On 12/10/2015 11:06 AM, Gene Heskett wrote: > On Thursday 10 December 2015 10:16:40 Dave Cole wrote: > >> On 12/10/2015 4:06 AM, Gene Heskett wrote: >>> On Wednesday 09 December 2015 23:30:15 Todd Zuercher wrote: >>>> Is there a way to issue a stop/start command to the sserial >>>> interface on the 5i25? >>>> >>>> I am a little bit at a loss where to begin with looking for the >>>> source of the possible noise issue. Peter mentioned earlier some >>>> things to check. The DB25 cable is the one that came with the Mesa >>>> plug and go kit, and is not routed near any power cables, The >>>> power source for the servo drives is 220 3 phase and the PC is on >>>> 110 single phase, arranging for them to use the same power source >>>> may be difficult. >>> Todd, if the power company didn't use a wild leg (and I haven't >>> seen one of those since back in the '50's of the last century) for >>> the "220" 3 phase, but a true 3 phase circuit using a transformer >>> per phase at the service pole, which today on this side of the pond >>> is 254 volts per phase, measured from phase to phase. The trick is >>> to treat the "220" load as a delta load, where the 4th wire neutral >>> is just for equipment grounding. But, measuring that same set of 3 >>> wires from each wire to the neutral, looking at it as a "wye" load >>> should show nominally 127 volts to neutral for all 3 wires. The >>> critical measurement, to detect whether the power company used a >>> wild leg, is to measure from each of those 3 hot wires, to a local >>> ground rod. If one wire is way off the 127 reading, they've used a >>> wild leg, which only needs 2 transformers on the service pole. >>> >>> If you get that 127, then just hook the PC to that and the neutral. >>> Any one of the hot wires will do. >>> >>> If you get an obviously higher reading on one wire, like above 140 >>> volts, don't hook the PC power to that one, but I would also rattle >>> the power companies cage asking for a true 3 phase circuit. >>> >>> Cheers, Gene Heskett >> I worked with another company who installed a machine in the sticks of >> Alabama just two years ago and they had 3 phase power supplied to a >> plant that way. >> The installer was outside studying the transformer setup on the pole >> when he called me and said there were only two transformers and was >> asking how could that ever work. He muttered something about the >> plant saying that they had a "wild leg" and I had to look it up on the >> internet. I had never heard of it before then. But it is still >> around. The machine had a 30 hp motor on it running a hydraulic power >> unit and it was shipped wired for 480 3 phase, so the installer had to >> make a few changes to the machine also. The rural electric power >> company people came out to explain how it would work to the installer. >> The installer was afraid to start up the machine since he was afraid >> everything would burn up with the "wild leg". :-) The term "wild >> leg" doesn't exactly inspire confidence. >> >> Years later and it is still running. > Till it fails. The grounds on ANYTHING a human can touch ought to be > verified in good condition daily. A tower climber named Walter Dooer > that I used a couple times up in Iron Mountain had a day job at a > foundry over in Kingsford, helped us pull the 8 bay ch8 antenna down so > I could replace some worn thru & leaking feed lines, got it down & went > back to work at the foundry the next morning, and something in the > pendent that ran an overhead hoist, all of which ran on 480 volts, > apparently shorted to that third leg, which was over 600 volts and when > Walter grabbed it to run the hoist, it punched thru his shoes, or he was > leaning against the steel guard rails of the walkway, whatever. That was > the last thing Walter ever grabbed, I went to the services 2 days later > in Crystal Falls. Walter was a good man, but left a wife already > suffering from dementia. > > I didn't trust it then, and I damned sure don't trust it now after it > cost me a good friend. That 480 volt circuits wild leg, by the formula > given by the wiki, is 832 volts. Scaled up to todays voltage standards > where the 120 is replaced by 127, the phase to phase voltage is now 508. > And the wild leg, if I punched all the buttons right, is 880 volts. > Theres not many survivors who have ever been in contact with that high a > voltage. > >> https://en.wikipedia.org/wiki/High-leg_delta >> >> Dave >> >> >> >> ---------------------------------------------------------------------- >> -------- _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > > Cheers, Gene Heskett
Its not that high, voltage wise. Or at least it should not be... Still, plenty hot enough to kill someone. http://www.ccontrolsys.com/w/Four_Wire_Delta_Circuits I've bumped into 277 volts (480 to ground) only once 20+ years ago on the back of my hand and I can tell you exactly what machine was, where I was standing and where I ended up after I was propelled backwards. It took me a while to recover my vision as I blacked out and I was very sore for the rest of the day. Fortunately I was not well grounded. That was back when 480 motor contactors had all of their terminals exposed right on the front of the contactors - like the AB 509 series. They don't make those anymore and for good reason. http://www.relectric.com/Store/Motor-Control/509-EOA/FSSS/New?mm_campaign=39f53512d73359a9ed1fb13bb4230c66&keyword=&utm_source=Google&utm_medium=CPC&utm_campaign=Google-Shopping&gclid=CNTr-rXj0ckCFYOEaQodPv4E2w Prior to that I was shocked several times by vacuum tube circuits that ran close to 1000 volts but that didn't compare to my one experience with 277 to ground. I still work a lot with 480 VAC (this week in fact) but I am more careful now and the components are better and it is harder to make contact with the circuitry due to all of the "finger safe" features built into modern power components. Dave ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
