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Some help with grounding my welding table (Ideas please)

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  • #16
    The table should be grounded. If your cable you have clamped to your table should fail or come apart from the table and you are touching your work piece.... you are at risk of completing your weld circuit (getting zapped).
    Grounding the table isn't going to help this.
    The weld table is portable in that it has wheels that do not conduct electricity (table is never grounded), otherwise the legs sitting on the ground might offer some protection.
    I see we are still stuck on what grounding actually is and does, pounding a rod for this table doesn't protect you from anything. None of it will protect against shock from output of welding machine and the only thing that protects from AC current is a ground wire back to service main.

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    • #17
      "Section 250.4(D) (5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path." This section requires a low impedance fault return path. The only way to achieve this is to have the equipment ground wire in the same cable, or raceway with the circuit conductors. You cannot separate current flow and maintain a low impedance, it is impossible. Notice one more thing in the above statement. The fault return is go back to the electrical supply source, not where else.
      Where do we ground equipment? And yes, electronic equipment is equipment under the code and must comply with all the rules. I know some electronic people think they are special, and are exempt from certain aspects of the code, but believe me they are not. They must follow the same rules as the rest of us. Section 250.6(D) contains the following statement: "(D) Limitations to Permissible Alterations. The provisions of this section shall not be considered as permitting electronic equipment from being operated on ac systems or branch circuits that are not grounded as required by this article. Currents that introduce noise or data errors in electronic equipment shall not be considered the objectionable currents addressed in this section."
      This next section tells us what we are to ground equipment to. Believe it or not, no equipment goes to a ground rod, and no equipment whatever is ever connected to a ground rod to ground it. (Yes, there is an exception for 'supplemental grounds') Section "250.4(A)( (3) Bonding of Electrical Equipment. Non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path." The electrical supply source is the system from which the circuit originated, actually the supply neutral.
      Remember this statement: When the code requires a piece of equipment to be grounded, it is grounded (bonded really) to the system grounded circuit conductor, the neutral. It is never connected to a ground rod, a water pipe, building steel or anything else. It goes directly to the system grounded circuit conductor. (in the case of delta systems it goes to the grounded service equipment).
      Then, we ground the system grounded conductor, the neutral, to earth, no equipment to earth, the system neutral to earth. Stop for a minute and consider where you put all the equipment grounding conductors at home. Most of you wired with Romex and the bare ground is landed directly on the neutral bar in the main service disconnect. Not in a subpanel, but at the main itself. Then you grounded the neutral. Thus all the equipment in you house is grounded to the neutral, just like is supposed to be.
      Remember this also, the code requires a low impedance ground-fault return path for fault current. In order to obtain this, we must keep all the circuit conductors and the equipment grounding conductors in close proximity in the same raceway or cable. The is also required in "300.3 (B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4)."

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      • #18
        Section 250.54 allows for what the code calls "supplementary grounding electrodes". Some electronic equipment in the installation instructions require this electrode. Why they want these I have no idea, but some electronic people think that if it isn't connected to earth, then it isn't grounded. They don't understand that the earth is loaded with stray currents from many things, but so be it. These stray currents come from many sources. One is the fact that between your grounding electrode at home the system transformer, there are currents through the earth in parallel with your service neutral. These are a fact of life and how much current depends on a lot of things. Also, you, or your neighbors could have a piece of UF going out to a yard light that has a nick in the insulation. Black or white, it don't matter. Some current is leaking out of this nicked insulation and will find it's way back to the electrical system through the earth. Then there are the installations that now grounded to a ground rod because that is the way they were put in. A good example of these are mall parking lot lights, or any large area lighting. A lot of these have no ground wire to them, they are grounded by way of a rod. If one of these lights develops a ground-fault, the current flow is down the rod, then back to the source through the earth. There are many references in the code that prohibit using the earth for an equipment grounding conductor, but these installations exist by the hundreds. If a ground rod is driven into an area that has any of these conditions, the current will be imposed on the equipment connected to this "isolated ground rod". This creates a shock hazard when touching the equipment grounded this way, and any equipment in the building that is connected to the building grounded system.
        Take at least one example: A piece or equipment is grounded to a ground rod to satisfy the electronic people. They insist that the equipment be connected to an isolated ground. The average ground rod will megger well over 100 ohms. But just suppose you are lucky and manage a 10 ohm ground rod. 120 volt divided by 10 means that leas than 12 amperes will flow in case of a ground-fault. Will this clear a 15- or 20-amp overcurrent device? No way, but there is 120 volts going down the rod, and 120 volts on the metal of the equipment, just waiting for someone to come in contact with it. Where is this current going from the ground rod. Pretty much where ever it wants, and if there is a swimming pool nearby that for some reason wasn't properly bonded, or has a bad bonding connection, this could be time for an electrocution. About the overcurrent device, in order to clear a standard 20 amp circuit breaker in a reasonable time, it must have close to 80 to 100 amperes pass through it. Kind of hard to do when the rod will only pass 10 or 12 amperes.
        I strayed, back to 250.54. This section permits a supplemental grounding electrode at the equipment, but the electrode must be connected to the equipment grounding conductor in the circuit to the equipment. A lot of mall lighting is installed this way. The supplemental electrode is bonded to the equipment ground of the light, and it provides added safety for lighting hits. A lot of the lightning energy will dissipate down the rod. Otherwise it would go back on the equipment ground in the circuit and since the insulation is only 600 volts, it causes a lot of damage to conductors.

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        • #19
          Get rid of the term "ground cable"

          Sberry

          Thank you for your in depth post. As a retired Coast Guard Avioincs Tech, I have to say that a large portion of Avionics failures had to do with mechanically poor, corroded or broken grounds or bonding wires. My first two troubleshooting steps were to 1)- check the fuse, 2)- check the grounds.

          Sberry also made made good points about stray currents. Stray currents bring up the possibility of difference of potential between two items on different ground systems. You can also have dangerous differences of potential on the same circuit between long runs of wire or between wire connections.

          My advise to Cyber Dolphin is; DO NOT GROUND YOUR TABLE. ie; Do not earth ground it separately as it will be at a different potential from your other electrically grounded equipment chassis. Do not electrically ground it to your electrical system.

          Since there is so much ambiguity between different meanings and incorrect interpretation of the term "ground", I thin the AWS should clarify the term and to get rid of the term "ground cable" in reference to the "ground" in the welding machine circuit. Maybe call it the "Work Plane Cable".

          As far as HF interfering with my electronics, I think my solution is to reexamine the 50 amp feed from the service panel to the welding machine outlet. It is the proper gage aluminum cable with I believe, a copper ground wire. A large portion of the run is between the studs without steel conduit.

          At some point you have to trust the engineers and electrical code and look for where your own mistake caused the problem.

          That being said, I think I'm going to make some kind of Faraday shielding around my all too expensive electronics in the shop.

          One final point. Since the electrical ground is tied to the neutral bus and the electrical ground is tied to most metal chassis and covers of electrical equipment, the metal chassis is essentially a bare exposed neutral (white) wire. This is my one disagreement with the electrical code. (While I disagree, I still follow it to the letter.)

          During a storm up here in the mountains, a hot wire fell and crossed to another phase. I heard the exhaust fan and light turn on over the stove while other circuits went out. I ran to shut down the breaker panel. Lots of people in the area lost electronic equipment.

          Once, an idiot mechanic at the marina decided to play electrician and hooked the hot wire to ground for the whole dock. He damaged lots of equipment and burned up numerous $$$ Heart Marine inverter/Chargers.

          Accordiing to NMMA, the negative DC leg of my DC Electrical system in my sailboat (36 ft live-aboard size) should be tied to the AC electrical system ground and by default the neutral leg of the AC system. There is no way I am going to work on my engine and put my body onto the other half of a live AC electrical system. I keep my AC and DC system electrically separate.

          This is the reason Cyber Dolphin should not electrically ground his table. But it makes me question any metal device that is electrically grounded, including the welding machine. The original intent of the ground circuit is protect you when a hot wire comes loose and contacted the equipment case ... but heck, you end up holding half a live circuit in you hand (thinking my father old metal Rockwell electric drill.)

          Comment


          • #20
            This is not my field of expertise so describing it could be a bit vague at best, much of it is over my head but,,, as for the neutrals being imposed on cases being grounded it isn't. We need someone here that can explain ground planes or what ever they call it, but at service neutral its grounded to earth, tied together, only way you get neutrals imposed on equipment is if it is in series with the wire and only as much voltage as the resistance of the wire provided it is grounded conductor, like you can touch a neutral bar in a system, no shock but at the end of a long run there will be some, there is no current flow on a ground wire except in the event of a fault.
            In the back of my mind somehow it all makes sense, wording it is another issue and not an engineer or even good electrician at that level. Only thing I get (which is now almost a reflex of sorts) is the correct install for the common equipment we use, thats really my only interest. I kind of dwell here as I can recall the things I didn't know, lack of understanding I had at one point that was crucial to legal installation.
            All this was explained to me at one time, not usually crucial to my work so I forget the details quickly.
            Last edited by Sberry; 11-14-2010, 01:59 PM.

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            • #21
              "If you are going to drive fifty new ground rods in the area, its ok, but they must electricly tie back to the ground bus or service entrance ground."

              Miller HF:

              The drawing is a basic drawing but I imagine they are assuming the reader that understands any of what is going on in the Drawing will be bonding all of the Metal back to the Service Entrance Ground and Neutral.
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              • #22
                Originally posted by Broccoli1 View Post
                "If you are going to drive fifty new ground rods in the area, its ok, but they must electricly tie back to the ground bus or service entrance ground."

                Miller HF:

                The drawing is a basic drawing but I imagine they are assuming the reader that understands any of what is going on in the Drawing will be bonding all of the Metal back to the Service Entrance Ground and Neutral.
                Not a good idea to assume the reader knows that. The reader is likely a weldor not an electrical engineer. Miller can easily draw it or include a note stating that all grounding electrodes need to tie back to the electrical service entrance ground.

                Comment


                • #23
                  Originally posted by joiseystud View Post
                  Not a good idea to assume the reader knows that. The reader is likely a weldor not an electrical engineer. Miller can easily draw it or include a note stating that all grounding electrodes need to tie back to the electrical service entrance ground.
                  They should probably not say anything in their manuals 'cept

                  "Hire an Electrician" you Weldors
                  Ed Conley
                  http://www.screamingbroccoli.net/
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                  • #24
                    Originally posted by cybordolphin View Post
                    I would like to ground my welding table (not just make it part of the weld circuit).

                    Please post your ideas and or pics of how you have your weld table grounded.

                    I am going to be welding in a solid concrete and cinder block enclosure (with windows). I can't easily drive a ground rod and tie to that. And I have no water pipes nearby. What other ways are there? I might be able to use a ground from the building circuit, but that is also the same ground as the weld circuit I believe.... so that might negate the whole idea/purpose.

                    The weld table is on wheels and I don't believe they conduct electricity. Thus I want to make sure the table has a good ground (don't want the ground to be "me").

                    Thanks for any input....
                    Just a simple clamp with wire going to any ground. The ground the electrical box is grounded to. Does not have to be complicated. Just a 12AWG wire. (Miller recommendation)
                    Last edited by Donald Branscom; 02-16-2011, 04:02 PM.

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                    • #25
                      Originally posted by Donald Branscom View Post
                      Just a simple clamp with wire going to any ground. The ground the electrical box is grounded to. Does not have to be complicated. Just a 6 ga. stranded wire.
                      From the Miller welding Manual for the Syncrowave 200.
                      Syncrowave 250 the same.

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                      • #26
                        Originally posted by kandrwelding View Post
                        Like most others im not shure why you would dothis but if I was going to do it I would rent a hammer drill from Home Depot and drill threw the floor to ground the table.
                        Make sure it's not a "Post-Tension" floor, otherwise you'll put yourself into orbit. Those cables have 15 tons of "pull" on them, and will literally "explode" the floor.

                        Granted, these types of floors are primarily used in siesmic zones, or areas of unstable soil, and out west, we have many readers............
                        "Bonne journe'e mes amis"

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                        • #27
                          Originally posted by cybordolphin View Post
                          I would like to ground my welding table (not just make it part of the weld circuit).

                          Please post your ideas and or pics of how you have your weld table grounded.

                          I am going to be welding in a solid concrete and cinder block enclosure (with windows). I can't easily drive a ground rod and tie to that. And I have no water pipes nearby. What other ways are there? I might be able to use a ground from the building circuit, but that is also the same ground as the weld circuit I believe.... so that might negate the whole idea/purpose.

                          The weld table is on wheels and I don't believe they conduct electricity. Thus I want to make sure the table has a good ground (don't want the ground to be "me").

                          Thanks for any input....
                          I would like to clear up some things about the grounding and the work table.

                          When you weld something you have a ground cable(work) cable from the welding machine that you attach to the weldment.

                          But if you are welding on a steel TABLE TOP and you have the weldment laying on the table top, you can attach the work or ground cable from the welding machine to the weldment directly. OR to the table top if it is a small weldment.

                          But if say for instance you are welding on that small weldment and you move it on the table top and if for a split second it does not get a good ground ,that is why it is good to have that ground cable attached to the table to protect yourself from becoming the ground.


                          Thats all this is about.
                          For HF that ground to the table helps stop HF from dancing all around you.
                          Last edited by Donald Branscom; 02-16-2011, 11:48 PM. Reason: spelling

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                          • #28
                            Originally posted by davedarragh View Post
                            Make sure it's not a "Post-Tension" floor, otherwise you'll put yourself into orbit. Those cables have 15 tons of "pull" on them, and will literally "explode" the floor.

                            Granted, these types of floors are primarily used in siesmic zones, or areas of unstable soil, and out west, we have many readers............
                            Good thing to keep in mind.
                            You can usually look at the outside edge of the foundation and see those steel cones connected to the cables.

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                            • #29
                              Originally posted by Donald Branscom View Post
                              Good thing to keep in mind.
                              You can usually look at the outside edge of the foundation and see those steel cones connected to the cables.
                              They're usually stamped, "Do Not Drill," but, yes, you can see the "snubs" around the perimeter of the slab.
                              Last edited by davedarragh; 02-16-2011, 04:30 PM.
                              "Bonne journe'e mes amis"

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                              • #30
                                Donald Branscom Quoted "But if say for instance you are welding on that small weldment and you move it on the table top and if for a split second it does not get a good ground ,that is why it is good to have that ground cable attached to the table to protect yourself from becoming the ground."

                                The above statement is untrue.

                                If it was true then anytime you change welding rods you would complete the circuit because you are standing on the ground & touching the stinger.

                                Having a pc. of wire going from your table leg to a ground rod or the ground in your panel will not complete the welding circuit. This is why when you forget to hook up your work cable nothing happens because it cannot complete the circuit.
                                Last edited by MMW; 02-16-2011, 05:39 PM.
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