electricaldoc
Member
At my work we have a 480V/277V 3PH Y system with a total of about 15KA. We started out a lot smaller and pulled less than 40% of this at beginning. Now we are noticing a lot of grounding problems. Such as potential difference of 40V-50V between grounds. We are currently in a NEC class for 2005, and one of the electricians asked instructor about this. Electrician asked about our grounding grid being inadequate now that we are pulling so much more amps. The instructor agreed. This left me confused because I was under the impression that once you achieve a low impedance ground it was sufficient for any size system. I know the bonding jumpers and conductor sizes will change, but this is done as system is upgraded. I mean they will add proper sized bonding jumper every time switch gear is added, which should all add up to correct size for entire system. I feel the problem would most likely be with our bonding system that we install on equipment and circuits, and not the grounding grid its self. I know the grounding grid can derogate and get higher impedance, but this place is only seventeen years old. The code only requires 25OHMS or less to ground and this is suppose to be sufficient no matter how large of system you have. Now I realize this is only a minimum, and probably not good enough for quality power for a place our size so much lower value needed. The original grounding grid should have reached this lower level, and adding more power should not make this grounding grid inadequate. I still feel as if it is our own bonding that would be problem, and not the grounding grid. I am trying to learn most of this grounding and bonding on my own with help from soares and you guys. So please let me know your opinion, about if I am wrong or correct, and why.
Thanks
Dan
Thanks
Dan
