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Best Grounding Electrode Conductor method listed in 690.47(C)

Best Grounding Electrode Conductor method listed in 690.47(C)

Best Grounding Electrode Conductor method listed in 690.47(C)

I'm trying to determine which of the (3) grounding electrode conductor methods listed in 690.47(C) would be the best for my application.

I have a new small structure which will have both a new AC main panel as well as 3 inverters connected on the load side of this panel. Per 690.47 I need a grounding electrode for the DC side of the inverters, and per 250.32 I need an grounding electrode for the new AC panel bonded to the ground bus in the panel. In looking at 690.47 I see there are (3) options for installing both the DC and AC grounding electrode conductors.

For this instance the inverters are located directly next to the AC panel. Therefore I find that installing two seperate AC and DC electrodes and bonding them as listed in option 1 (690.47(C)(1)) would require driving two ground rods in close proximity (seperated by 6ft as required)

The second option (690.47(C)(2)) would allow me to install one ground rod at the location of the equipment but would then require me to tap the electrode itself or tap the main grounding electode conductor to supply the three inverters.

The third option (690.47(C)(3)) would allow me to install one grounding electrode and connect it to the ground bus of the AC panel. From there I can then run a combined GEC/EGC to the inverters by connecting directly to the ground bus in the AC panel. This would also allow me to not have to run an EGC to each inverter. This seems like it would be the easiest of the 3 options. My question is if I run a combined GEC/ECG from the ground bus in the AC panel can I then tap this conductor as listed in 250.64(C) in order to connect to all 3 inverters?

Although option 3 seems like the best option in this case I'm curious if there is a reason for choosing one of these options over the other or if one is a better practice? Do you guys agree that option 3 is my best be in this case?

RE: Best Grounding Electrode Conductor method listed in 690.47(C)

Option 2 is often the easiest. You don't need to install a grounding electrode, but run the DC grounding electrode conductor to the existing AC grounding electrode.  Option 3 is also good, but the combined DC grounding electrode conductor/AC equipment grounding conductor needs to be continuous all the way through.  Most electricians will cut it to land it in any disconnects or splice boxes it goes through and then it no longer meets the requiements of a GEC.

RE: Best Grounding Electrode Conductor method listed in 690.47(C)

Thanks jfpe!

I am installing a new AC panel right near the inverter so I'll be installing a new grounding electrode anyway.  So if I install a new grounding electrode am I able to run 1 grounding electrode conductor from the grounding electrode and then tap of the grounding electrode conductor using one of the methods listed in 250.64?  I know you said that the GEC must be continuous and cannot be spiced however can it be tapped to supply the (3) different inverers using one of the approved/listed method?

Even if option 2 is used do I have to run 3 different DC grounding electrode conductors from the 3 inverters to the AC grounding electrode or can I somehow tap these as well?

I also just realized that the (3) inverters in question are transformerless inverters.  Although I'm not completely familiar with the design of these inverters I do know there is no transformer between DC and AC sections of inverter and that the DC side is ungrounded.  Does the transformerless inverter and the ungrounded DC system change anything in regard to the grounding electrode conductors installation in 690.47(C)?  Should the AC and DC gounding systems be bonded together?

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