We are adding essential circuits and panelboards to a facility that previously had none. We are installing the essential circuit panelboards in a different part of the building than the normal (existing) branch circuit panels are located. The normal branch circuit panels supply lighting and receptacles in the same rooms that our newly installed essential circuits are in. I do not see any exceptions to 517.14, and unless I am missing something it looks like we will be required to comply. I was trying to find a workaround as it is not going to be easy to get a bonding conductor to those remote panels.
The requirement appears to add nothing to the (general) requirement to run a ground wire / EGC with all feeders- and your grounds are required to be connected at transfer switches, transformers, etc. as well.
I could see this requirement as making sense if you had planned on using the conduit as your ground. As I see it, though, you're going to be running an EGC a lot larger than #10 anyway.
As I understand the trade, every panel has a nice, big, fat ground wire going from the ground buss of the source panel to the ground buss of the fed panel. Even where you have different systems interconnect - for example where there is a transfer switch - you have those EGC's.
All that remains is the mater of size- and I'm pretty hard pressed to imagine a circumstance where this feeder EGC could ever be sized as small as #10.
Is 517 asking you to run an additional EGC? Or, does this requirement address the idea that some might use the conduit of the feeder as the EGC between panels? (If so, then wouldn't the rest of the NEC have 'caught up' to 517 and made this clause redundant?)
Or, perhaps, is this requirement addressing the use of multiple ground busses in the same panel? Personally, I've never been comfortable with relying on the mounting screws and panel case as the only means of connection. If so, then the #10 wire would be 'upsizing' if all the circuits landing there were 15 or 20-amp circuits.
That last condition can't be the OP's issue, as he's asking about panels well separated from each other.
Let me stretch my imagination a little bit further ... what about different systems? Say, the 120v convenience circuita and the 480v mega-machine? Hmm. Those could be from separate services .... bonds back to the service, service bonded to grounding electrodes ... different grounding electrodes are to be connected .... yup, there's the bond, already present. ----------------
Have I been in error in believing that you cannot rely on the conduit as yout EGC for feeders? Is that where I'm getting confused? Are folks out there still feeding sub-panels without pulling an amp-sized green wire in the pipe?
517.14 Panelboard Bonding. The equipment grounding terminal buses of the normal and essential branch-circuit panelboards serving the same individual patient care vicinity shall be connected together with an insulated continuous copper conductor not smaller than 10 AWG. Where two or more panelboards serving the same individual patient care vicinity are served from separate transfer switches on the emergency system, the equipment grounding terminal buses of those panelboards shall be connected together with an insulated continuous copper conductor not smaller than 10 AWG. This conductor shall be permitted to be broken in order to terminate on the equipment grounding terminal bus in each panelboard.
Section 517.14 requires that where two or more panelboards supply the same patient vicinity and are supplied from different emergency transfer switches, the equipment grounding terminal bars must be bonded together with an insulated conductor not smaller than 10 AWG.
This is in addition to the EGC going back to the distribution equipment and is just to mitigate any ground shift along the way by bonding all panels in the patient care area together. It is similar to the bonding we do in a pool.
Well RenoŚ I don't profess to being an expert on hospital wiring or anywhere near what some people are who actually install the systems. I do know that the code panels have wrestled with the bonding/grounding wording for some time and will continue. The 2011 code eliminated the term "grounding conductor" as an example of the confusion. I do believe the goal in 517 is to "Bond" the grounding bus' together to eliminate any difference between them. The analogy that Greg offered is valid and I will have to agree that it seems overkill for the requirement in 517 to have to run a seemingly redundant #10 wire between grounding bus' but that's what it says.
The above is correct. ALL panels serving the patient care area MUST have the ground termination bars bonded with a min. #10 insulated, continuous copper. This is in addition to the ground conductor with the feeders.
Reasoning is that there is the availability of multiple power sources in patient care areas and the bond assures a zero potential. Greg hit it right on.
To those not familiar with HC facilities, it may seem like overkill; not being aware & getting a 'red tag' may seem crazy, but...it is what it is.