GES for Transformerless Inverters

[shortcircuit2]

Do we need to install a Grounding Electrode System for Grid Tied transformerless inverters?

 

[jaggedben]

Do we need to install a Grounding Electrode System for Grid Tied transformerless inverters?

Your question implies that there is a utility service, which should already have a GES. The code has allowed the premises GES to provide both AC and DC grounding since at least the 2008 cycle. You should not have to install a new GES or do any work on any GES unless the AHJ requires you to bring an older premises GES up to current code (e.g. install a rod where there was only a water bond).

Regarding transformerless inverters, the 2014 code makes a distinction between grounded and ungrounded DC systems. A transformless inverter indicates an ungrounded system. (An transformer inverter usually, but not always, indicates a grounded system. A grounded system always has a transformer in the inverter, unless it's bipolar.)

For an ungrounded system, the 2014 code allows equipment grounding to serve as the reference for the inverter GFDI and states that the grounding conductor from the inverter to the 'associated AC equipment' can be sized to 250.122. This could be read to imply that a transformerless inverter only requires an equipment grounding conductor, or that the conductor has to be installed like a GEC (bonding bushings, continous, etc..) but can be sized smaller than a minimum 8 awg.

Previous codes make no such distinctions.

There's also 690.47(D), which has been in and out of the code, but which is for the array and not 'for the inverter.' If your AHJ requires you to follow that (see other thread started today), then it will probably make no difference what type of inverter you have.

 

[shortcircuit2]

Thanks jaggedben...I'm stuck on the new allowance in the 2014 code under 690.47(B) that allows the AC EGC to for grounding of inverters and the GFD reference.
The first part of 690.47(B) says we need a GES and then the last paragraph seems to except the GES and the EGC suffices. I'm abit confused on what the code is saying?
Or does the last paragraph just state that a GEC is not needed to connect to the GES and the EGC is all that is needed?

 

[shortcircuit2]

Here is a excerpt from a Solarpro article on my confusion...

"Ungrounded PV systems. In prior Code cycles, there was some confusion regarding grounding-electrode conductors for ungrounded systems. Section 690.47(B) now specifically allows use of an ac equipment-grounding system as the ground-fault?detection reference for ungrounded PV systems. In addition, Section 690.47(C)(3) states that a combined dc grounding-electrode conductor (GEC) and ac equipment-grounding conductor (EGC) can be installed for ungrounded systems. This combined dc GEC and ac EGC is sized in accordance with Section 250.122?as an EGC, in other words?and is not required to be larger than the largest ungrounded phase conductor. Note that this combined grounding conductor must still be unspliced or irreversibly spliced.

As an example, if a non-isolated inverter?s ac output circuit back-feeds a 30 A circuit breaker, the combined dc GEC and ac EGC between the inverter and the service panel can be sized per Table 250.122, which specifies 10 AWG copper based on the OCPD rating. Further, the combined dc GEC and ac EGC is never required to be larger than the ungrounded phase conductors of the PV system. This allows the combined grounding conductor to be sized smaller than the minimum dc GEC size of 8 AWG that Section 250.166 would otherwise require. When these sections are applied together, it is clear that non-isolated (transformerless) inverters used in ungrounded PV systems do not require a dc GEC sized per Section 250.166 to be run to a dc grounding electrode. Instead, an unspliced conductor acting as the ac EGC can be used to meet the grounding electrode system requirements for ungrounded PV systems."

This is the way you have described it to me also jaggedben...run a properly sized EGC, but I still must bond according to 250.64(E) and the EGC must be unspliced.

I understand now.

Thankyou, shortcircuit

 

[jaggedben]

As far as 690.47(B), an AC EGC system is required to be connected to a GES, but that's already the case for premises with code-compliant utility services. If you were installing an off-grid system on a building with no existing power source, 690.47(A) or (B) requires you to install a new GES.

The Solar Pro article certainly is a sensible reading of the code. But to me, the two new sentences (in 690.47(B) and 690.47(C)(3)) kind of contradict each other. If I can use an AC equipment grounding system then that implies to me that I can bond to valid EGCs such as metal raceways. And that vague phrase "associated AC equipment" is still in there, so I don't know how far this conductor has to extend.

FWIW, we have one AHJ who is allowing us to use these sections of the 2014 code even though it isn't in force in California yet. And they are letting us basically just run a normal EGC to whichever panel we are interconnecting to. (This comes along with some really heinous, non-code-based requirements for inverters with transformers). We're still throwing grounding bushings on everything just out of habit, but not making too many irreversible splices anymore. Your mileage will almost certainly vary...:lol: