Yes, Anytime you have a 120 volt source for computer, misc power etc, you need to declare one side of the 120 vac winding the neutral (white wire) and tie that terminal to the machine frame. It similar to what is required at the service entrance of your house. The neutral is always tied to the ground at the entrance box. Oftentimes they drive a screw through the neutral buss bar in the service entrance box into the box sheetmetal and then tie a green or bare copper ground wire to the same neutral buss bar and run that to a metal water pipe or ground rod. Oftentimes they just put a green copper jumper wire between the "declared" neutral terminal on the transformer and the transformer attachment screw in the panel and they use the steel panel backplane for "ground". If you are using a single point ground just run a green ground wire from the neutral terminal on the transformer and the single point ground in the panel.
Dave On 1/1/2016 7:02 AM, John Thornton wrote: > Hi Jon, > > So tie say the 48v side to ground to create the neutral? I attached > the drawing of what I have so far on the VFD side. > > Happy New year to you and I hope you stayed dry during the recent > monsoon we got. > > JT > > On 12/31/2015 7:16 PM, Jon Elson wrote: >> On 12/31/2015 03:24 PM, John Thornton wrote: >>> I went and checked the control transformer and one side is 48v to >>> ground >>> and the other side is 79v to ground. I guess I was confused by that. >>> >> Do you have a ground connected to that winding? If not, >> then the capacitance of that winding to other windings and >> the core will set what AC potential you get at each end. >> I'm guessing you have a totally floating secondary, and this >> adds up to 127 VAC, which sounds right for a nominal 120 V >> output. You can tie one end of the winding to frame ground, >> establishing a new neutral in the cabinet for the computer, >> etc. loads. >> >> Jon >> >> ------------------------------------------------------------------------------ >> >> >> _______________________________________________ >> 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
