transformer inverter vs. transformerless inverter - worth the savings?

[Jest Waitn]

That is not going to happen, so forget about it. It is required by code, and it would be extremely dangerous if you did not. additionally it can wreak havoc on your electrical system. To the point your TV and electronics would not work. So just get that idea out of your head as it is Best Practice.

i'm not refuting what you say or arguing with you, but in the below article on pv system ground faults, how does the last paragraph on the page relate to what you say? it seems that the author is saying the pv ground should NOT be carried into the inverter. this is for a grounded pv system (i assume the author is referring to using a transformer inverter).

http://solarprofessional.com/articles/operations-maintenance/pv-system-ground-faults/page/0/2#.WSXmMHUrJpR

[sensij]

i'm not refuting what you say or arguing with you, but in the below article on pv system ground faults, how does the last paragraph on the page relate to what you say? it seems that the author is saying the pv ground should NOT be carried into the inverter. this is for a grounded pv system (i assume the author is referring to using a transformer inverter).

This quote? It explains why you can't ground a system conductor anywhere *except* inside the inverter.

Ground faults can also be introduced by wiring errors. If the grounded dc current-carrying conductor in a grid-direct PV system is connected to ground outside the inverter - at the dc service disconnect, for example - this will activate the GFDI protection system, and the inverter will shut down indicating a ground fault. Similarly, some off-the-shelf dc monitoring equipment has one of the current-carrying conductors connected to ground. If this equipment is installed in a PV monitoring system, the GFPD will see it as a ground fault. When some transient voltage surge suppressors and lightning arrestors are wired in series with one of the dc conductors, the GFPD may recognize these as ground faults as well.

[Sunking]

i'm not refuting what you say or arguing with you, but in the below article on pv system ground faults, how does the last paragraph on the page relate to what you say? it seems that the author is saying the pv ground should NOT be carried into the inverter. this is for a grounded pv system (i assume the author is referring to using a transformer inverter).

http://solarprofessional.com/article...2#.WSXmMHUrJpR

No problem I did not take it that you are arguing or debating. The problem you are having is not understanding what the author is trying to tell you. You came away with the impression the AC and DC system grounds must be isolated and separate from each other. That is not what the author is saying. If that is what he is implying, then he should be shot as a pretender and fraud, because that can fry your equipment and get you killed.

I don't want to dive into the technical part because it is out of the scope of this forum, and frankly quite a long and boring lecture not all professionals ever get their heads wrapped around. The short of it, pun intended, all grounds in a facility MUST BE COMMON and made irreversible and fool proof by code. Both your AC and DC systems meet at some point and frequently occupy the same space. Thi smeans the is a very high chance one system can make accidental or intentional contact with each other. If the two systems are not bonded intentionally together and made common, an extreme potential of difference will exist. In order for the fuses, breaker, and GFD to operate properly must have a path to return a Shorted Fault back to the source. Example if the Utility AC power comes into contact with the DC system, and no common Fault Path is provided, the fuses, breakers, and GFD would not operate leaving hot AC power on all the surfaces for you to touch and come into contact with.

ZAP, you just electrocuted. Had you had the required bond, fault current would have flown back to the utility source and operated the breaker clearing the fault. It would also take down the DC side telling you have a problem to fix, rather than discovering by being electrocuted and equipment damage on top of it.

The AHJ knows this and if he caught it would fail your inspection. Thus why I said not going to happen for your own protection and safety. i am a pro and covering your butt just like the AHJ. Call us SOB's but we have your best interest at hand. That is what we get paid to do, and liable for our work. You on the other hand do not know what you need to know, and if you screw up is all on you. No one to sue if you get hurt, or no one for your survivors to sue if you get killed.

[Jest Waitn]

That is not going to happen, so forget about it. It is required by code, and it would be extremely dangerous if you did not. additionally it can wreak havoc on your electrical system. To the point your TV and electronics would not work. So just get that idea out of your head as it is Best Practice.

how does this differ from what i said?

https://www.homepower.com/articles/solar-electricity/design-installation/code-corner-earth-shifting-change-grounding

[sensij]

This is what you said:

before buying a transformer inverter, i would want to make certain the AHJ will approve separate grounding (a/c and d/c separate).

This is what the article says:

Now, the only type of PV system permitted to be solidly grounded has only one or two PV source circuits, and no DC circuits on or in a building. This limits these applications to small, load-focused, PV-direct systems and perhaps some smaller battery-based systems.

In grid tie systems, you don't ground the DC conductor directly, separately from the AC ground. The DC ground is provided through the inverter, shared with the AC ground, and in 2017 NEC language, is considered "functionally grounded", not "solidly grounded" because there is a fuse in the circuit.

There is more flexibility in how you handle the equipment ground, but that is true regardless of whether you use a transformer based or transformerless inverter.

[bcroe]

This is what you said:



This is what the article says:



In grid tie systems, you don't ground the DC conductor directly, separately from the AC ground. The DC ground is provided through the inverter, shared with the AC ground, and in 2017 NEC language, is considered "functionally grounded", not "solidly grounded" because there is a fuse in the circuit.

There is more flexibility in how you handle the equipment ground, but that is true regardless of whether you use a transformer based or transformerless inverter.

Lets not confuse the grounding of the PV framework (solid), with the PV DC conductors, which in my system
ground negative through a small fuse in the inverter, in turn monitored by a GFI circuit. Bruce Roe

[sensij]

Lets not confuse the grounding of the PV framework (solid), with the PV DC conductors, which in my system
ground negative through a small fuse in the inverter, in turn monitored by a GFI circuit. Bruce Roe

Yeah, I hesitated to bring it up, but I don't understand why the OP seems to be struggling. Equipment ground (framework ground) is a completely separate topic tfrom the system ground differences between different types of inverters, but could be why he is thinking another ground is required.

It is sort of interesting that NEC has finally gotten around to accurately defining your DC system as "functionally grounded", distinct from "solidly grounded" systems that have a true bond to ground. In this new definition, your ground fuse connected DC conductor is no longer allowed to be white... in any previous code version, white (or gray) was required. By commonizing the wire requirements between transformer based and transformerless inverters, that is one less hurdle to switching between them.

[Jest Waitn]

This is what you said:



This is what the article says:



In grid tie systems, you don't ground the DC conductor directly, separately from the AC ground. The DC ground is provided through the inverter, shared with the AC ground, and in 2017 NEC language, is considered "functionally grounded", not "solidly grounded" because there is a fuse in the circuit.

There is more flexibility in how you handle the equipment ground, but that is true regardless of whether you use a transformer based or transformerless inverter.

i have never used or wired a transformer inverter. it seemed from the language i read that the d/c ground was a 'direct ground' from either the +/- side of the pv array to the ground rod.

[Sunking]

i have never used or wired a transformer inverter. it seemed from the language i read that the d/c ground was a 'direct ground' from either the +/- side of the pv array to the ground rod.

That is where you went wrong and got thrown off track. Sinsij explained it fairly well. Kudos and Warm Fuzzies.

[Jest Waitn]

here is a good article on grounding i just found, and yet he is grounding the -dc?

http://africanenergy.com/new/wp-cont...outh-forty.pdf

[sensij]

here is a good article on grounding i just found, and yet he is grounding the -dc?

http://africanenergy.com/new/wp-cont...outh-forty.pdf

That article is more than 17 years old. I'm not sure when 690.42 was added to the code, ground requirements have changed a lot over the years, but it contains none of the exceptions suggested in your link.

Here is the 2014 NEC language, emphasis mine. I'm not sure how it could be any clearer.

690.42 Point of' System Grounding Connection.
The dc circuit grounding connection shall be made at any single point on the PV output circuit.

Informational Note: Locating the grounding connection point as close as practicable to the PV source better protects the system from voltage surges due to lightning.

Exception: Systems with a 690.5 ground-fault protection device shall be permitted to have the required grounded conductor-to-ground bond made by the ground fault protection device. This bond, where internal to the ground fault equipment shall not be duplicated with an external connection.

The inverter counts as a 690.5 device. Per the exception shown below, if you found an inverter without integral ground fault protection, you could do the DC grounding at the array. As you've already said, though, the inverter you are considering includes ground fault protection, as do all currently available grid-tie inverters that I'm aware of.

690.5 Ground-Fault Protection. Grounded dc PV arrays
shall be provided with dc ground-fault protection meeting
the requirements of 690.5(A) through (C) to reduce fire
hazards. Ungrounded dc PV arrays shall comply with
690.35.

Exception: Ground-mounted or po!e-mounted PV arrays
with not more than two paralleled source circuits and with
all the source and the output circuits isolated from buildings
shall be permitted vvithout ground fault protection.

[Sunking]

here is a good article on grounding i just found, and yet he is grounding the -dc?

http://africanenergy.com/new/wp-cont...outh-forty.pdf

I know John Wiles quite well. We both sat on NEC Code Making Panels.

Anyway that article has nothing to do with your application. and as John discovered, dangerous. That article is written for Off Grid Battery Systems which means no commercial AC service on the property. John bless his heart is a Phd and Instructor, he has no real world experience. A lot of what John writes has been blasted out of NEC like 690.47.D in this nice 26 minute video by Mike Holt. You will see my smiling face in the video as I am one of his moderators and he will discuss just how dangerous John can be. Mike has never made such a strong statement ever, and is supported by all AHJ's and engineers as most have amended out John's requirements he snuck through the 2014 cycle. This is what happens when you have advocates get involved in real world applications.

Anyway that article has nothing to do with your Grid Tied application.

Here is the video. Listen to Mikes opening statements and OPINION.

[bcroe]

It is sort of interesting that NEC has finally gotten around to accurately defining your DC system as "functionally grounded", distinct from "solidly grounded" systems that have a true bond to ground. In this new definition, your ground fuse connected DC conductor is no longer allowed to be white... in any previous code version, white (or gray) was required.

Hmm, between combiner and inverters my installer put in 2 pairs of 6 ga for DC, black for + and white for -. Ground
is 8 ga white, wonder how far off the colors are? From the inverters on, grounds are green. All the panel wiring is
10 ga black PV wire, with pairs numbered and polarity indicated at both ends. Bruce Roe

[Jest Waitn]

I know John Wiles quite well. We both sat on NEC Code Making Panels.

Anyway that article has nothing to do with your application. and as John discovered, dangerous. That article is written for Off Grid Battery Systems which means no commercial AC service on the property. John bless his heart is a Phd and Instructor, he has no real world experience. A lot of what John writes has been blasted out of NEC like 690.47.D in this nice 26 minute video by Mike Holt. You will see my smiling face in the video as I am one of his moderators and he will discuss just how dangerous John can be. Mike has never made such a strong statement ever, and is supported by all AHJ's and engineers as most have amended out John's requirements he snuck through the 2014 cycle. This is what happens when you have advocates get involved in real world applications.

Anyway that article has nothing to do with your Grid Tied application.

Here is the video. Listen to Mikes opening statements and OPINION.

ok. wow. let me make certain i understand what he is saying about grounding wrt to a solar array.

the main panel has a bonded ground. the ground rod used for a chassis or frame ground at the pv array, should NOT be connected back to the bonded ground. it should be terminated at the disconnect switch or connection box.

[inetdog]

What MH is saying is that if there is a local ground rod driven which is physically (and therefore electrically in terms of induced voltage in local earth from enormous lightning currents) distant from the main ground electrode grid it must be connected via a GEC (wire or structural steel or other excellent conductor) back to the primary GES of the building. Just connecting the panel frames, racking, and array end electrical wiring enclosures to an isolated local electrode, with only an EGC to bond them back to the main building bond grid, will cause high currents to flow in that EGC with equally high offset voltages that can destroy electronics and/or start fires.
It is easier to simply avoid the local earth electrode in the first place.

And if I have misstated anything above, I am sure Sunking will correct me.