On 11/11/2011 7:11 AM, Brian May wrote: > What is meant by "bonded to the ground"? Does that mean connecting the > nuetral leg of the transformer to the ground? If so, why use the transformer > at all when i can just go from a leg to ground? >
If the 3 phase service is fed from a delta connected transformer there may not be a neutral... That was very common in older plants. Now most newer plants use delta-wye transformers so there is a neutral connection at the center of the wye and that point is "bonded" or connected to ground at the tranformer. At that point a real ground is also established via ground rods. You asked how do more 3 phase machines derive 120 VAC from a 3 phase input, so I was trying to answer that question. If you look at the bus duct systems used in most plants in the US, most of them only have 3 bus bars - no neutral is available. A protective/safety ground wire is assumed. Protective ground connections are always made to machines. Generally the first stop for a protective ground in a power or control cabinet is ground bus bar mounted in the corner of the steel cabinet. And the steel cabinet is normally connected to the machine frame. The protective/safety ground is never used to transmit power. Using it for a power return path is a huge no-no. If you need a neutral, you need to run another wire otherwise you are defeating the purpose of the protective/safety ground. >>>why use the transformer at all when i can just go from a leg to ground? If you think about that statement for a moment; you will realize that you just suggested that you connect the power "hot" line to the frame of the machine via the load. A very bad idea. Dave ------------------------------------------------------------------------------ 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
