On Sun, 08 Feb 2015 13:28:17 -0800, jim wrote: > >( ... ) > > Modern American electrical code requires a >big-sized bare conductor (and some minimum >length requirement that I forget) coiled into any >poured concrete foundation. This is an effective >ground. > Simply drilling into concrete and installing some >conductive rod is ineffective. > Some practitioners use multiple ground rods, >all connected together, driven into the earth, with >a big conductor from the ground rod array to the >service entrance. There are different sizes of >grounding rod, from 1/2 inch to 1 inc diameter. > > Most of us have no control over the electrical >wiring we use. > With rare exceptions, initial electrical wiring is >proper. Problems show up after non-electricians >(handy personages, cheap M. Mouse laborers...) >show up to extend or repair things. It's hard to >wire things badly because the suppliers sell only >devices that conform to the National Electrical >Code--wiring things up is a matter of using the >right tinker toy, hard to get wrong other than >swapping the neutral and the hot (hot is either >red or black and connects to a brass colored >screw; neutral is white and connects to a silver >colored screw; ground wires are either green >or bare copper and connect to a green colored >screw). > > If you own your own home and it uses a >grounding rod, consider sinking another one or >two or five or 27 and connecting them all together. > Multiple grounding rods reduce the impedance >of the barrier between a single grounding rod and >the actual dirt into which it's sunk by a factor of >the number of grounding rods (two rods halve >the impedance between the service ground lug >and true earth). > Note that the size of the conductor should be >huge (#4 at minimum, 0 or 00 or greater can't >hurt and might be correct depending on expected >ampacity). This conductor must connect each of >the ground rods to the others as well as (a single >length) to the service entrance bonding lug. > Note also that the devices that clamp the wire >to the grounding rods must be the correct size >and material for both the rod and for the wire. > If you have grounding problems, it's likely that >the original grounding components have >corroded or become loose. Either presents a >potentially dangerous shock hazard. (Adding >grounding rods to a working system does not >as long as you do not break the existing >connections.) You might have noticed that my English isn't that good, perhaps somebody is able to translate what the German Wiki says. It would be much better to translate the DIN VDE. All in all there are issues, such as interaction of ground systems. So there's no security. In fact you should ask your local electricity provider to do measurements from time to time, but nobody does, since it's not for free. What's working today could be damaged next week. The DIY market tool to check ground is not good enough. Potential equalisation minimizes potential difference, but the potential difference might not be zero. Time for a real time-out. But I guess this topic was too important to not breathe a word. Regards, Ralf http://de.wikipedia.org/wiki/Potentialausgleich "Potentialausgleich bezeichnet eine elektrisch gut leitfähige Verbindung, die unterschiedliche elektrische Potentiale minimiert." http://de.wikipedia.org/wiki/Erdung "Nur in statischen Anwendungsfällen darf daher davon ausgegangen werden, dass mit der Erdung jegliche Potentialdifferenz ausgeschlossen ist." "Aufgrund der Vielzahl von unterschiedlichen Erdungssystemen kann es zu Beeinflussung der Erdungssysteme untereinander kommen. Dieses macht sich besonders in städtischen Gebieten mit dichter Bebauung bemerkbar, wenn Bahntrassen in der Nähe der Bebauung verlaufen. Durch Potentialverschleppungen kann es zu Überlagerungen des Bahnstromes auf das Drehstromnetz kommen. Dies führt dazu, dass Anlagen nicht mehr einwandfrei funktionieren. Im schlimmsten Fall können diese Überlagerungen zu Schäden am Erder führen oder sogar den PEN-Leiter zerstören. Durch vagabundierende Gleichströme kommt es in der Nähe von Gleichstrombahnen zu starken Korrosionen an Erdern aus feuerverzinktem Stahl. Über die Erdung ins Erdreich eingeleitete Wechselströme führen über längere Zeit zu Korrosionen an Rohrleitungen. Dies wirkt sich dann besonders aus wenn Rohrleitungen als Erder genutzt werden. Prüfung Das Vorhandensein eines Anschlusses zu einem Potentialerder allein bietet noch keine Gewähr für dessen Tauglichkeit und eine sichere Erdung. Daher muss nach dem Einrichten eines Potentialerders eine Prüfung auf Ableitung von Fehlerströmen nach VDE 0100 usw. erfolgen." _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
