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HeatSpring PV Course Blog

690.47(C)(3) Combination dc Grounding Electrode Conductor/ac Equipment Grounding Conductor


Q:

Hi Sean: On the PV Electrical System Design Lecture I got a little confused by the discussion on inverters and grounding. If power leaves the inverter, how are you "combining" the DC GEC? The slide says DC GEC may be combined with AC EGC, but I couldn't follow why this works
Also, when you say the right size being a number 8, I take it you mean the AC EGC should be 8 awg?
Thanks!

A:

It used to be that we would be required by the building departments to have a separate grounding electrode conductor (GEC) often going to a separate ground rod (electrode) for our solar inverters.

Now most AHJs are letting us use the pathway to ground of the ac equipment grounding conductor (EGC) as a dc GEC as it says we can in 690.47(C)(3).

This means that the ac EGC also works as a dc GEC at the same time.

If we are using the combo ac EGC/dc GEC method, we will have to make sure the conductor is large enough using table NEC 250.122 for the ac EGC and NEC 250.166 for determining the size of the dc GEC. After finding out which conductor is required to be largest, we will use the largest required conductor of the two. For residential PV, 8AWG is always the larger.

In the NEC, it is not 100% clear to the experts if we have to size it as a 8AWG conductor for ungrounded PV systems and many inverter manufacturers are not recommending 8AWG. There is no perfect answer here for the 2014 NEC and some arguments out there.

These questions are covered in the HeatSpring Advanced PV Class.

Thanks,

Sean White



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