On Thursday 10 December 2015 12:49:17 Todd Zuercher wrote: > I know you could pull single phase from the 3phase, but it is > essentially that already, just coming from the panel on the wall > instead of splitting at the machine. This machine is fed by 3 beakers > on the panel. (I just checked) I was wrong before the 2 spindles are > on one 208 3phase beaker, the 4 servo drives are on one 208 single > phase, and the PC and other low voltage stuff is a 110 beaker. All 3 > right in a row in the same panel box. I guess there is the potential > of a ground loop problem from these 3 separate feeds (that each have > their own ground wire.) What would be the right way to remedy this?
Common at the neutrals should not be a problem, but any connection from that neutral to the static ground & ground rods, other than the one usually in the meter head, is a no-no. Basically, no neutral current should ever flow on the static ground system. If you can get an amprobe clamp around that static wire where it heads for the meter, and you see any current, something is miss-wired. Break into each static by removing it from the insulated bus strip, put a short wire to extend it back to the strip, and measure each with the amprobe. When you see a reading, start opening duplexes etc and find where its crossed. Just in case the leakage is serious, handle that bare wire with insulated tool handles. Any slight sparking when the wire is becoming disconnected would also be a good indicator. Some might be the end equipments entrance noise filters but those will normally be well under .010 amps, unless they have failed. And yes, I have seen them blown. :( The available volts in that case where they haven't failed but have lots of both sides to static bypassing should be slightly less than 1/2 the line voltage. > ----- Original Message ----- > From: "Gene Heskett" <[email protected]> > To: [email protected] > Sent: Thursday, December 10, 2015 4:06:07 AM > Subject: Re: [Emc-users] linuxcnc 2.7.3 - mesa 7i77 update > > 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 Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Some mill pix are at: Genes Web page <http://geneslinuxbox.net:6309/gene/GO704-pix> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
