GEC size under 690.47(C)(1)

[shortcircuit2]

A solar system is installed on the roof of a building with a existing 200amp utility service with a #4 copper to the metal water pipe. (note that the largest DC system conductor will be a #2 copper conductor to a combiner box)

When using method 690.47(C)(1) for a GEC system for the utility interactive inverter grounding system, and I install ground rods as my new electrode...250.166(C) allows a #6 awg copper to the ground rods from the inverter.

Then 690.47(C)(1) says to bond the DC grounding electrode to the the existing buildings AC grounding electrode with the LARGER size of the existing AC GEC (#4cu) or the DC GEC (#6) as specified in 250.166

So you would have a #6 copper to the ground rods and a #4 as the bonding jumper? Is my interpretation right?

 

[jaggedben]

I don't find anything wrong with your interpretation.

Note that if you use one of the other methods in 690.47, the #4 is not required. (Adding DC grounding electrodes is optional under 2011. But you probably knew that.)

(I'm a little surprised that a rooftop system with a #2 DC conductor is being installed on a 200A service. Are you doing a line side tap?)

 

[shortcircuit2]

Thanks for the feedback Ben!

We have a 3phase 208 4wire existing service with 3-15KW no neutral needed inverters being installed. The 1-gang meter will be changed to a 2-gang for the solar connection...so similar to line side tap.

So I was reviewing grounding electrode system options under 690.47 and under (1) you can install a #6 to the rods....but then need a #4 bonding jumper to the metal water pipe. This seems to contradict proper sizing as instructed under 250.64(F)...

You wouldn't run a #6 to a ground rod and then jump to the water pipe with a #4 in service work?

 

[jaggedben]

You wouldn't run a #6 to a ground rod and then jump to the water pipe with a #4 in service work?

I agree it does not seem to make much sense. But I also agree with your interpretation of what the wording of the code requires.

 

[shortcircuit2]

I agree it does not seem to make much sense. But I also agree with your interpretation of what the wording of the code requires.

Yes we start with #2 DC system conductors...drop 2 rods and I can get away with a #6 GEC...and upsize to #4 bond to the metal water pipe. Doesn't seem to meet the intent for proper GEC sizing for the metal water pipe electrode. Loophole that needs work I guess.

By using 690.47(1)...the existing GES does't have to meet the requirements of article 250 part III

 

[jaggedben]

By using 690.47(1)...the existing GES does't have to meet the requirements of article 250 part III

Not sure I agree with that. Maybe you meant that the new DC GES doesn't have to meet those requirements. But then, logically it should only have to meet 250 Part VII, not part III. (There I go applying logic to the NEC. :lol

It does seem that the 690.47(C)(1) could be read to require a ridiculous-sized bonding jumper. It seems that this section should reference the requirements of 250.66 rather than the existing AC GEC. In other words, if I'm connecting rods to my AC GES, the requirement shouldn't be larger just because there's a PV system involved. At least that's the way it seems to me.

To be honest, I've never seen the 690.47(C)(1) method used except for groundmounts and separate buildings.

 

[shortcircuit2]

Not sure I agree with that. Maybe you meant that the new DC GES doesn't have to meet those requirements. But then, logically it should only have to meet 250 Part VII, not part III. (There I go applying logic to the NEC. :lol

It does seem that the 690.47(C)(1) could be read to require a ridiculous-sized bonding jumper. It seems that this section should reference the requirements of 250.66 rather than the existing AC GEC. In other words, if I'm connecting rods to my AC GES, the requirement shouldn't be larger just because there's a PV system involved. At least that's the way it seems to me.

To be honest, I've never seen the 690.47(C)(1) method used except for groundmounts and separate buildings.

The second paragraph of 690.47(C) says when using the methods of C(2) or C(3), the existing ac GES shall meet the requirements of article 250,Part III