Equpotential bonding

Discussion in 'Electrical Forum discussion & Blog' started by jwelectric, Mar 30, 2011.

  1. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Equipotential Plane as defined in Article 547 for Agricultural buildings An area where wire mesh or other conductive elements are embedded in or placed under concrete, bonded to all metal structures and fixed nonelectrical equipment that may become energized, and connected to the electrical grounding system to prevent a difference in voltage from developing within the plane.
    Equipotential Planes. The installation and bonding of equipotential planes shall comply with 547.10(A) and (B). For the purposes of this section, the term livestock shall not include poultry.
    (A) Where Required. Equipotential planes shall be installed where required in (A)(1) and (A)(2).
    (1) Indoors. Equipotential planes shall be installed in confinement areas with concrete floors where metallic equipment is located that may become energized and is accessible to livestock.
    (2) Outdoors. Equipotential planes shall be installed in concrete slabs where metallic equipment is located that may become energized and is accessible to livestock. The equipotential plane shall encompass the area where the livestock stands while accessing metallic equipment that may become energized.
    (B) Bonding. Equipotential planes shall be connected to the electrical grounding system. The bonding conductor shall be copper, insulated, covered or bare, and not smaller than 8 AWG. The means of bonding to wire mesh or conductive elements shall be by pressure connectors or clamps of brass, copper, copper alloy, or an equally substantial approved means. Slatted floors that are supported by structures that are a part of an equipotential plane shall not require bonding.

    Equipotential bonding as outlined in 680 for swimming pools
    680.26 Equipotential Bonding. (A) Performance. The equipotential bonding required by this section shall be installed to reduce voltage gradients in the pool area.
    (B) Bonded Parts. The parts specified in 680.26(B)(1) through (B)(7) shall be bonded together using solid copper conductors, insulated covered, or bare, not smaller than 8 AWG or with rigid metal conduit of brass or other identified corrosion-resistant metal. Connections to bonded parts shall be made in accordance with 250.8. An 8 AWG or larger solid copper bonding conductor provided to reduce voltage gradients in the pool area shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes.
    (1) Conductive Pool Shells. Bonding to conductive pool shells shall be provided as specified in 680.26(B)(1)(a) or (B)(1)(b). Poured concrete, pneumatically applied or sprayed concrete, and concrete block with painted or plastered coatings shall all be considered conductive materials due to water permeability and porosity. Vinyl liners and fiberglass composite shells shall be considered to be nonconductive materials.
    (a) Structural Reinforcing Steel. Unencapsulated structural reinforcing steel shall be bonded together by steel tie wires or the equivalent. Where structural reinforcing steel is encapsulated in a nonconductive compound, a copper conductor grid shall be installed in accordance with 680.26(B)(1)(b).
    (b) Copper Conductor Grid. A copper conductor grid shall be provided and shall comply with (b)(1) through (b)(4).
    (1) Be constructed of minimum 8 AWG bare solid copper conductors bonded to each other at all points of crossing
    (2) Conform to the contour of the pool and the pool deck
    (3) Be arranged in a 300-mm (12-in.) by 300-mm (12-in.) network of conductors in a uniformly spaced perpendicular grid pattern with a tolerance of 100 mm (4 in.)
    (4) Be secured within or under the pool no more than 150 mm (6 in.) from the outer contour of the pool shell
    (2) Perimeter Surfaces. The perimeter surface shall extend for 1 m (3 ft) horizontally beyond the inside walls of the pool and shall include unpaved surfaces as well as poured concrete and other types of paving. Bonding to perimeter surfaces shall be provided as specified in 680.26(B)(2)(a) or (2)(b) and shall be attached to the pool reinforcing steel or copper conductor grid at a minimum of four (4) points uniformly spaced around the perimeter of the pool. For nonconductive pool shells, bonding at four points shall not be required.
    (a) Structural Reinforcing Steel. Structural reinforcing steel shall be bonded in accordance with 680.26(B)(1)(a).
    (b) Alternate Means. Where structural reinforcing steel is not available or is encapsulated in a nonconductive compound, a copper conductor(s) shall be utilized where the following requirements are met:
    (1) At least one minimum 8 AWG bare solid copper conductor shall be provided.
    (2) The conductors shall follow the contour of the perimeter surface.
    (3) Only listed splices shall be permitted.
    (4) The required conductor shall be 450 to 600 mm (18 to 24 in.) from the inside walls of the pool.
    (5) The required conductor shall be secured within or under the perimeter surface 100 mm to 150 mm (4 in. to 6 in.) below the subgrade.
    (3) Metallic Components. All metallic parts of the pool structure, including reinforcing metal not addressed in 680.26(B)(1)(a), shall be bonded. Where reinforcing steel is encapsulated with a nonconductive compound, the reinforcing steel shall not be required to be bonded.
    (4) Underwater Lighting. All metal forming shells and mounting brackets of no-niche luminaires shall be bonded.
    Exception: Listed low-voltage lighting systems with nonmetallic forming shells shall not require bonding.
    (5) Metal Fittings. All metal fittings within or attached to the pool structure shall be bonded. Isolated parts that are not over 100 mm (4 in.) in any dimension and do not penetrate into the pool structure more than 25 mm (1 in.) shall not require bonding.
    (6) Electrical Equipment. Metal parts of electrical equipment associated with the pool water circulating system, including pump motors and metal parts of equipment associated with pool covers, including electric motors, shall be bonded.
    Exception: Metal parts of listed equipment incorporating an approved system of double insulation shall not be bonded.
    (a) Double-Insulated Water Pump Motors. Where a double-insulated water pump motor is installed under the provisions of this rule, a solid 8 AWG copper conductor of sufficient length to make a bonding connection to a replacement motor shall be extended from the bonding grid to an accessible point in the vicinity of the pool pump motor. Where there is no connection between the swimming pool bonding grid and the equipment grounding system for the premises, this bonding conductor shall be connected to the equipment grounding conductor of the motor circuit.
    (b) Pool Water Heaters. For pool water heaters rated at more than 50 amperes and having specific instructions regarding bonding and grounding, only those parts designated to be bonded shall be bonded and only those parts designated to be grounded shall be grounded.
    (7) Metal Wiring Methods and Equipment. Metal sheathed cables and raceways, metal piping, and all fixed metal parts shall be bonded.
    Exception No. 1: Those separated from the pool by a permanent barrier shall not be required to be bonded.
    Exception No. 2: Those greater than 1.5 m (5 ft) horizontally of the inside walls of the pool shall not be required to be bonded.
    Exception No. 3: Those greater than 3.7 m (12 ft) measured vertically above the maximum water level of the pool, or as measured vertically above any observation stands, towers, or platforms, or any diving structures, shall not be required to be bonded.
    (C) Pool Water. An intentional bond of a minimum conductive surface area of 5806 mm2 (9 in.2) shall be installed in contact with the pool water. This bond shall be permitted to consist of parts that are required to be bonded in 680.26(B).

    Notice that in the main body of the text of 680.26(B) it clearly states that this grid is not required to be bonded to any type of grounding electrode. The purpose of this grid is to have the pool, the water, and the area for 3 feet out at the same potential.

    The equipotential plane for al and Artificially Made Bodies of Water as outlined in 682
    Equipotential Plane. An area where wire mesh or other conductive elements are on, embedded in, or placed under the walk surface within 75 mm (3 in.), bonded to all metal structures and fixed nonelectrical equipment that may become energized, and connected to the electrical grounding system to prevent a difference in voltage from developing within the plane.

    The only place the equipotential plane is required ;
    682.33 Equipotential Planes and Bonding of Equipotential Planes. An equipotential plane shall be installed where required in this section to mitigate step and touch voltages at electrical equipment.
    (A) Areas Requiring Equipotential Planes. Equipotential planes shall be installed adjacent to all outdoor service equipment or disconnecting means that control equipment in or on water, that have a metallic enclosure and controls accessible to personnel, and that are likely to become energized. The equipotential plane shall encompass the area around the equipment and shall extend from the area directly below the equipment out not less than 900 mm (36 in.) in all directions from which a person would be able to stand and come in contact with the equipment.

    None of these equipotential planes are required to have any type of ground rod installed. The purpose of each of these equipotential bonding is to make everything at the same potential and not to connect it to earth to let current bleed of into the earth.
    The laws of electrical current physics mandate that the electrons that leave a power source must return to that source and cannot be bled of to anything.
  2. Randyj

    Randyj Master Plumber

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    If you put all that metal in the earth, mesh, etc... then it mitigates any need for a ground rod. It would pretty much be duplicating the same principle/idea. No need to kill the same cow twice. :O)
  3. jwelectric

    jwelectric Electrical Contractor/Instructor

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    A ground rod will not do the same thing that the grid will do. The rod covers the area the same as the area of the rod but 8 feet deep. The grid covers the entire area and makes the entire area at the same potential.

    What neither does is remove the stray voltages.

    Take a voltage reading on a single pole light switch with the switch off. You should have a reading from one screw to the other screw of 120 volts. Turn the switch on and the voltage reading goes away. Now you have the same potential across the screw that is not giving you a voltage reading but the light is burning. Did we remove the voltage? Is the voltage somehow leaking somewhere? No the two screws are at the same potential and from either screw to the equipment grounding conductor will be 120 volts.

    DON’T TRY THIS!!!!!!!!!!!!!!!! If I was standing on a rubber mat and not touching anything with the switch on I could touch both screws at the same time and feel nothing even though the light was burning but the second that I turned the switch off it would jar my teeth and I would jump back from the pain. It is called being at the same potential no shock an being across a potential of 120 volts feeling the current.

    No more than the voltage was removed from the screws can the installation of ground rods or a grid remove the voltages from earth, it simply brings the exposed surfaces to the same potential as earth just as the repair man on the power line in the link I posted in the other thread.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    When working on a high-powered radar, the filaments often only need 5vdc or so, but the rest of the thing might be running at 40K v. Now, if these were isolated, at 40K volts, it would arc to the filaments and run to ground (return) that way, since it would be a lower resistance path. So, they run the filaments at 40,005 volts, with its own return. You need to be VERY careful how you measure this, but in this case the filaments only have 5vdc on them, even though if you measured to ground, you'd get 40,005!

    There are numerous things that can go on in any wiring situation, and having properly designed current paths and grounds is critical to safety and proper operation. The NEC has been around for a long time, and they've worked out the kinks. Trying to second guess them is just asking for problems. Yes, there are changes made over the years, but those are because someone often discovers one of those 'what if' situations, that hadn't been thought of previously, or newer materials came into play that changed how things should be installed to maintain safety.

    While it is satisfying to understand the rules, it is not absolutely necessary to provide a safe environment, as long as you follow the rules, you've made it. Understanding, grasshopper, often takes time and practice!
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

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    well put and thank you
  6. DonL

    DonL Jack of all trades

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    Hello Group,

    If this is true;
    "they run the filaments at 40,005 volts"

    Then How do you regulate the Voltage for the filament of the RF tube to 40,005 V ?

    Normally the filament transformer is isolated so that the Tube will not ARC and puts out 5 to 6 volts, depending on the type of RF Tube.

    Putting 40,005 V on a filament would not work to make up the 5 Volt filament difference , Because regulating a 40,000 V power source to .000125 % is nearly imposable. ( If you have a design, I want it and you should patten it, It would be worth big bucks)

    It may have 40,000 V on it but most RF tubes want to be operated within .5 Volts of there operating filament Voltage, and they are
    isolated and put only the voltage that the filament needs..

    Something is wrong with the picture you are drawing. No need to confuse people, Who want to learn something.

    I have some good Volt-meters, but expecting one to measure the difference of 40,000 - 40,005 just is not going to happen,
    It the real world.

    DonL.

    "Theory only works in a vacuum" , there are just to many unknown variables in every day life.

    PS. Jim I understand what You mean, but when there is a Instructor in the room You need to be correct.
    I am glad I was not in his class, I would have gotten an F, LOL.
    Last edited: Apr 12, 2011
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Don, have you ever worked on an actual radar? The filament supply is floating at the high side of the high voltage so it has the same reference point, and is truely 5vdc across the filaments, where across the body of the tube, its 40000, just that instead of measuring from ground, you're measuring from the 40000 level. this way, the filaments don't arc to the body since they're only 5vdc different. When testing, yes, you can measure the 5vdc...you leave the HV off and use the same reference point. It would get too messy and hard to accurately measure 40005 verses 40000 without arcing stuff, and probably ruining things in the process. But, you can measure the 40K separately, and with that off, the 5v easily.
  8. Randyj

    Randyj Master Plumber

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    This can be a bit confusing as a voltage reading is not reading a voltage potential but it is a reading of difference in potential... or saying it another way, the difference in the flow of electrons. So, the reading alone is misleading... if you got a voltage reading of zero then for all we know the potential on those screws could be a gazillion volts from another point of reference.
  9. nukeman

    nukeman Nuclear Engineer

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    Voltage is always some potential to some reference point. Typically, ground/chassis of equipment is used as the reference point and everything else can be higher/lower.

    You can think of it like gravity potential. Do you measue the hill from the top to the bottom? Do you referenece both points to sea level? How about reference to the highest point on Earth? All values are quite different, but the potential (top of the hill to the bottom) will be the same no matter which reference point you choose.

    In terms of getting a shock, it is all about the potential across your body. You can stand in a metal cage and charge it to 1,000,000 V, and you won't feel a thing since there is no potential across your body. Not the case for someone touching the cage from the outside though!
  10. Randyj

    Randyj Master Plumber

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    well... yeah, uh huh, yes, no... it ain't the same as a linear measurement. Ya gotta have electrons moving through a point to be able to count'em.. .of course, voltage is thought of as "pressure" whereas current is a value of the number of electrons moving past a specific place in a specific amount of time.
    ... and uh... my physics classes ended when we started touching on quantum physics and I'm totally lost there...
  11. DonL

    DonL Jack of all trades

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    AMEM nukeman...
  12. nukeman

    nukeman Nuclear Engineer

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    Sure, it's linear. You don't need electrons moving to have a voltage. Just like you don't need to be falling to have potential when hanging off the side of a 100-storey building. Same difference.

    For instance, you can have the main breaker off at your house (no current, no electrons moving), but you know there is still 240v feeding it.
  13. Randyj

    Randyj Master Plumber

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    Well Nukie... that's a very good comparison.... Thanks!
  14. DonL

    DonL Jack of all trades

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    Good Morning Group,

    "Don, have you ever worked on an actual radar?"

    Yes Jim I have worked with Radar Transmitters, and the way the magnetron gets its filament voltage is the same way a Microwave Oven
    magnetron tube operates.

    The theory of operation is the same, except the Microwave oven operates at 2450 MHZ so that it reacts with water molecules,
    and the Radar transmitter frequency is normally much higher, and is normally pulsed AM modulation and Microwave ovens are CW.

    Have a Great Day.

    DonL
  15. ballvalve

    ballvalve General Engineering Contractor

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    Why / who started the [residential, at least] deal with trying to wrap 10 or 12 feet of rod into the earth, usually impossible - usually cut off and banged up again-?

    Most every pole has a trench at it - why not start laying grids or rods horizontally as the norm?
  16. DonL

    DonL Jack of all trades

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    That is a Very Good question BallValve.

    Where I live you hit water at 10-12 feet, When we have rain.

    I install all my own ground systems, because I live in the country and they don't even maintain there PolePigs. (Transformers are Rusty and leak oil)

    My tower Takes Lightning strikes on a normal basis, and I have yet to have a problem with the electronics connected to it.

    Now that every thing is put in underground with PVC, You can not even rely on it for a ground.

    Have a Great Day.

    DonL
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

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    With a rod the deeper the better.
    In most areas across America using a 8 foot rod will have around 300 ohms but to extend this rod to 30 or more feet will drop the resistance to 30 ohms or less.

    To lay one flat 30 inches deep is a waste of time
  18. DonL

    DonL Jack of all trades

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    Hello jwelectric and the Group,

    JW what do you think about using salt for increasing Ground Conductivity ?

    DonL
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Two questions

    What do you think the salt will do to the rod?

    How long do you think the salt will last before it is gone?

    I think it is a waste of time and money
  20. DonL

    DonL Jack of all trades

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    Hello jw and the group.

    It depends what type of rod that You use, as to what salt or what ever chemical you use to make the system
    work at 5 ohms or less. 5 ohms is a good target, for a good system.

    You posted "In most areas across America using a 8 foot rod will have around 300 ohms"

    That would mean that homes in the U.S.A. are not meeting the standard, 8 foot rods are the requirement for Texas.

    300 ohms ? it that resistance or impedance ? I assume if it is impedance then You are measuring at 60 HZ.
    300 ohms don't get it, Not in any spec that I have heard of, for grounding. Correct me if I am wrong.

    And of course you would have to replenish the salt as it gets absorbed, into the earth.

    You say "I think it is a waste of time and money" , Then many engineers are wasting time and money, for a proven method that works. But they shoot for 5 ohms or less. unless they are in desert sand. It does work, proven.

    I just want to make sure I understand what You are talking about, and teaching.

    I am old school and nothing has changed since the invention of the light bulb, except they outlaw the production of incandescent bulbs in the U.S.A. (No more easy bake ovens, or light bulbs in your oven or fridge) As far as electron theory goes, Still works the same.

    You will rarely see 12 8 foot rods at one location, Just to meet the 25 Ohm norm.

    I just want to be on the same page as You, What page are You on ?

    Have a Great Day.

    DonL
    Last edited: Apr 15, 2011
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