On 6 April 2018 at 10:57, Bob Blick wrote: > I was thinking about how wires in DC spot welders jump when you perform a > weld, and how it's most likely electromagnetic forces. Then it got me > thinking about how it affects power transmission with long spans between > the towers. Those wires are far enough apart and other losses are dominan= t, > so I'm sure it's insignificant. > Telephone exchange busbars suck [tm]. Removing some of the spacers during maintenance turned out to be a VERY bad idea in at least one case I read of. Operating currents can be in the thousands of Amps at 50V. Short cct current is "higher. Back then, SC protection was fuses. Accidentally (presumably) shorting a metal vacuum cleaner tube across the busbars and dropping a wrench thereon was also reported to have been a bad idea. Once started an arc would probably have no problem maintaining, and welded bits of the starter metal would probably help. I once did not have the nerve to turn off the contactors in a 230V/400V commercial switchboard in a cafe I was eating at when the switchboard started throwing impressive arcs from place to place on the FRONT of the board. I don't know how it managed that and did not wish to become part of its show. Friends had phase and neutral to their home swapped by an electrician !!!. On re-enabling steam came out of the cold taps, the house groaned and moaned and worms crawled out of the ground. Really. The electrician had left before the effects became noticed so they had to summon help. Alas I only heard of it latterly. Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .