The calculation of current ratings for groups of (multiple) cable circuits require the quantification of the mutual heating component between the groups of circuits. This example is for multiple groups of circuits in air on the same cable ladder. This article will discuss the IEC 60287 approach.
The effects of lightning strikes on earthing or protection systems designed to IEC 62305 can be modelled using an equivalent single frequency from 25kHz up to 1MHz which gives similar results to a time-domain approach. This article provides the frequency and current values to be used for modelling lightning.
This report shows the effects of a direct lightning strike to an air terminal installed on top of a building which is connected to a buried earthing system.
This report shows the effects of soil resistivity and thickness of layers on grid resistance for earthing systems in multilayer soils. Increasing the resistivity of soil layers tends to increase the grid resistance, no matter which soil layer that is. Increasing the thickness of any soil layer with high resistivity also increases grid resistance and if the soil layer thickness is increased for a low resistivity layer then the grid resistance will decrease.
Electrical equipment operating at or above 50 V AC or 120 V DC which will not put into a deenergised state during work must be evaluated for arc flash and shock protection. Three types of activities of workers carry the highest risk of arc flash. Three main factors determine the severity of an arc flash injury.
Earthing rods improve earthing systems when driven into low resistivity soil layers. Due to the proximity effect the rule of thumb is earth rods should be separated by at least their driven length. Rods may be encased in concrete to lower their resistance. Equations are provided for hand calculations and these have been validated with numerical software.