Usually bigger 3 phase machines being fed with 480 volts or so will only have the 3 phases run to the machine without a neutral wire.
The reason being that Line to Neutral on a 480 volt system is 277 volts and that is not very useful for anything other than lighting. To get 120 VAC, two of the phases will be tapped (480 volts) and that will be run to a step down transformer. One the secondary side of the transformer, one leg of the transformer will be declared the hot line, and the other leg will be declared the neutral. The neutral will be bonded to the ground close to the transformer. The hot line is fused. That will establish a proper 120 VAC circuit off the 3 phase input power. You could run a separate single phase feed into the existing 3 phase power panel, but then you would have power being fed into one panel from two different sources and that gets tricky from a safety standpoint. I try and avoid doing that whenever possible. Generally when you pull the disconnect switch on a machine panel you want to kill all power in the panel for safety. A lot of machine builders are now avoiding 120 volt power system in their machines entirely. They do that by using DC power supplies that can accept high voltage input power directly. You can buy 3 phase input power supplies that will accept up to 600 VAC and produce 24 VDC. Most of the big power supply makers sell them. Dave On 11/10/2011 10:27 PM, Brian May wrote: > Ok that makes sense. > > Just out of curiosity, How do other machines do it. Our other cnc machines > only have the 3 lines and earth ground running into them... > > Sent from my iPod > > On Nov 10, 2011, at 9:01 PM, Brian Mihulka<bmihu...@hulkster.net> wrote: > > >> On 11/10/2011 08:50 PM, Brian May wrote: >> >>> This is probably an easy question for alot af the people on the list. >>> >>> I have 3 phase power going to my vfd on my machine. I want to the use that >>> same power to power all the 120 single phase components. (the dc power >>> supply for the steppers and varios other motors. ). This way i only need 1 >>> plug >>> >>> I have been reading and people say i can go from 1 leg to a nuetral or leg >>> to leg. I do not have a nuetral line so my question is will it be ok to go >>> from leg to leg for the 120 single phase? Or is there some other component >>> i need? >>> >>> Thanks >>> Brian >>> >>> Sent from my iPod >>> ------------------------------------------------------------------------------ >>> RSA(R) Conference 2012 >>> Save $700 by Nov 18 >>> Register now >>> http://p.sf.net/sfu/rsa-sfdev2dev1 >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >>> >> If its 3 phase 208, one leg to any other leg will give you 208. You >> have to have the neutral to get 120 from any leg. You should get 120 >> from any leg to ground but it wouldn't be up to code. >> >> Brian >> >> ------------------------------------------------------------------------------ >> RSA(R) Conference 2012 >> Save $700 by Nov 18 >> Register now >> http://p.sf.net/sfu/rsa-sfdev2dev1 >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > ------------------------------------------------------------------------------ > RSA(R) Conference 2012 > Save $700 by Nov 18 > Register now > http://p.sf.net/sfu/rsa-sfdev2dev1 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
