Eliminate Shunt Maintenance with the World's First Retractable Grounding Assembly for Tank Protection

An innovative product that facilitates grounding of floating roof tanks is described by its manufacturer.

Lightning Eliminators and Consultants (LEC), of Boulder Colorado have developed a retractable grounding assembly for large aboveground floating roof tanks. The new device, dubbed the Retractable Grounding Assembly (RGA™), reduces the bound charge hazard by equalizing the floating roof and tank wall potential, reducing any secondary arc hazard, which can ignite fires or explosions in flammable liquid storage tanks. Bound charge can be 1,000 times more common than direct lightning strikes, with impedance of just one ohm or less. Other grounding methods, such as shunts, wipers, or walkways may have impedance of over 500 ohms.

Bound charge occurs when a storm cell induces an electrical charge on everything beneath it, including metal containers and the flammable product within them. Secondary arc, leading to rim fires or explosions, results when the electrical charge differential between a tank wall and its floating roof, rises to the point where the charge can bridge the small air gap between the structures before it can be equalized. A nearby lightning strike, or even filling or emptying a tank quickly, can cause this to occur.

The manufacturer, LEC, claims that traditional methods for grounding floating roofs fall short of full effectiveness. Shunts bend or disconnect when a floating roof drifts off center, requiring frequent maintenance, and a build up of rust or paint tend to insulate shunts, walkways and grounding contacts from tank walls. The RGA method avoids these problems by employing a direct connection from the tank roof to the tank wall through a wide, thick-braided wire, wound on a reel for maximum conductivity. Retractable 480/30 copper wire aligns vertically beneath either a top edge
or angle mount, and attaches to the floating roof, serving as a highly efficient grounding conductor.

Because secondary arcing can occur in as little as 20 milliseconds, fast efficient conductivity is critical in preventing it. Unlike traditional methods, LEC uses a wide braid to maximize surface area and therefore conductivity, since electrical charges travel most effectively along the surface of a wire. In addition, a spring-loaded reel extends the grounding wire as the roof descends, and retracts it as the roof rises; the line remains taut at the minimal distance needed for grounding. Less wiring translates into less conductive resistance and faster, more reliable grounding.

RGA system includes a stainless steel reel assemblies, eliminate the risk of bound charge and secondary arc in floating roof storage tanks and are claimed to require little maintenance. A single RGA is effective for tanks with diameters of up to 30 meters, with more recommended for tanks of larger size.

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