Transformer Grounding

[Lee Graves]

Should you run an equipment grounding conductor with your phase conductors feeding the line side of a stepdown transformer? Inside the transformer, once you bond the grounded conductor to the grounding conductor and to the building steel, wouldn't you have parallel paths back to ground with a difference in potential? (1 path via the building steel and 1 path via the line side equipment grounding conductor) Is that a bad? Now throw an extra piece of rebar (Ufer ground) into the equation, and you could have (3) different paths back to ground with (3) different potentials? If you do run an equipment grounding conductor on the line side, and inside the transformer you bond your grounded with your grounding, is it necessary to bond to the building steel or to anything else? Please help!


Lee Graves

 

[iwire]

Lee, run the EGC with the primaries and tie it in.

Regardless of running a copper EGC with the primaries or using the conduit system as the EGC the transformers enclosure must be connected to the EGC of the supplying electrical system just like any appliance.

On the secondary side you must tie XO to the enclosure, into building steel if it exists and you may also have to bond to a local metal water system.

There will be very little current flowing on any of this under normal conditions. During a ground fault all these paths will only serve to open the overcurrent device quicker.