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
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