Jeff, I understand and appreciate the nuances of your question. I guess what I am trying to convey, perhaps unsuccessfully, is that it is unwise to attempt to make a case for an exception to the NEC based upon "conventional wisdom." I have attended many IEEE seminars on grounding and bonding where similar arguments were advanced. Because of the liabilities that arise when modifications to hospital grounding systems occur, the conservative approach is always the best. My advice is to always ask the AHJ (Authority Having Jurisdiction) to provide an interpretation in writing. His or her interpretation of the NEC will always trump that of a hospital electrician, or even a consulting engineer. The answer to your specific question varies, depending upon the opinion of the AHJ, and nothing I or you say or think will change that,
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo Sent: Friday, July 18, 2008 7:39 PM To: [email protected] Subject: RE: [Repeater-Builder] Switching a Repeater Betwen AC Sources > Jeff, > > Whether multiple ground paths exist is irrelevant. What the > NEC requires is > a direct, low-impedance fault return path for each branch circuit, > considered individually. You cannot dispense with any ground > paths because > you think there exists alternate paths. While it is true that parallel > paths may decrease the total impedance to a fault on any one > branch circuit, > that in no way constitutes license to eliminate a required grounding > connection. > > 73, Eric Lemmon WB6FLY I KNOW! I'm not trying to eliminate the required EGC run along with the current-carrying conductors. What I'm asking is why you originally said that you should switch the EGC supplied by the two outlets rather than tying the two together. I had asked if there were any provisions in NEC that allowed for EGC's (whether from two different SDS's or otherwise) to ever be switched, as I can't recall there being any such case allowed in NEC. You replied that by tying EGC's together that you would create a new path whereby new, harful currents could flow. I replied that there always exist multiple EGC paths, whether desired or not, and in the instant case, there are, or would be, paths between the EGC's of the two systems whether or not you tied them together. So, my question remains, is there a case to be made where it is desirable, or even allowable, that the EGC can or should be switched? Let's assume that in the instant case (the hospital) that they are SDS's. --- Jeff WN3A
