Letter Re: Steel Buildings

HJL,

The writer of this letter has a few things wrong with regards the electrical properties of materials.

  1. Dielectric is a property of insulators, and there is no insulator between the zinc coating and the steel base of galvanized steel. Therefore, all the resulting claims that assume that the zinc and steel form a capacitor are false.
  2. The biggest problem with the shell of a metal building acting as a Faraday cage is the gaps between the panels that make up the surface. To act correctly as a Faraday cage the conductive surfaces need to make good electrical connection between the panels along all the seams. Ordinary construction techniques can’t be counted on to provide good electrical connection between the panels at the seams.

    Copper mesh can be used to make a good Faraday cage because copper can be soldered to, and the seams can be soldered or welded to provide reliable electrical connection between the panels.

    Trying to rely on mechanical connection instead of soldering or welding between panels may work as first but with time will degrade as the overlapped joints corrode.

  3. Concrete is slightly conductive, and concrete in contact with the earth such as a foundation or slab on grade with conductive materials embedded in it (think rebar) makes an excellent ground. Embed copper mesh in a concrete floor that is poured on grade, and the copper will be effectively grounded through the concrete. Bringing the mesh up above the concrete around the perimeter of the floor is important to allow it to be coupled without gaps to the conductive walls (and ceiling) that make up the rest of the Faraday cage.
  4. Grounding a Faraday cage never hurts, but is totally unnecessary for the functioning of the Faraday cage. The reason we ground electrical service entrances to buildings is to divert lightning strikes to the power lines to earth ground and greatly reduce the chances of lightning induced building fires. – RR
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