Aarding: Maximum tolerable body currents and voltages

Do you want to become an expert on the topic of electrical safety? This online course teaches about the risk of ventricular fibrillation (VF) as a result of body currents. The risk depends on the current magnitude, current path, duration and time of occurrence. Studies have been performed by different persons over time. This elearning explains the history and establishment in IEEE Std.80 and IEC.

Then, background information of the body impedance will be provided. The body impedance is the sum of the internal impedance of the human body and the impedance of the skin. They depend on current path, touch voltage, duration of current flow, frequency, degree of moisture of the skin, surface area, pressure exerted and temperature.

Finally, there are different types of additional resistances that may be applied during the investigation of the tolerable (touch) safety of a potentially hazardous situation. In the end, the total electrical chain can be investigated.

Tools

Five excel tools will become available; two tools containing the curves from IEEE and IEC that describe the relationship between the maximum tolerable body current and the duration of a shock. The first tool contains the classic curves, determined using different methods (read from the graph, and described by formula’s), the second also contains new proposed (but not yet accepted) curves.

The third tool describes the body impedance as provided by IEC 60479-1. The fourth tool describes additional resistances as a result of surface treatment (using asphalt or gravel). The fifth tool combines all four together and provides you with calculated values, giving you the choice to select different methods and input criteria.

Prerequisites for the use of the tools: a recent version of MS Office Excel shall be used with the option to run VBA macro’s. You will need to run these tools to complete the course. If the user wants to extend or change the tool experience with Excel and VBA will be necessary.

Other

References: this module mainly refers to IEEE Std 80 and IEC 60479-1.

Key words: earthing; grounding step and touch potentials; electrical safety; maximum tolerable body current; additional resistance; shoe resistance; duration; short circuit current;

Trefwoorden: aarding; stap en aanraakspanningen; elektrische veiligheid; maximaal toelaatbare lichaamsstroom; additionele weerstand; shoeiselweerstand; duur; kortsluitstroom