Visit the Machine Building Systems web site

Retractable grounding reduces bound charge risks

A Lightning Eliminators and Consultants product story

Edited by the Engineeringtalk editorial team Jul 1, 2005

Lightning Eliminators and Consultants (LEC) is announcing what is claimed to be the world's first Retractable Grounding Assembly (RGATM) for liquid storage tanks with floating roofs.

Lightning Eliminators and Consultants (LEC), a leader in preventive and protective lightning technology, is announcing what is claimed to be the world's first Retractable Grounding Assembly (RGATM) for liquid storage tanks with floating roofs.

The new device reduces the bound charge hazard by equalising 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 1000 times more common than direct lightning strikes.

With impedance of just one ohm or less - compared to shunts, wipers, or walkways with impedance of over 500 ohms - the RGA ensures a reliable, full-time grounding connection.

Bound charge occurs when a storm cell induces an electrical charge on everything beneath it, including metal containers and the flammable products 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 equalised.

A nearby lightning strike, or even filling or emptying a tank quickly, can cause this to occur.

"Traditional grounding methods have fallen short," says Jerry Kerr, LEC's marketing director.

"Shunts bend or disconnect when a floating roof drifts off-centre, requiring frequent maintenance.

"Factors such as the build up of rust, paint, or other contact degradation tend to insulate shunts, walkways and grounding contacts from tank walls.

"LEC's RGA, however, is 100 per cent effective - without relying on shunts or questionable grounding contacts.

"It's simply the most effective floating roof grounding system on the market today, with a return on investment (ROI) of less than 16 months".

Providing a direct connection from the tank roof to the tank wall, the RGA uses 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 an ever ready, 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, the RGA's wide braid maximises surface area and therefore conductivity, since electrical charges travel most effectively along the surface of a wire.

In addition, a spring-loaded reel extends wiring as the roof descends, and retracts it as the roof rises - so the line remains taut at the minimal distance needed for grounding.

Less wiring translates into less conductive resistance and faster, more reliable grounding.

RGAs, with stainless steel reel assemblies, eliminate the risk of bound charge and secondary arc in all floating roof storage tanks and require almost no maintenance.

A single RGA is effective for tanks with diameters of up to 30m, with more recommended for tanks of larger size.

Lightning Eliminators and Consultants designs, manufactures, and installs integrated, engineered systems to prevent and eliminate lightning related problems.

For more information about the new retractable grounding assembly, contact the company now or visit the website.