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Standby letter of credit (SBLC): Operates like a commercial letter of credit, except that typically it is retained as a standby instead of being the intended payment mechanism. In other words, this is an LC which is intended to provide a source of payment in the event of non-performance of contract.
A grounded wire is sometimes strung along the tops of the towers to provide lightning protection. An optical ground wire is a more advanced version with embedded optical fibers for communication. Overhead wire markers can be mounted on the ground wire to meet International Civil Aviation Organization recommendations. [7]
NEC 2008 400.22(f) allows surface marking with ridged, grooves or white stripes on the surface of lamp cord. With transparent cord the hot wire is copper colored, and the neutral is silver colored. Grounding wire of circuit may be bare or identified insulated wire of green or green having yellow stripes. All metallic systems in a building are ...
An OPGW cable was patented by BICC in 1977 [1] and installation of optical ground wires became widespread starting in the 1980s. In the peak year of 2000, around 60,000 km of OPGW was installed worldwide. Asia, especially China, has become the largest regional market for OPGW used in transmission-line construction. [3]
Some examples of skin depth in copper wire at different frequencies are: At 60 Hz, the skin depth of a copper wire is about 7.6 mm (0.30 inches). At 60,000 Hz (60 kHz), the skin depth of copper wire is about 0.25 mm (0.0098 inches). At 6,000,000 Hz (6 MHz), [5] the skin depth of copper wire is about 25 μm (0.00098 inches).
To reduce this loss these antennas often use a conductive copper ground screen under the antenna connected to the buried ground wires, either lying on the ground or elevated a few feet, to shield the ground from the electric field. In a few cases where rocky or sandy soil has too high a resistance for a buried ground, a counterpoise is used. [11]
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Power cables use stranded copper or aluminum conductors, although small power cables may use solid conductors in sizes of up to 1/0. (For a detailed discussion on copper cables, see: Copper wire and cable.). The cable may include uninsulated conductors used for the circuit neutral or for ground (earth) connection.