I was in a plant and the maintenance guy was bitching about blowing up a plc he just hooked up and I asked him where he hooked it up... he showed me where the breaker was and it was on the 277 lighting circuit of a 3 phase panel.
On 12/27/2015 9:25 PM, Dave Cole wrote: > Well, if you ran a neutral to the BP what would you use it for ?? :-) > > It isn't required by the NEC. > > What you can't do is to tie a 120 VAC load between a hot wire and the > protective ground (which JT is not doing ). > > I do a lot of machine wiring and I was redoing a machine for a major > electrical manufacturer in the US (although this particular plant does > hydraulics) > and the plant maintenance nitwits tied a relay coil between a 480 volt > hot leg and the protective ground because they did not have a neutral in > the control cabinet and they had a 277 volt relay! 8-O > > I ripped out the added "circuitry" and wrote a note to the maintenance > mgr and explained that if the protective ground wire had became > disconnected from the power feed that the machine frame would become hot > to ground through the 277 volt relay coil! > > Dave > > > On 12/27/2015 6:21 PM, John Thornton wrote: >> The VFD filter has no place to connect a neutral... only hots and ground. >> >> On 12/27/2015 5:10 PM, Gene Heskett wrote: >>> On Sunday 27 December 2015 17:07:15 John Thornton wrote: >>> >>>> I've built a bunch of automation machines for Briggs and Stratton and >>>> they never pull a neutral only 3 240v hots and a ground. We always >>>> have a control transformer for the 120v stuff... I have the same here >>>> now. >>> After an hours searching thru it, and its the 1996 issue, a 240 volt >>> single phase line w/o a neutral is legal if it goes only to that machine >>> AND the machine was designed for that power configuration, eg is >>> designed to run on 240 for everything. >>> >>> IOW if it goes anyplace else in the building besides that machine, it has >>> to have a neutral too. And of coarse grounded is a given. >>> >>> So in your case, you can utilize a 240-120 stepdown that is NOT an >>> autoformer. And from whats been said, that is what you are doing. >>> >>> However, speaking as a C.E.T., not having the neutral so that the filters >>> you are installing can ship their noise back up that separate circuit, >>> effectively isolated from what is supposed to be a nice quiet ground, >>> does seem like it would put a lot of the absorbed noises into the >>> grounding system. And unless putting the filters in fixes it, making me >>> just a worry wart, I believe this may be much of your noise problem. >>> >>> Since we've come 19 years into the future since my copy of the NEC was >>> put to bed & sold, with more efficient (and more noise sensitive) ways >>> to do things now, I'd expect that a current copy of the NEC would more >>> than likely have some additions designed to head off problems like this. >>> >>> Unfortunately a current copy is now at or somewhat north of a 120 dollar >>> bill. >>> >>>> On 12/27/2015 3:52 PM, Gene Heskett wrote: >>>>> On Sunday 27 December 2015 16:17:20 John Thornton wrote: >>>>>> well there is no neutral because it's a 240vac circuit only... >>>>> The only reason there is not a neutral is that the wire was never >>>>> pulled. And I am not sure that missing neutral is NEC kosher. My >>>>> copy is now 17 years old, so I think I'd check a newer one to be >>>>> sure. With it, you wouldn't need the stepdown and isolation tranny >>>>> because you would then have a pair of 120 circuits available in the >>>>> machine. But those loads MUST return on the neutral, they cannot >>>>> use the static ground. >>>>> >>>>>> On 12/27/2015 12:16 PM, Bruce Layne wrote: >>>>>>> On 12/26/2015 06:51 PM, John Thornton wrote: >>>>>>>> There is no neutral in the machine, only L1 L2 and GND. The >>>>>>>> Neutral for the house is bonded to ground at the panels. >>>>>>> Electrician's Joke: >>>>>>> >>>>>>> Q: What's the difference between neutral and ground? >>>>>>> A: About six inches. >>>>>>> >>>>>>> There's a very good reason the return current is carried on the >>>>>>> neutral and the ground should not carry any current in normal >>>>>>> circumstances, but we do need to understand that electrons don't >>>>>>> care about our conventions. They're just as happy returning via >>>>>>> the ground wire. They don't know that the green wire is off >>>>>>> limits for all but emergency traffic. >>>>>>> >>>>>>> The concept of ground/neutral functional equivalence is also a >>>>>>> real life saver for anyone who might otherwise consider standing >>>>>>> barefoot on a basement floor while hot wiring any line powered AC >>>>>>> circuit. >>>>> Cheers, Gene Heskett >>>> ---------------------------------------------------------------------- >>>> -------- _______________________________________________ >>>> Emc-users mailing list >>>> Emc-users@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/emc-users >>> Cheers, Gene Heskett >> ------------------------------------------------------------------------------ >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
