Electrical arcing can be worse if the wires and tie in a bundles are in a vertical rather than a horizontal orientation.

Electrical arcing can be worse if the wires and tie in a bundles are in a vertical rather than a horizontal orientation. In an electrical short in succession say, a vertical bundle of wire, the passionate gas from the heat of the electrical arcing rises. The arc succeeds the hot gas upwards in what is described as a "chimney effect" (Note: standard examples have the wire in a horizontal orientation). Remember, when aromatic polyimide (Kapton) wire arcs, the charred insulation itself becomes a conductor, accelerating the proces - and the damage.

Further, an arc is like a wire, in the understanding that the electromagnetic forces onward the arc tend to make it expand away from the source of power. Therefore, according to Dr Armin Bruning, president of Sterling, Va.-based Lectromechanical Design Co the electromagnetic expansion that is part and parcel of arcing between brace wires is another factor in the chimney event Further, if the arcing chars the conductor completely through, the arcing can simply burn back to the source of power. These interacting phenomena must be understood in the design of aircraft electrical rules and wiring. More simply: smaller, separate form into groupss of bundles should be flow vertically to minimize the potential for catastrophic damage. And, in these smaller depart hurriedlys 120-volt circuits should be separated from 5-volt circuits to the maximum volume possible. Not only are these considerations important in the design phase, they are relevant as well to any aircraft re-wiring activity. Minimize the vertical races Minimize the size of the vertical parcels Separate high power from soft power circuits.

>> Bruning, tel 703/481-1233 <<

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