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Grounding / Earthing. What does these lines mean?

Discussion in 'General Electronics Discussion' started by Azee, Aug 20, 2012.

  1. Azee

    Azee

    5
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    Aug 20, 2012
    Hello Everyone,
    I have a 5 ampere weighing equipment & need it to ground properly. It is about 80 feet away from soil point. (Direct wire to the equipment will be used & long term connection is required).

    Manufacturer says that:

    "There must be a good third wire ground, preferably to a true ground or ground rod. Then check the resistance to that ground to all the contact surfaces of the equipment. There should be 0 ohms resistance since the static generated by the motion of the product needs a place to go".

    1: What metal rod/wire or some thing else will be enough to use to vertically or horizentaly drive in soil. Length + diameter & other specifications. What size device will work in this case.
    I need to be much closer to 0 ohms resistance. This is the actual target.
    I can have digital clamp meter which have 200, 20k, 20M & 2000M ohms options.

    2: Green (Ground) wire of the equipment is still to be ground as there is no ground connection to the wall socket.
    Shall I need two rods?
    First to connect with green wire & the second to connect with equipment's metal frame?
    Or the same rod will be used to connect Green wire & Metal Frame?

    3: For my reference please inform after grounding Green Wire & Metal frame how I can check resistance just like one can check voltage readings with a meter in hand by using probes. Please inform step by step.
    Means to say how i can say or proof that resistance to the ground to all the contact surfaces of my equipment is 0 or any other reading that displays.

    Thanks in advance.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,131
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    Nov 17, 2011
    1) use a ligthning rod, that should be fine. You won't achieve "0 Ohm", that's impossible. You can come close. Less than 1 Ohm should be o.k. Use the 200 Ohm range of the meter to check.

    2) I can't tell for sure about the "green wire" but it sounds (from your explanation" as if this wire could be connected to the same ground rod as uised in 1).

    3) Make sure the equipment under test is not powered (power to the equipment can lead to the meter giving false readings). Set the meter to Ohm. Press the tip of probe 1 to the first connection, tip of probe 2 toii the second connection. The meter will show the resistance between the two connections.

    My suggestion: have an electrician do the installation. He knows how to make it safe.
     
  3. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    In my area they use 5/8" copper clad steel rods, 10' long nailed straight into the ground to a depth of at least 8' for residential use and usually a 3/4" diameter 10' long rod for commercial... Many times there will also be a jumper made to the metal water service pipe as well to act as a backup ground...

    Consult your local electrical code for specifics...

    Many times it's bare wire, not insulated for the connection to the rod, again in my area this wire is usually dropped through conduit to keep it tidy, not fully piped in the conduit, the conduit is just use to tidy it up and provide 'security' from it getting unconnected... And again in many cases they bond the ground wire to this conduit sleeve for even more redundancy...

    This ground wire is again 'in my area' of equal gauge (sometimes dropped one gauge) from the supply lines required/specified handling capacity...

    Consult your local electrical code for specifics...

    To check for proper grounding, negative probe on ground wire and positive probe on the supply wire(s), it should meter out at your full supply voltage if the ground it good...

    And in case you missed it...

    Consult your local electrical code for specifics... Or better yet consult a professional in your area...
     
    Last edited: Aug 20, 2012
  4. Azee

    Azee

    5
    0
    Aug 20, 2012
    How to check ohms resistance in this case?

    Hello Everyone,
    I have to check / read the ohms resistance on clamp meter.
    How i will do it in below case. Please tell step by step.
    1: I have driven 8 feet copper rod in the ground.
    2: I have connected First End of each seperate cable to this copper rod. Here I name it as Cable A & Cable B.
    3: I am going to connect the second end of the Cable A to Green Wire (Ground / Earth wire) of the power supply cord of machine to establish main / basic / substancial ground connection.
    4: I am also going to connect the second end of the Cable B to the Metal Frame of the same machine to establish Extra / Secondary ground connection too.

    5: If it is justified or practically viable to have two seperate earthing wirea to be connected to same machine as i need powerfull earthing.
    6: At which point I can check ohms resistance with a clamp meter. Which are the wires to which the probes of clamp meter will be touched to have ohms resistance readings.
    Awaiting reply.
     
  5. davenn

    davenn Moderator

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    Sep 5, 2009
    you can read Ohms with a clampmeter UNLESS the meter has sockets for normal leaded probes

    Dave
     
  6. shrtrnd

    shrtrnd

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    453
    Jan 15, 2010
    I don't know where you're at. I live in the desert. We typically install a ground rod horizontally, and have difficulty GETTING a good ground, because the soil is so dry.
    (The actual 'ground' value changes with moisture in the soil).
    For your reading, it would help if you told us the make and model of the meter you're using.
     
  7. Azee

    Azee

    5
    0
    Aug 20, 2012
    I have this clamp meter as linked below:

    http://www.bizrice.com/upload/20120322/AMPD_266_DT266_DMM266_digital_clamp_meter.jpg

    I am in punjab India & there is no problem in getting good ground round here. I have no idea that how to use this clamp meter but my target is to get very low resistance to proof manufacturer that I have very low ground resistance now.

    Manufacturer of machine says that:

    "There must be a good third wire ground, preferably to a true ground or ground rod. Then check the resistance to that ground to all the contact surfaces of the equipment. There should be minimum acceptable ohms resistance since the static generated by the motion of the product needs a place to go".

    I have to check the resistance as manufacturer has aledged to let them know that the resistance is some where very close to 0 ohms.
    Awaiting reply.
     
    Last edited: Aug 21, 2012
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    9,131
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    Nov 17, 2011
    The clamp is for measuring currents only.
    For measuring resistance you have to connect probe wires to the terminals at the bottom of the meter. The terminals are labeled VΩ and COM.
    Turn the range selector to the 200Ω range (9 o'clock). Test the setup by touching the probe tips. The meter should read <1Ω.
     
  9. davenn

    davenn Moderator

    13,242
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    Sep 5, 2009
    Azee

    I have to comment, Your thread on this exact same topic was locked in another forum, because it became very obvious that you didnt really know what you were doing, and messing around with mains powered systems if not for the untrained

    It was there suggested to you that you employ the services of a qualified electrician to do this work for you

    I will await a response before closing the thread

    Dave
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    I am pretty sure that the reference to zero ohms is a reference to the resistance between the equipment and the earth connection, not to the soil (or whatever).
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

    9,131
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    Nov 17, 2011
    @steve:
    That should read "you can't"

    But I agree: employing an expert would be his better option.
     
  12. Azee

    Azee

    5
    0
    Aug 20, 2012
    Thanks a lot.
    I have connected Cable A to green wire in machine's power suplly code & Cable B to one of below four components.

    Please tell what do you mean by
    "Test the setup by touching the probe tips".

    Do you mean different parts of the machine? Machine has hopper, weight bucket, load cell & feeder pan as it is a weighing scale.
    You mean i have to touch each component with each of remaining components one by one? For example touching hooper with one probe & other to remaining three components with other lead. Am i right?
    If so i have checked it & it fluctuates in between 00.8 to 01.3
    Is this the actual ohm reading?
    Thanks.
     
  13. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Yeah, that is why I specified what they do for 'my' location, every location is different and thus my suggestion to consult local codes... I hear it's common practice in dry locations to ground all the reinforcement metal inside the concrete foundation and thus get a larger surface area for ground since this results in the entire concrete foundation becoming a ground plain...
     
  14. Axel87

    Axel87

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    Aug 18, 2012
    I 2nd employ a service professional. Sometimes time and energy can be more costly in the end. If instead you let the pros hook you up, life may get a little easier.
     
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