grounding electrode in panelboards

[vincedigital]

hi,
if i have a commercial building with 10 units, panelboards are located inside each unit, & a meter center with 600amps main disconnect & 10 meters are mounted in the building wall outside, do i still need to put grounding electrodes in each panelboards? or one by the main disconnect for the meter center will be enough?- thanks

 

[infinity]

Since there is a main service disconnect your GEC can connect there. The wiring to each panelboard will be a feeder and does not require a GEC but does require an EGC.

 

[vincedigital]

thank you for the advise.

 

[GoldDigger]

Since there is a main service disconnect your GEC can connect there. The wiring to each panelboard will be a feeder and does not require a GEC but does require an EGC.

If you were to install a ground electrode at each unit and connect it to the ground/EGC bus at the subpanel it would get a little complicated. The EGC and neutral will not be connected at that subpanel, but the local ground electrode will have to be connected back to the GES at the main disconnect.
That means that the feeder EGC must also meet all of the conditions for a GEC for that electrode.
It also gets a little complicated in how you describe that connection, since the Code does not allow an EGC to be used as a GEC but does allow a suitably sized GEC to also be used as an EGC.
The simplest resolution is simply not to create a ground electrode for each unit. If you do create one you are forced to bond it into the rest of the GES.

 

[wwhitney]

It also gets a little complicated in how you describe that connection, since the Code does not allow an EGC to be used as a GEC but does allow a suitably sized GEC to also be used as an EGC.

That seems like an unnecessarily confusing way to put the rules (as is the way 250.121(A) is written). A wire type conductor can be:

(a) an EGC if it meets the EGC rules
(b) a GEC if it meets the GEC rules
(c) both if it meets both rules.

There's nothing asymmetric about the rules.

Cheers, Wayne

 

[texie]

thank you for the advise.

While not directly related to the GEC, just be mindful of 250.104(A)(2) Buildings of Multiple Occupancy if it applies in your case.