it alone

    aka you need to know what you are doing, even though it is very simple for people that do.

    Personally I don't like the idea of earthing it the house earthing system, there is more chance of a fault current coming down that path than anywhere. I have installed brand new Fujitsu Air Cons that have +60V ac returning on the earth conductor whilst running (measured whilst lifted from the earth bar, and it gave you a belt in the hand too, not just some phantom voltage) So if anything were to happen to your earth stake connect, what then?

    It would be ultimate to drive a separate earth stake in the ground just to earth your AV stuff. But then people are going to say "What about earth loops"

    Probably running a 6mm Earth cable direct from your Switchboard Earth Bar to a Small Earth bar mounted on a Blank Plate behind your Stereo gear is the best compromise. Providing a very low resistance path to ground.

    At the end of the day, there is no perfect answer, is I mentioned in my fist post. DMM have recommended the "earth the STV wall socket from the nearby power point method" so I guess that’s what you do.
    Last edited by ol' boy; 18-04-08 at 11:40 AM.

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