Grounding Techniques for ESD Flooring
To achieve the electrical specifications for the static control (esd) flooring materials you have selected your floor must be properly grounded. Proper grounding runs the full gamut from simple to technically challenging. Static control floor grounding techniques are important in even the most basic of environments and critical in protected electronic manufacturing environments, explosive, ordinance and munitions environments. At United ESD we are specialist in grounding your static control floor to a multitude of requirements from basic to advanced to critical When contracting requirements dictate (as in the case of FAA and Ordinance installations) we work exclusively with Ahrens Construction of Nevada to provide full building grounding, full perimeter grounding and equiplane full copper sheeting underlayments beneath our esd floors. Ahrens construction specializes in working with the FAA, 911 and Command Centers and the Military providing quality, reliability and the advanced expertise so necessary when conditions call for the most stringent, CRITICAL requirements. Although grounding your esd floor is imperative, most installations now dictate a relatively basic grounding method due to recent advancements inherent in the new higher conductivity adhesives. This basic method is now generally adequate in achieving an installed electrical RTG (resistance to ground) close to the center of the flooring systems electrical conductivity range. We generally supply (at no charge with your flooring order) a quantity of grounding hardware appropriate for basic grounding in non-critical standard environments. The quantity of grounding hardware we provide is for use with installations utilizing one of our conductive adhesive to concrete substrates. All of our ESD flooring materials are designed to work in conjunction with our permanent one part, water based acrylic liquid conductive adhesive (US C 2000), our unique releasable adhesive "Tape" (URAS), or our NEW US C2004 R Liquid conductive releasable adhesive. All adhesives provide reliable anchoring of the flooring, as well as a equiplane of fairly high, permanent conductivity (typical between 1.0E02 and 1.0E04) allowing equalization of electrostatic potential for subsequent elimination via ground straps placed into the adhesive and beneath the esd floors. Your goal when grounding any esd floor is to provide a reliable, long lasting mechanical connection from your ESD flooring and adhesive to a dependable earthed electrical ground in your building and to come as close as possible to the lower middle of the materials specified resistance to electrical ground. BASIC GROUNDING OF AN ESD FLOOR A variety substrates may be covered with esd flooring. Non conductive (insulative) substrates will somewhat affect the conductivity of certain flooring, more so with static dissipative materials like ElectraFloor "Fundamentals" (that rely mostly on the ambient humidity in your environment for conductivity) than conductive flooring like our UltraStatic ESD control Tiles (that are non humidity dependant). When covering wood, standard VCT or epoxy substrates additional grounding straps may be required. It's always best to "check RTG as you go" when encountering highly insulative surfaces and adjust the number of flooring grounds accordingly. Conversely, concrete surfaces, devoid of sealers and finishes are inherently conductive. Although concrete's conductivity will fluctuate dramatically (depending on the ambient humidity of your environment and the moisture content of the concrete) it will always have areas of conductivity, helping to make grounding of your esd floor relatively easy. Our experience has shown that with the static conductive or dissipative non-humidity dependant esd vinyl's and carpeting, covering a cement substrate, only one ground per 1000 SF is normally required. When covering insulative substrates or when working with humidity dependant esd floor covering materials 1 ground per 500 SF will provide the best results. Method 1) One of the most popular methods of grounding is to locate an AC electrical outlet, turn off the power to the outlet, place 12" of our 2" heavy duty copper foil into the wet adhesive (directly beneath the outlet), place conductive adhesive over the pre-placed strip (for subsequent covering with the esd flooring). Extend the remaining 12" up the wall (double sided tape or a dab of adhesive placed on the back of the strip can help hold the strip securely to the wall). Carefully remove the face plate cover of the outlet and loosen the bottom of the electrical plug from its wall retainer. Most electrical outlets have 2 small "ears" at the bottom of the outlet that facilitate as a flush mounting stop. Carefully remove the center screw (between the ears) and run a section of the copper strap behind the ears (trim as required). Replace the screw, going through the copper foil and pulling the outlet back flush with the wall. Replace the face plate cover and test strap for electrical resistance to ground. For esd floor grounding purposes a reading below 1 ohm resistance to electrical ground is sufficient. Method 2) Another popular method of grounding an esd floor utilizes the same quantity and type of esd copper foil. In method 2 the foil may be terminated where convenient. With approximately 8" of the copper foil placed into the wet adhesive and 8" running up the wall to a heavy gauge copper grounding bus terminated to the building AC electrical ground via electrician installed cabling. Method 3) Useful on large floors or floors where an ac outlet or grounding bus is not available relies on the use of steel columns, water pipes and other permanently grounded structural items for grounding terminations. First, check the electrical resistance of the item, clean connection point as needed to achieve <1ohm between item and AC electrical ground. Permanently attach copper strip (see drawing 2).
Figure 1
1: conductive adhesive,
prior to covering with esd flooring
Figure 2 In this sketch a steel column (1) is used as (2) an attachment point for the copper strap subsequently placed in (3) wet conductive adhesive prior to covering with (4) esd flooring.
INSTALLATION AND USAGE OF COPPER OR SILVER GROUND GRID In some situations a copper foil ground grid is installed on the substrate prior to application of the conductive adhesive. Our .500 wide by .002 thick, adhesive backed (liner covered) esd grounding foil works great for this application (if required by your internal specifications). This is a common procedure for FAA control towers and the Military. This procedure is often used in conjunction with the 2" wide copper strip as a termination utilizing the same attachment of the pigtail as outlined above. Note: with the use of the new higher conductivity adhesives and advancements in the manufacturing of esd flooring this method generally will neither increase nor decrease the electrical consistency or conductivity of your flooring's resistance to ground.
Our conductive adhesive backed grounding foil is supplied in roll form and is convenient for pre-placing any required grounding grid beneath your ESD flooring material. The foil is subsequently attached to multiple permanently grounded objects (such as those listed above). To apply, sweep or vacuum substrate to remove loose dust and debris. Remove the adhesive liner (backing) from the Foil and press firmly in place on substrate. Gently pull tape as you unroll (to keep from puckering), smooth the tape in place with foot or towel. The tape may be attached to ground by simply (with liner removed), running the tape up (or on) the permanently grounded object, however this will typically not meet our <1ohm RTG as the tapes adhesive is not conductive. Better results may be obtained by placing a 2" wide copper foil strap over convenient sections of the adhesive covered grid and attaching as shown in methods 1,2 or 3. To achieve ultimate contact between the grid overlayment center punch as shown. Test the grid for electrical resistance to ground making sure to achieve < 1 W AC Impedance from any given point.
Large floor, < 2 W AC Impedance
Center punch
GROUNDING FAA AND CANADIAN FORCES AIR TRAFFIC CONTROL TOWERS
Air Traffic control towers present many variables in grounding and covering. This photo shows a plywood substrate primed with latex and "floated" with a sanded, cementious underlayment and subsequent placement of grounded foil grid.
Air traffic control towers generally have a combination of flooring substrates that must carefully be taken into consideration when grounding and covering with esd flooring. The majority of the substrate will typically be plywood with smaller access panels made from steel. In most cases (especially older towers) height differences, protruding and loose nails and excessively worn wood substrates will necessitate the use of a latex primer and subsequent application of a cementious underlayment prior to grounding. The use of these underlayments and the fact that the majority of the substrate is highly insulative and highly conductive can present unusual variances in final resistance to ground measurements of the applied flooring. To help alleviate potential "hot and cold" electrical resistance readings in your finished floor we recommend the placement of a copper foil grid (center punched at intersecting grid points) and tested after attachment to approved grounding terminations, (typically the multipoint equipment ground). This grid should post < 1 W AC Impedance to said grounding terminal at any point tested WORK IN PROGRESS EQUIPLANE GROUNDING
equiplane grounding
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